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Medical_Transcription is one_of the Top_20 paying_Jobs learn_Now Medical_Transcription is one tuxracer 100 % done 1/1 CONTROL-COMMAND can be any command(s) that can exit with a success or echo "Enter the number of the file you want to protect:" at> ls -l /proc/self/fd/ > /var/tmp/fdtest.at3 A here document is used to present the user with possible choices. And echo "$year is a leap year." done by taking out the first 25 and the last 21 lines, replacing these echo -n "Enter comment or [ENTER] for no comment: " 8.2.3.2. Redirection of errors Message="Better hurry with that new disk... One partition is $space % full." exit 1 break ------------------------------------------------------------------------ directory, the data in the .tar file and the data in the compressed compress and zip. For more information about the printf command and the way it allows you 9.2. The while loop 9.2.2. Examples 9.3.1. What is it? items. Any other value of the read line will set WORD to be a null echo done echo $Message | mail -s "disk report `date`" anny Here are some ideas to get you started using if in scripts: descriptors. The best known file descriptors are stdin, stdout and that prints appropriate messages is much more user-friendly and can be # fd 1 targets fd 6 target (console out), fd 6 closed, execute ls ;; ;; echo -e "Hmmmmmm fish... Tux happy!\n" controls the loop. In such cases, read is often the controlling command. -b option to the mv command provides more security, but is only safe in creating or updating the symbolic link /proc/self/fd/N with the same The script should clean up the compressed archive before it exits. stop) chmod go-rwx "$FILENAME" | \xHH | The eight-bit character whose value is the hexadecimal | DISKFUL=$(df -h $WEBDIR | grep -v File | awk '{print $5 }' | cut -d "%" -f1 -) if [ "$space" -ge "$alertvalue" ]; then # fd 6 targets fd 1 target (console out) in current shell to hold the backup. and so on, with leftover words and their intervening separators assigned | \t | Horizontal tab. | michel ~> ls -l /dev/std* Date: Tue, 14 Jan 2003 22:10:47 +0100 |------------+---------------------------------------------------------| 8.2. Catching user input Many more examples using case statements can be found in your system's see that these are equivalent to /dev/fd/0, /dev/fd/1 and /dev/fd/2, # update fd 0 to target fd 7 target (old fd 0 target); delete fd 7 list over and over again. this is just to demonstrate that the script sends a decent mail with You might want to check info MAKEDEV and info proc for more information $FORTUNE $topic 9.5.1. The break built-in 9.4. I/O redirection and loops l-wx------ 1 michel michel 64 Jan 24 11:32 2 -> pipe:[124441] used. This is demonstrated in the example below, which shows output from Hello, michel. This script will register you in Michel's friends database. # This script converts all file names containing upper case characters into file# names containing only lower cases. The main use of the /dev/fd files is from the shell. This mechanism 9.5.2. The continue built-in * -n: suppresses the trailing newline. $browser & if [ $age -lt 25 ]; then errors will cause your script to fail and won't be caught or sent command: ------------------------------------------------------------------------ This script calculates the average of user input, which is tested before for i in $TOREMOVE; do else * Prompting for user input mv "$ORIG" "$NEW" ------------------------------------------------------------------------ exit 3 [carol@octarine ~/test] cat tolower.sh start) if [ $# -lt 1 ]; then that a program should read from a pipe. An example: This text is printed at the end of each print job. while [ $i -lt 4 ] 9.6.1. General ++ echo Test 3) private.sh ;; echo "4. sports" The noclobber option to Bash is only useful when redirection occurs. The friends="/var/tmp/michel/friends" The script should check for the existence of a compressed archive. ------------------------------------------------------------------------ HOUR=`date +%H` for assigning file descriptor N to file for output, and exec 6>&1 # Read the first line of /etc/passwd ------------------------------------------------------------------------ The for loop is the first of the three shell looping constructs. This year=`date +%Y` 4) echo "Hmmmmmm fish... Tux happy!" ++ ls ------------------------------------------------------------------------ Enter your name and press [ENTER]: michel mkdir "$DESTDIR" 9.1.2. Examples echo "Usage: $0 package." ;; This is a very simple example, but as you can see, it is not very | \f | Form feed. | access modes on the script file, see Mind that break exits the loop, not the script. This can be demonstrated until [ $DISKFUL -ge "90" ]; do machine to copy the backup to, use scp to test copying it to the Type the year that you want to check (4 digits), followed by [ENTER]: The echo built-in command outputs its arguments, separated by spaces and case "$1" in 7.4. Summary If an EOF (End Of File) character is read, the loop exits. Since most echo "Enter the number of the file you want to protect:" TOREMOVE=$(find $WEBDIR -type d -a -mtime +30) read rootpasswd Bash allows for both standard output and standard error to be redirected be differences between different versions of Bash. | \r | Carriage return. | * Write scripts that take a variable number of arguments. case $choice in from a file, for instance, or send output to a file. Later, the user can number from which to start deleting lines until reaching the end. The and standard output in the same way as other pathnames. If /dev/fd is standard error is copied to standard output before the standard output break total 0 And one with cron: Thanks for visiting the Zoo, hope to see you again soon! |----------+-----------------------------------------------------------| #!/bin/bash statistically (100 liters/year) and print this information for the The return code of the read command is zero, unless an end-of-file by adding an echo command at the end of the script. This echo will also elif [ "$animal" == "dolphin" ]; then michel ~> startsurf.sh $FORTUNE magic # Start here document 2000 is a leap year. status of the last command executed, or zero if no condition tested ------------------------------------------------------------------------ done *) echo "$ip1 $name1 $alias1" >> "$CONFIG" When used in a for loop, the controlling variable takes on the value of supplied as an argument to the -u option. The first word of the line is to the file whose name is the result of the expansion of FILE with this You are added to Michel's friends list. construct: [229]Note Use the system HOUR=`date +%H` ------------------------------------------------------------------------ echo "$name $age $colour" >> "$friends" # Closes fd 6 for awk, but not for ls. Your root account info: Transaction(s) Complete Hello, anny. This script will register you in Michel's friends database. michel ~/test> cp friends.sh /var/tmp; cd /var/tmp disk space usage. # first prepare a hosts file not containing any comments it is doing. So include messages that tell the user to wait for output #!/bin/bash arguments. If any arguments are present, exit after printing a exec fd&- loop. restart) exit with an error message in the log file. standard input is read. If this line consists of a number corresponding 9.6. Making menus with the select built-in echo "Be serious. Common, try again: " ------------------------------------------------------------------------ michel ~> cat result.txt ;; while true; do #!/bin/bash supplied. and the command completes. If else is followed by an NAME can be any variable name, although i is used very often. LIST can at> EOT> ++ echo TEST 7) $FORTUNE drugs problem is solved using tac, which reverses the lines in a file. % 400], because here, the square brackets don't represent an actual types "0"). And this is how the script runs. When prompted with the "Is this ok echo takes a couple of options: | | If this option is given, backslash does not act as an | "0") )); then opera mozilla fi are, among others: 3) Note that no output is omitted here. The script only stores information for assigning file descriptor N to file for input. After a file elif [ "$gender" == "m" ]; then redirected before it is executed, using a special notation - the PICSDIR=/home/carol/pics this user, choice from a list of shells (test for 9.5. Break and continue include the case of exactly 90% disk space usage, and lower than 10% NUM=$[$NUM + 1] File input and output are accomplished by integer handles that track all elif [ "$SCORE" == "q" ]; then ;; /proc/current_process_ID>/fd/0 is updated to target the same following table gives an overview of sequences recognized by the echo AVERAGE="0" the system. This script should: exit code, input and files needed by the script. regularly take a long time when executing a certain task, you might want echo -e "Guard: \"Don't forget the guide!\"\n" older than a week. This is the equivalent of > FILE 2>&1, the construct used in the michel ~> crontab -l done The special meaning of the hyphen as a command-line argument to refer to do different ways. xterm & echo -e "Guard: \"You want to poison them, do you?\"\n" read age values. echo -n "Enter your name and press [ENTER]: " This script is called upon in the next one, which therefore exports its BROWSERS 8.2.4. File input and output continue exec fdN file ------------------------------------------------------------------------ script runs in the background. #!/bin/bash specified in days. echo "Tux don't like that. Tux wants fish!" [carol@octarine ~/test] ls -a a whole lot of support calls if it does not inform the user about what Received: (from anny@localhost) exit 1 order: will direct both standard input and standard error to the file If the line is empty, the items and the PS3 prompt are displayed again. michel ~> cat /var/tmp/fdtest.cron love 8.2.4.4. Here documents 9.6.1.1. Use of select From: Anny anny@octarine> ------------------------------------------------------------------------ *) no items are left in LIST. mkdir "$DESTDIR" [carol@octarine ~/test] rm * 8) echo -n "Enter your gender and press [ENTER]: " a script using the cron facility, the standard file descriptors are done files, compliant with a certain scheme, to PHP files. The conversion is anny ~/testdir> cat feed.sh opera pipes or other (temporary) files, unless some form of redirection is echo "On which topic do you want advice?" read ip1 name1 alias1 requires one argument, the year. Test that exactly one argument is mv $PICDIR/*.jpg "$DESTDIR"/ sleep 3600 ALTERNATE-CONSEQUENT-COMMANDS list, and the final command in the final echo date command. konqueror | \c | Suppress trailing newline. | case of one accidental overwrite, as is demonstrated in this test: 9.6.1.2. Examples ending. This is done when you don't know in advance how many times the to consider integrating some processing indication in the output of your within the same script. This is an example that installs a package # update fd 0 to target file /etc/passwd This is not a leap year. + continue # specific conversion script for my html files to php entered: + [[ TEST != *[[:upper:]]* ]] anny ~/testdir> date /dev/null, for instance when you just want a command to execute, no Running test transaction: 8.1. Displaying user messages Files are compressed before they are moved into the archive directory. hint for password: blue lagoon remove pictures from the previous months: Table 8-2. Options to the read built-in ;; 8.2.1. Using the read built-in command # You can now exit in a decent way. server." Use ps to check on processes. * If the standard output of a previous command is being piped to the Other people can now start executing the script: rm -rf "$i"; 8.2.2. Prompting for user input space=`df -h | awk '{print $5}' | grep % | grep -v Use | sort -n | tail -1 | cut -d "%" -f1 -` terminated with a newline character. The return status is always zero. LIST is expanded, generating a list of items. The expansion is printed is redirected. michel ~/test> feed.sh apple echo "This is a leap year. February has 29 days." QUIT="QUIT THIS PROGRAM - I feel safe now." #!/bin/bash to format output, see the Bash info pages. Keep in mind that there might michel ~> filter body.txt | cat header.txt /dev/fd/0 footer.txt | lp # This script opens 4 terminal windows. eventual causes of failure might get revealed. If you are not as lucky, fi *) while [ $HOUR -ne "00" ]; do * More flexible scripts can be built. because the child shell process will use the same file descriptors as 4. Edit the leaptest.sh script from [217]Section 7.2.4 so that it stderr, with file descriptor numbers 0, 1 and 2, respectively. These We stressed the importance of providing ample message for the users of read comment; echo $comment >> "$CONFIG" [7-8]*) Start thinking about cleaning out some stuff. There's a partition that is 87 % full. remote machine using scp. The script should report in a log file, * -e: interprets backslash-escaped characters. users. This construct can also be used to execute otherwise interactive HOUR=`date +%H` ;; done ------------------------------------------------------------------------ Enter your gender and press [ENTER] :m In this chapter we will discuss how to interact with the users of our bofh-excuses may be used by programmers to pass back different messages to the [1-6]*) else y |------------+---------------------------------------------------------| errors in your code. * Print a message informing the user about the size of the usage message. [anny@octarine tmp]$ friends.sh CASEN) COMMAND-LIST;; esac * Determine whether the backups directory has enough free space | | value (one or two hexadecimal digits). | 2. Do the same, using a case statement and an alternative use of the ------------------------------------------------------------------------ 9.4.2. Output redirection echo -e "*prrrrrrrt*\n" From the previous examples, it is clear that you can provide input and 7.5. Exercises space=`df -h | awk '{print $5}' | grep % | grep -v Use | sort -n | tail -1 | cut -d "%" -f1 -` Server: Fedora Linux 2 - i386 - core else command, the parent shell uses the current value of the $? variable. directory names. See the man page for more. The cat command first reads the file header.txt, next its standard input advised not to use it. allows for programs that use pathname arguments to handle standard input to standard error; each item is preceded by a number. If in LIST is not case EXPRESSION in CASE1) COMMAND-LIST;; CASE2) COMMAND-LIST;; ... TEST used to replace the shell of the current process or to alter the file michel ~> cat listdirs.sh Below is an example with a slightly adapted penguin.sh script, which if [[ "$name" != *[[:upper:]]* ]]; then $FORTUNE love michel ~/test> friends.sh Since child processes inherit open file descriptors, it is good practice Each case is an expression matching a pattern. The commands in the echo "You are added to Michel's friends list." echo "Guard: Buy the food that the Zoo provides for the animals, you ***, how cat /etc/hosts | grep -v "^#" > "$TEMP" case $space in ;; if [ "$animal" == "penguin" ]; then in the background or through the cron facility. More complex definitions executes until the TEST-COMMAND executes successfully. As long as this telling the user how many years he or she has to wait before legally 3) Note the use of the date command to generate all kinds of file and output files for a script (see [222]Section 8.2.4 for more), but some true. |------------+---------------------------------------------------------| 3) Enter comment or [ENTER] for no comment: hint for password: blue lagoon if [ $[$year % 100] -ne 0 ]; then Usage of the feed script: feed.sh food-on-menu animal-name command by themselves. do arithmetic. When prompting the user for input, it is also better to give too much time through the loop, NAME is set to the first item in LIST. The second with getting input from the user. for i in `ls /sbin`; do file /sbin/$i | grep ASCII; done ------------------------------------------------------------------------ +----------------------------------------------------------------------+ start echo The following is a specific application script for converting HTML Enter your name and press [ENTER]: anny 3. Modify /etc/profile so that you get a special greeting message when secondary groups. present, the positional parameters are printed, as if in $@ would have being allowed to drink. 5. Rewrite the script from [224]Section 7.2.1.4 so that it reads input if or elif clause has a non-zero exit status, then lr-x------ 1 michel michel 64 Jan 24 11:32 0 -> pipe:[124440] echo "Sports are a waste of time, energy and money." compressing the file. Possible choices could be gzip, bzip2, Note the initialization of the HOUR and DISKFULL variables and the use # create fd 7 with same target as fd 0 (save stdin "value") echo "Leaving..." exit 1 ;; else After a while, the friends list begins to look like this: echo "These are the web browsers on this system:" COMMAND-LIST for the first match are executed. The "|" symbol is used ls -l * 2> /var/tmp/unaccessible-in-spool | -d DELIM | The first character of DELIM is used to terminate the | generated by any command. The COMMANDS to execute can also be any education ;; esac init daemons are running on your system. If an httpd is running, the fi LIST="$(ls *.html)" When you run a script from the command line, nothing much changes the return status is zero. file1.xml file1.xml.bak file2.xml file2.xml.bak file3.xml file3.xml.bak From anny@octarine Tue Jan 14 22:10:47 2003 2) echo "At least one of my disks is nearly full!" | mail -s "daily diskcheck" root echo "That is not a valid choice, try a number from 0 to 10." on the other hand, execution resumes with TEST-COMMAND at the top of the ------------------------------------------------------------------------ Setting the PS3 prompt and adding a possibility to quit makes it better: * If the standard output of the current command is being piped to the |----------+-----------------------------------------------------------| echo "Pweepwishpeeterdepweet!" status) NEW=`echo $name | tr 'A-Z' 'a-z'` ------------------------------------------------------------------------ startrek 9.2.1. What is it? This small script can be used for simulation testing; it generates for anny@octarine>; Tue, 14 Jan 2003 22:10:47 +0100 ;; commands, as long as the command controlling the while loop executes 8.2.3.1. General The result is that you don't need to call on separate files; you can use The following options are supported by the Bash read built-in: stop | -r | escape character. The backslash is considered to be | Which colour of hair do you have? black environment. stop background information. file1.xml file2.xml file3.xml of options with ls and date in order to obtain a correct listing for ;; katya 22 blonde for setting us up such a great printing infrastructure. 8.2.4.1. Using /dev/fd * File descriptor closure "N>&-" has the effect of deleting the CONFIG=/var/tmp/sysconfig.out the file /dev/fd/N is equivalent to duplicating file descriptor N. If chmod go-rwx "$FILENAME" start # (use scp and SSH keys for a remote directory) As you know from basic shell usage, input and output of a command may be echo "Go back to your keyboard." ls -l * > /var/tmp/spoollist 2>&1 be executed upon input that causes break to be executed (when the user * Check /etc/passwd and decide on the first free user ID. Print a 5. Write a script called whichdaemon.sh that checks if the httpd and drink alcohol. If the user's age is below 16, print a message symbolic link /proc/self/fd/N. ------------------------------------------------------------------------ redirection operators - interpreted by the shell. Redirection may also | | than waiting for a complete line of input. | while [ $HOUR -ne "00" ]; do operating system commands, script, program or shell statement. The first generation. ;; SUM=$[$SUM + $SCORE] and "OR" (||). compressed backup. not delete) Michel's files. You can solve this problem using special Instead of using sed to replace the html suffix with php, it else ;; echo -n "How old are you? " parent using the exit 0 status. Upon failure, any other number may be Message="I seem to be running with an nonexistent amount of disk space..." 1) A simple if/then/fi test often preceeds commands in a shell script in echo "10. education" character may be used to remove any special meaning for the next facility. Do not forget to redirect output and errors when 9.4.1. Input redirection find "$PWD" -type f -a -mtime +5 | while read -d $'\000' file although you should be familiar with at least the use of echo by now, we Received: from octarine (localhost [127.0.0.1]) | | pair may not be used as a line continuation. | fi Test transaction complete, Success! 9.2.2.3. Using keyboard input to control the while loop echo "You are already registered, quitting." [231]Section 9.2.2.3. review the output file, or it may be used by another script as input. lrwxrwxrwx 1 root root 17 Oct 2 07:46 /dev/stdin -> proc/self/fd/0 will discuss some more examples in the next sections. 9[1-8]) [228]Warning Odd characters Feeding apple to camel... |------------+---------------------------------------------------------| Saving hosts information... SCORE="0" |----------+-----------------------------------------------------------| archive all together on your disk. If there is not enough diskspace, |----------+-----------------------------------------------------------| Introduction to Linux, chapter 9: "Preparing your data" for links done | -t TIMEOUT | line of input is not read within TIMEOUT seconds. This | ------------------------------------------------------------------------ returned. Based on the return code, the parent program can take jobs, that might not even be necessary when tests are inserted at the or her home directory. Implement the following features: Installed: tuxracer 0.61-26.i386 [carol@octarine ~/articles] ls *.xml respectively. 8.2.4.3. Closing file descriptors 127.0.0.1 localhost.localdomain localhost exec 6>&- You picked archive-20030129 (1) Guard: "Buy the food that the Zoo provides at the entry, you ***" Bash has the echo and printf commands to provide comments for users, and exit 2 echo "You picked $FILENAME ($REPLY), it is now only accessible to you." |------------+---------------------------------------------------------| echo |----------+-----------------------------------------------------------| ;; Enter your gender and press [ENTER] :f confuse. For the more complex conditionals, use the case syntax: This text is printed at the beginning of each print job and thanks the sysadmin The break statement is used to exit the current loop before its normal than too little information about the kind of data to be entered. This * Printing user friendly messages and explanations 2) As soon as the CONTROL-COMMAND fails, the loop exits. In a script, the while true; do querying system services. This is an excerpt of the script that starts This is a straightforward example, improving on the leaptest.sh script loop allows for specification of a list of values. A list of commands is # This script prints standard output unchanged, while standard error is + NEW=test ------------------------------------------------------------------------ successfully or if some other error occurred. | \0NNN | The eight-bit character whose value is the octal value | [227]Tip The basename command michel ~> ls -l /proc/self/fd/[0-2] echo -e "Tux don't like that. Tux wants fish!\n" Message="Start thinking about cleaning out some stuff. There's a partition that is $space % full." that makes a backup copy of each .xml file. After issuing the command, test that portion of code, rather than writing everything at once. tests for available disk space. If not enough disk space is available, | | the terminal or from a pipe. | ;; # (Cron version -- $Id: chap8.xml,v 1.9 2006/09/28 09:42:45 tille Exp $) | | Display PROMPT, without a trailing newline, before | our scripts. As always when others use your scripts, it is better to do while true; do michel ~> exec 4> result.txt exec 7&0 # This script will test if you have given a leap year or not. echo -e "Done feeding.\n" else michel ~/testdir> sysnotes.sh 1) else *) This is an example that you can put in your crontab for daily execution: not available on a system, you'll have to find a way to bypass the success of the child process. If no argument is given to the exit The exit statement takes an optional argument. This argument is the # This script installs packages automatically, using yum. 8.2.4.2.2. Read in scripts echo -n "Enter comment or [ENTER] for no comment: " # This script copies files from my homedirectory into the webserver directory. it is processed: if input is not within range, a message is printed. If | Option | Meaning | echo "6. magic" non-zero status, each elif list is executed in turn, and if its exit #!/bin/bash echo "On which topic do you want advice?" done NUM="0" Here is an example for the impatient: read ip2 name2 alias2 ;; fi ;; In nested loops, break allows for specification of which loop to exit. ------------------------------------------------------------------------ Although we talk about a here document, it is supposed to be a construct echo "Saving root account info..." explanation. | \a | Alert (bell). | added to the list, unless you are already in it. $FORTUNE kernelnewbies to close a file descriptor when it is no longer needed. This is done | \e | Escape. | # This script provides an easy way for users to choose between browsers. hour, a new directory is created, holding the images for that hour. netscape shell construct. echo been specified. LIST is only printed once. ------------------------------------------------------------------------ anny /etc/cron.daily> cat disktest.sh | \v | Vertical tab. | For convenience, errors are often redirected to /dev/null, if it is sure /etc/group and /etc/shadow; create the user's home directory # DO NOT EDIT THIS FILE - edit the master and reinstall. prompt for user input. This is usually done using the echo/read exec fdN> file # This script does a very simple test for checking disk space. case $? in while true; do In the example, we demonstrate use of cases for sending a more selective select FILENAME in *; This script has at least one disadvantage: it overwrites existing files. else read choice status is zero, the corresponding MORE-CONSEQUENT-COMMANDS is executed echo "3. kernelnewbies" useful to know about this kind of construction when executing heavy * Write scripts using the select statement. standard input of the current command, then * Redirection for the current command is processed from left to right. exit 1 ;; 7.2.2.2. Example Using this file descriptor might cause problems, see + LIST=test touch pic-`date +%s`.jpg # (/tmp/crontab.21968 installed on Fri Jan 24 11:30:41 2003) numbers and respective devices are reserved. Bash can take TCP or UDP executing the script always uses the desired options (cvp) and your system provides /dev/stdin, /dev/stdout and /dev/stderr, you will # This script lets you present different menus to Tux. He will only be happy | -a ANAME | array variable ANAME, starting at 0. All elements are | or updating the symbolic link /proc/self/fd/N with the target file. message. if test "x`pidof anacron`" != x; then 9.1.1. How does it work? elif [ $[$year % 4] -eq 0 ]; then ------------------------------------------------------------------------ the read command controlling a while loop: terminates execution of the entire script. It is most often used if the # A new directory is created every hour. string. the parent. When no such parent is available, for instance when you run matter what output or errors it gives. cat "$i" | sed -e '1,25d' | tac | sed -e '1,21d'| tac >> "$NEWNAME" occasion. FORTUNE=/usr/games/fortune # redirected for processing by awk. we are forcibly interrupted (with kill or Ctrl+C). Chapter 9. Repetitive tasks * Catching user input exit 1 Saving root account info... Fri Jan 24 11:05:50 CET 2003 Instead of controlling a loop by testing the result of a command or by NEWNAME=$(ls "$i" | sed -e 's/html/php/') Upon printing all the items, the PS3 prompt is printed and one line from scripts: exit 1 else case "$result" in CONFIRM to standard input, is closed each time the user needs to have access to a member. + ORIG=Test The until loop is very similar to the while loop, except that the loop commands TOREMOVE. konqueror more newlines wherever it appears. 8.2.4.2.1. Assigning file descriptors to files To: anny@octarine upon later on. Also, if you are lucky, errors will be mailed to you and requires input. The here document provides a way of instructing the 9.3.2. Example to assign a numeric value to a file. Instead of using the file name, you michel ~/testdir> cat sysnotes.sh applies to the checking of arguments and the accompanying usage message ------------------------------------------------------------------------ done ;; michel ~> cat startsurf.sh commands usually have a series of defined codes; see the programmer's echo "This is a leap year, February has 29 days." 8.4. Exercises significant. For example, this command, issued in /var/spool time, its value is set to the second item in the list, and so on. The Each clause must be terminated with ";;". Each case statement is ended + [[ test != *[[:upper:]]* ]] [http://www.tldp.org/LDP/intro-linux/html/sect_04_01.html#sect_04_01_06] If [in LIST] is not present, it is replaced with in $@ and for executes anny ~/testdir> cat disktest.sh Will you read this sign?! Don't feed the camels! * Gather information from the operator user: a comment describing for anny; Tue, 14 Jan 2003 22:10:47 +0100 about /proc subdirectories and the way your system handles standard file will redirect standard output of the ls command to the file This one lists the files in /sbin that are just plain text files, and REPLY. echo -e "\t\t\t\t -- \"Unhealthy is my middle name\" Soggie." lrwx------ 1 michel michel 64 Jan 23 12:11 /proc/self/fd/0 -> /dev/pts/6 * Using the file descriptors to read from and write to multiple $FORTUNE politics exec /etc/passwd * Ask the user whether a full or an incremental backup is wanted. Advanced Bash-Scripting Guide, chapter 16. You are strongly echo "$file archived" read topic 8.1.2. Using the echo built-in command 2) bash lynx # Calculate the average of a series of numbers. # monthly. #!/bin/bash descriptor is supplied as the argument to the -u option. the search string is found (no trailing blanks). All of the lines read | | option has no effect if read is not reading input from | The RESPECTIVE-COMMANDS are executed after each selection until the The tasks to execute in each case, such as stopping and starting the echo See info tar or descriptors for each running process. michel ~/test> feed.sh apple camel select FILENAME in *; 1) archive-20030129 if [ "$animal" == "penguin" ]; then number representing the break is read. This exits the loop. using file descriptors and redirection, and how this can be combined $feed $menu $animal fi input requested from the user is incorrect, if a statement did not run In this chapter, we learned how to provide user comments and how to character read and for line continuation. script should print a message like, "This machine is running a web mv $PICDIR/*.jpg "$DESTDIR"/ Guard: "You want to poison them, do you?" Of course, this situation is not ideal, since everybody can edit (but | -p PROMPT | attempting to read any input. The prompt is displayed | 7.2.4. Boolean operations read -n 1 gender file input and command line input: #!/bin/bash TEMP="/var/tmp/hosts.tmp" indication of how long the user will have to wait. If the waiting should 8.2.4.2. Read and exec anny 22 black ------------------------------------------------------------------------ be any list of words, strings or numbers, which can be literal or rm "$CONFIG" 2>/dev/null #!/bin/bash [carol@octarine ~/articles] ls *.xml > list fi 2000 ;; lrwxrwxrwx 1 root root 17 Oct 2 07:46 /dev/stderr -> proc/self/fd/2 lr-x------ 1 michel michel 64 Jan 24 11:32 3 -> /proc/21974/fd run or stop system processes. A theoretical example can be found in the you connect to your system as root. tend to forget about redirecting errors - output which might be depended grep -i "$name" "$friends" l-wx------ 1 michel michel 64 Jan 24 11:07 1 -> /var/tmp/fdtest.at3 [http://www.tldp.org/LDP/abs/html/io-redirection.html] the WEBDIR=/var/www/carol/webcam echo "Exiting." if [ $[$year % 400] -eq "0" ]; then input line into words or tokens; see [221]Section 3.4.8. The backslash 9.2.2.2. Nested while loops Gathering header information file(s) from server(s) Table 8-1. Escape sequences used by the echo command This text is printed at the beginning of each print job and thanks the sysadmin for separating multiple patterns, and the ")" operator terminates a directory that does not contain too much data. Write each step, then Text to be filtered. from the previous chapter: | | The words are assigned to sequential indexes of the | |------------+---------------------------------------------------------| or bzip2 for compressing the .tar file. Put all filenames in | | removed from ANAME before the assignment. Other NAME | The syntax for this loop is: echo "Disk space normal" | mail -s "daily diskcheck" root ports on networked hosts as file descriptors as well. in this chapter. When writing the scripts, you may test by using a test directs only the standard output to the destination file, because the echo "This script can make any of the files in this directory private." select WORD [in LIST]; do RESPECTIVE-COMMANDS; done done Figure 7-2. Example using Boolean operators michel ~/testdir> cat /var/tmp/sysconfig.out [install: tuxracer 0.61-26.i386] | | part of the line. In particular, a backslash-newline | for NAME [in LIST ]; do COMMANDS; done #!/bin/bash elif [ "$animal" == "dolphin" ]; then sleep 3600 Among other editors, gvim is one of those supporting colour schemes while CONTROL-COMMAND; do CONSEQUENT-COMMANDS; done command file order to prevent output generation, so that the script can easily be run # This script copies files from my homedirectory into the webserver directory. read colour echo -n "Which is your favorite? " preceding command. Using /dev/fd allows for uniformity and prevents command, or zero if none was executed. This script can make any of the files in this directory private. ------------------------------------------------------------------------ a simple at script: | | arguments are ignored. | else l-wx------ 1 michel michel 64 Jan 24 11:07 2 -> /var/spool/at/spool/a0000c010959eb Output will be saved in /var/tmp/sysconfig.out. sends its exit status back to the parent, feed.sh: else previous set of examples. It is also often combined with redirection to kernelnewbies by octarine (8.12.5/8.12.5) with ESMTP id h0ELAlBG020414 $FORTUNE literature shell-special characters, and it looks nicer than a bunch of echo's: "To:", "Subject:" and "From:" header lines. # This script acts upon the exit status given by penguin.sh echo "Average rating: $AVERAGE%." do they will not be needed. Hundreds of examples can be found in the more easily debugged. A script might do a perfect job, but you will get open files for a given process. These numeric values are known as file user. [carol@octarine ~/articles] for i in `cat list`; do cp "$i" "$i".bak ; done higher than 16, print a message saying that this user is allowed to echo "*prrrrrrrt*" character transformations. users don't have a clue which key combination is used for the EOF * Use the break and continue Bash built-ins. echo "Will you read this sign?!" These exercises are practical applications of the constructs discussed current month. The script should print the number of days in this Downloading needed headers # End here document ;; ls "$INPUTDIR"/* 2>&1 >&6 6>&- \ echo "You are added to Michel's friends list." echo "$ip2 $name2 $alias2" >> "$CONFIG" 8.1.1. Interactive or not? | \\ | Backslash. | Finding updated packages daemon, are defined in functions, which are partially sourced from the if (( ("$year" % 400) == "0" )) || (( ("$year" % 4 == "0") && ("$year" % 100 != maria 21 black Server: Fedora Linux 2 - i386 - freshrpms echo "Saving hosts information..." lr-x------ 1 michel michel 64 Jan 24 11:07 0 -> /var/spool/at/!0000c010959eb (deleted) while loop: alertvalue="80" as the first argument, since it might be interpreted as an option to the echo "OK, see you!" DESTDIR=$WEBDIR/"$DATE"/"$HOUR" i="0" $feed $menu $animal cat beginfile > "$NEWNAME" sequence, it is more user-friendly to have a break command as one of the anny ~/testdir> cat testleap.sh correct locations in a script, sparing system resources. "$QUIT") This script can be interrupted by the user when a Ctrl+C sequence is These are the web browsers on this system: anny ~/testdir> cat penguin.sh 2. Write a script that takes one file as an argument. Use a here ORIG="$name" This kind of redirection also works with other kinds of loops. The return status is the exit status of the last command executed in the else warning message with the disktest.sh script: lynx fi [214]Section 3.4.6. This is equivalent to the let statement. You will When writing interactive scripts, never hold back on comments. A script Message-Id: 200301142110.h0ELAltn020413@octarine> lrwx------ 1 michel michel 64 Jan 23 12:11 /proc/self/fd/2 -> /dev/pts/6 which is the output of the filter command, and last the footer.txt file. message containing this ID. 8.3. Summary Your local host configuration: ------------------------------------------------------------------------ | | only if input is coming from a terminal. | [carol@octarine ~/articles] ls *.xml* ;; |----------+-----------------------------------------------------------| Which is your favorite? opera | -s | Silent mode. If input is coming from a terminal, | that at any given moment you could have the data in your home Server: JPackage 1.5, generic q is pressed, the loop exits: Guard: You'd better give'm a fish, less they get violent... 9) michel ~/test> cat friends If no commands are executed because LIST does not expand to any items, construct. The return status is the exit status of the last CONSEQUENT-COMMANDS test test~ + echo 'new name for Test is test' | -n NCHARS | read returns after reading NCHARS characters rather | result="$?" read name i=$[$i+1] # fd 6 closed for current shell echo "Your local host configuration:" >> "$CONFIG" The following is a simple example redirecting only standard error to a mkdir $WEBDIR/"$DATE" Redirection can also occur in a script, so that it can receive input cat endfile >> "$NEWNAME" message that a full backup will be taken. In case of an *) conversion needs to be done, a continue statement restarts execution of else # This script provides wisdom while true; do lrwx------ 1 michel michel 64 Jan 23 12:11 /proc/self/fd/1 -> /dev/pts/6 The select construct allows easy menu generation. The syntax is quite ;; localhost. This requires SSH keys between the two hosts, or else you would be cleaner to use the basename command. Read the man page echo "This is not a leap year." Server: Fedora Linux 2 - i386 - updates 10) &> FILE Every day, a new directory is created containing 24 subdirectories. The Is this ok [y/N]: EnterDownloading Packages ;; ------------------------------------------------------------------------ shell's globbing feature, like this: ;; exec 0&7 7&- LIST="$(ls)" # This generates a file every 5 minutes * Create a private group for this user, checking the /etc/group # This script does a very simple test for checking disk space. echo -e "Usage of the feed script:\t$0 food-on-menu animal-name\n" esac The previous example is for the sake of demonstration. Regular |------------+---------------------------------------------------------| can, again, be any command that can exit with a success or failure 9.3. The until loop feed="/nethome/anny/testdir/penguin.sh" echo "Free advice on the topic of $topic: " Leaving... | -e | readline is used to obtain the line. | script. DESTDIR="$PWD/archive-$ARCHIVENR" document that presents the user with a couple of choices for gzip "$file"; mv "$file".gz "$DESTDIR" problem. This can be done for instance using a hyphen (-) to indicate The output below shows how the reserved file descriptors point to actual echo -n "Enter your choice, or 0 for exit: " ------------------------------------------------------------------------ [carol@octarine ~/test] touch test Test TEST Many scripts, however, require input from the user, or give output to incremental backup, only do this if the full backup is not [carol@octarine ~/testdir] cat archiveoldstuff.sh to one of the items, the value of WORD is set to the name of that item. Starting opera, please wait... as many levels of nested ifs as you can logically manage. #!/bin/bash lr-x------ 1 michel michel 64 Jan 24 11:07 3 -> /proc/21949/fd The script should use tar cf for the creation of the backup and gzip DISKFULL=$(df -h $WEBDIR | grep -v File | awk '{ print $5 }' | cut -d "%" -f1 -) echo "9. drugs" if [ "$animal" == "penguin" ]; then ------------------------------------------------------------------------ commands. The syntax of the read command is as follows: exec 7&0 |----------+-----------------------------------------------------------| get stuck using square brackets here, if you try something like $[$year case $FILENAME in it is safe to start working on your sources: Since the loop construct is considered to be one command structure (such Upon successful condition testing, the script can explicitly inform the read comment; echo $comment >> "$CONFIG" $FORTUNE bofh-excuses More about escape characters can be found in [220]Section 3.3.2. The When redirecting errors, note that the order of precedence is michel ~/test> cat feed.sh else + ORIG=TEST | Sequence | Meaning | exec 0&7 7&- that different actions can be undertaken upon success or failure of a if [ "$#" != "2" ]; then read [options] NAME1 NAME2 ... NAMEN elif [ "$animal" == "dolphin" ]; then * The script runs in a predictable way every time. fi ++ tr A-Z a-z echo -e "Guard: \"Buy the food that the Zoo provides at the entry, you ***\"\n" The read built-in command is the counterpart of the echo and printf esac do you think we survive?" * Test for the number of arguments. The script should run without I will do the following: +----------------------------------------------------------------------+ Tux don't like that. Tux wants fish! +----------------------------------------------------------------------+ mozilla cat topics echo $"Usage: $0 {start|stop|restart|condrestart|status}" |----------+-----------------------------------------------------------| with the esac statement. #!/bin/bash 9.2.2.4. Calculating an average anny ~/testdir> testleap.sh using scripts that are executed from your crontab! exits. fi Since we don't do a line count here, there is no way of knowing the line assigned to the first name, NAME1, the second word to the second name, 7.2.5. Using the exit statement and if for more info. executed for each value in the list. unaccessible-in-spool in /var/tmp. The command fi | | Cause read to time out and return failure if a complete | #!/bin/bash magic parent, so that different actions can be taken according to failure or Nested if statements might be nice, but as soon as you are confronted possibly scripts: the actual standard input device, usually the keyboard. [y/N]" string, the script answers "y" automatically: michel ~> cat /var/tmp/fdtest.at3 send it to the default printer. esac 9.2.2.1. Simple example using while Inside the if statement, you can use another if statement. You may use | | input line, rather than newline. | As you can see, exit status codes can be chosen freely. Existing fi # when given a fish. To make it more fun, we added a couple more animals. ;; Note that each process has its own view of the files under /proc/self, # fool-proof usage: the user as the script is running. The advantages of interactive scripts appropriate action. manual for each command for more information. This text is printed at the end of each print job. See the Bash info pages for more. ------------------------------------------------------------------------ echo "Your root account info:" >> "$CONFIG" syntax. In the above example, file descriptor 7, which has been assigned literature The above script can be shortened using the Boolean operators "AND" (&&) warning: commands will be executed using (in order) | | NNN (one to three octal digits). | echo "7. love" new name for TEST is test Anacron, a daemon that runs commands periodically with a frequency names containing spaces and other irregular characters. A * The script can report its progress as it runs. echo "5. bofh-excuses" variables menu and animal: #!/bin/bash read browser Return-Path: anny@octarine> ------------------------------------------------------------------------ SUID and SGID in the Introduction to Linux guide. integer exit status code, which is passed back to the parent and stored [carol@octarine ~/html] cat html2php.sh with two PHP tags that provide header and footer lines: if [ "$menu" == "fish" ]; then shell to read input from the current source until a line containing only michel ~> date command fails, the loop continues. The syntax is the same as for the while true; do redirection operators, as is demonstrated in the following example: init script directory. The startup scripts use start and stop cases to script or to make changes to it in the future. # If the pics are taking up too much space, the oldest are removed. echo -e "\a\a\aPweetpeettreetppeterdepweet!\a\a\a\n" target as the symbolic link /proc/self/fd/M. penguin.sh from [219]Section 7.2.1.2 a bit better: done February. 7.3.1. Simplified conditions 6) The return status is the exit status of the last command that executes. total 0 7.3. Using case statements for i in $PATHNAME/*; do 3. Write a script called homebackup that automates tar so the person *) 9.1.2.1. Using command substitution for specifying LIST items ++ tr A-Z a-z descriptors of the current shell. For example, it can be used to assign because a calculation is being done. If possible, try to give an echo -e "Feeding $menu to $animal...\n" give too much information than not enough. Here documents is a type of should occur after the done statement, so that it complies with the form more ideal construct to obtain the list would be to use the 4. Write a script called simple-useradd.sh that adds a local user to echo -e "Guard: \"No wonder they flee our planet...\"\n" | \n | Newline. | As we already explained previously, the ";" may be replaced with one or ------------------------------------------------------------------------ touch "$QUIT" echo "Exiting." done using the echo "1. politics" condrestart) done # This script lets you present different menus to Tux. He will only be happy have to supply a password. The creation of SSH keys is explained in In this clean example, all output is additionally piped through lp to # This script provides wisdom into many programs. There might also be problems when specifying hyphen 7. Adapt the script from the first example in [218]Section 7.3.1 to If no names are supplied, the line read is assigned to the variable for this account, extra groups of which the new user should be Note the use of the true statement. This means: continue execution until done descriptor has been assigned to a file, it can be used with the shell DATE=`date +%Y%m%d` [carol@octarine testdir] cat private.sh # This script creates a subdirectory in the current directory, to which old HOUR=`date +%H` echo "This script can make any of the files in this directory private." loop will have to execute, for instance because it is dependent on user echo -n "Which colour of hair do you have? " mkdir "$DESTDIR" echo -e "\a\a\a\a\a\aPweepwishpeeterdepweet!\a\a\a" for i in "$LIST"; do the standard input or standard output is a misconception that has crept #!/bin/bash 1) lrwxrwxrwx 1 root root 17 Oct 2 07:46 /dev/stdout -> proc/self/fd/1 start allows you to perform arithmetic and string comparisons, and testing of [223]Note File descriptor 5 michel ~/test> leaptest.sh You will run into problems if the list expands to file mkdir $WEBDIR/"$DATE" In the example below, output of the find command is used as input for done cat BROWSERS echo -e "Will you read this sign?! Don't feed the "$animal"s!\n" |----------+-----------------------------------------------------------| michel ~> at 1107 devices: Dependencies resolved spoollist. The command | \b | Backspace. | ------------------------------------------------------------------------ |----------+-----------------------------------------------------------| files: * Set the password for this user to a default known string. echo "new name for $ORIG is $NEW" 9.1. The for loop echo "8. literature" ls -l * 2 >& 1 > /var/tmp/spoollist | -u FD | Read input from file descriptor FD. | DATE=`date +%Y%m%d` automatically, eventhough you should normally confirm: break # A new directory is created every hour. as it is actually a symbolic link to /proc/process_ID>. until TEST-COMMAND; do CONSEQUENT-COMMANDS; done ;; can use the file descriptor number. The exec built-in command can be according to the file format; such editors are useful for detecting sleep 300 michel ~/test> cat leaptest.sh If this exists, remove it first in order to prevent output ;; A zero argument means that the script ran successfully. Any other value esac 8.2.3. Redirection and file descriptors * Redirection "N>&M" or "N&M" after a command has the effect of command. The actions can be determined using the if statement. This ------------------------------------------------------------------------ echo | awk 'BEGIN { FS=":" } { print "YOU HAVE NO ACCESS TO" $2 }' 6>&- FORTUNE=/usr/games/fortune | | NNN (zero to three octal digits). | echo "You picked $FILENAME ($REPLY)" Upon completion of this chapter, you will be able to The while construct allows for repetitive execution of a list of rm "$TEMP" #!/bin/bash if [ "$animal" == "penguin" ]; then * Users can customize the script as it runs or make it behave in failure status. The CONSEQUENT-COMMANDS can be any program, script or echo "2. startrek" commands continues. As soon as all the input lines are read the loop | \NNN | The eight-bit character whose value is the octal value | Done feeding. #!/bin/bash confusion: Message="I'm drowning here! There's a partition at $space %!" file. Print a message containing the group ID. If the user does not have a full backup file yet, print a anonymous pipe as /proc/previous_process_ID/fd/1. similar to that of the for loop: tille 24 black anny ~/testdir> tail -16 /var/spool/mail/anny likely, similar problems can be solved using sed and awk. However, it is michel ~> filter body.txt | cat header.txt /dev/fd/0 footer.txt >& 4 echo "Type the year that you want to check (4 digits), followed by [ENTER]:" + [[ Test != *[[:upper:]]* ]] user should enter. in the $? variable. echo -e "\a\a\aThanks for visiting the Zoo, hope to see you again soon!\n" as well. # using quotes to catch file names containing spaces, using read -d for more # This script makes an index of important config files, puts them together in + mv -b Test test backup destination directory (/var/backups) to make a backup of his with a couple of different possible actions to take, they tend to exec "$TEMP" netscape ARCHIVENR=`date +%Y%m%d` One line is read from the standard input, or from the file descriptor be used to open and close files for the current shell execution Tue Jan 14 20:37:55 CET 2003 michel ~/test> cat penguin.sh feed="/nethome/anny/testdir/penguin.sh" $FORTUNE startrek about the people Michel is interested in, but it will always say you are #!/bin/bash |----------+-----------------------------------------------------------| ------------------------------------------------------------------------ AVERAGE=$[$SUM / $NUM] of conditions are usually put in a case statement. +----------------------------------------------------------------------+ for setting us up such a great printing infrastructure. Initscripts often make use of case statements for starting, stopping and directory in a variable. This will make it easier to re-use the Test + mv -b TEST test job 10 at 2003-01-24 11:07 by octarine (8.12.5/8.12.5/Submit) id h0ELAltn020413 echo -e "Guard: \"You'd better give'm a fish, less they get violent...\"\n" echo "You are added to Michel's friends list. Thank you so much!" if [ $? == 0 ]; then anny ~/testdir> feed.sh apple penguin Some scripts run without any interaction from the user at all. 9.5.3. Examples month, and give information about leap years if the current month is [root@picon bin]# install.sh tuxracer * Take only one argument, or else exit after printing a usage #!/bin/bash Of course you could have opened your mail program to check the results; You are added to Michel's friends list. 7.2.3. Nested if statements fi [carol@octarine ~/test] bash -x tolower.sh webcam to a web directory. Every five minutes a picture is taken. Every read year echo "This is not a leap year. February has 28 days." anny ~/testdir> * With the obtained information, add a line to /etc/passwd, 32 11 * * * ls -l /proc/self/fd/ > /var/tmp/fdtest.cron 99) The read line is saved in the REPLY variable. status anacron anonymous pipe. #!/bin/bash during which the user might start worrying if no output appears for instance ~/log/homebackup.log. If you don't have a second + NEW=test When excuting a given command, the following steps are excuted, in The first is a command line example, demonstrating the use of a for loop We use the double brackets for testing an arithmetic expression, see #!/bin/bash user-friendly: ------------------------------------------------------------------------ |----------+-----------------------------------------------------------| from the user instead of taking it from the first argument. The example below was written to copy pictures that are made with a fi Server: JPackage 1.5 for Fedora Core 2 that the script is doing this, because it might take some time, Frequently, your script might call on another program or script that michel ~> filter body.txt.gz | cat header.txt - footer.txt ------------------------------------------------------------------------ The characters in the value of the IFS variable are used to split the In this chapter we learned how to build conditions into our scripts so # a backup file and allows for adding comment for each file. # This script acts upon the exit status given by penguin.sh Advantages of non-interactive scripts include: #!/bin/bash elif [ "$animal" == "dolphin" ]; then How old are you? 22 ------------------------------------------------------------------------ The script should also check for available diskspace. Keep in mind on the screen. As an example of adding comments, we will make the feed.sh and # This is a program that keeps your address book up to date. echo $rootpasswd >> "$CONFIG" #!/bin/bash loop terminates when NAME has taken on each of the values from LIST and The continue statement resumes iteration of an enclosing for, while, /etc/rc.d/init.d/functions file. See [216]Chapter 11 for more ;; The following example shows how you can use prompts to explain what the 7.3.2. Initscript example 6. Write a script that makes a backup of your home directory on a PS3="Your choice: " Subject: disk report Tue Jan 14 22:10:47 CET 2003 exit 2 # files are moved. input. politics michel ~/test> cat friends.sh 9.1.2.2. Using the content of a variable to specify LIST items tasks in the background, without intervention. Message="All is quiet." man ssh-keygen. shell construct that allows creation of lists, holding choices for the in central DNS * The script can run in the background. This is an example testing leap years: Note how the variables in the last lines are left unquoted in order to Enter the number of the file you want to protect: new name for Test is test ------------------------------------------------------------------------ export animal="$2" done The tr is part of the textutils package; it can perform all kinds of DESTDIR=$WEBDIR/"$DATE"/"$HOUR" #!/bin/bash The TEST-COMMANDS list is executed, and if its return status is zero, [225]Section 3.2.5 and [226]Section 7.2.1.2). esac export animal="$2" ALTERNATE-CONSEQUENT-COMMANDS is executed. The return status is the exit standard input of the next command, then + echo 'new name for TEST is test' CONSEQUENT-COMMANDS list, or zero if none was executed. TEST-COMMAND * Only now is the current command executed. michel ~/test> touch friends; chmod a+w friends successfully (exit status of zero). The syntax is: exit 3 # This script will test if we're in a leap year or not. In the following example, file names are converted to lower case. If no 0) echo -n "Enter your score [0-100%] ('q' for quit): "; read SCORE; as while TEST-COMMAND; do CONSEQUENT-COMMANDS; done), the redirection exit 1 Resolving dependencies echo "Guard: Don't forget the guide!" checks can easily be achieved using the system's cron fi character is encountered, if read times out or if an invalid file exit 1 echo "Hello, "$USER". This script will register you in Michel's friends database." the loop. These commands don't eat much system resources, and most drugs until or select loop. anny ~/testdir> fi startup scripts for your system. [http://tille.garrels.be/training/tldp/c4540.html#sect_09_01_01] Text to be filtered. An improved picturesort.sh script (see [230]Section 9.2.2.2), which You have new mail. We already briefly met the exit statement in [215]Section 7.2.1.3. It echo "Output will be saved in $CONFIG." acceptability, else exit printing a message), expiration date 1. Use an if/then/elif/else construct that prints information about the echo "Guard: You'd better give'm a fish, less they get violent..." # fd 1 targets pipe, fd 2 targets fd 1 target (pipe), echo -n "Make your choice: " root:x:0:0:root:/root:/bin/bash pipe: command following the done statement is executed. * The redirections "N> file" and "N file" have the effect of creating #? 1 --output omitted-- (with correct permissions!); add the user to the desired The example below demonstrates a while loop that can be interrupted. variables. Put the name of the remote server and the remote ;; if (("$SCORE" "0")) || (("$SCORE" > "100")); then $FORTUNE education 1. Write a script that asks for the user's age. If it is equal to or to the last name, NAMEN. If there are fewer words read from the input The following is an example that shows how you can alternate between yum install $1 CONFIRM Enter comment or [ENTER] for no comment: in central DNS l-wx------ 1 michel michel 64 Jan 24 11:32 1 -> /var/tmp/fdtest.cron |------------+---------------------------------------------------------| user input, you can specify a file from which to read input that anywhere, so that you can't start to do any worthwhile debugging. pattern list. Each case plus its according commands are called a clause. for name in "$LIST"; do combination. We also discussed how files can be used as input and output echo "Pweetpeettreetppeterdepweet!" next section. # Might be something for cron (if slightly adapted) to execute weekly or # when given a fish. We've also added a dolphin and (presumably) a camel. topics the COMMANDS once for each positional parameter that is set (see done 192.168.42.1 tintagel.kingarthur.com tintagel done Another way of looking at file descriptors is thinking of them as a way ------------------------------------------------------------------------ echo "This is not a leap year. February has 28 days." export menu="$1" |----------+-----------------------------------------------------------| up to that point are then used as the standard input for a command. As long as input lines are fed into the loop, execution of the loop #? 5) [carol@octarine testdir] private.sh echo "Guard: It's because of people like you that they are leaving earth all the time..." | | characters are not echoed. | files This is a slightly improved version of the wisdom.sh script from do sports status, and CONSEQUENT-COMMANDS can be any UNIX command, script or shell |------------+---------------------------------------------------------| stream than there are names, the remaining names are assigned empty stop * Compress the backup using any compression tool. Inform the user export menu="$1" if [ "$menu" == "fish" ]; then INPUTDIR="$1" The /dev/fd directory contains entries named 0, 1, 2, and so on. Opening fi #!/bin/bash As an extra, calculate how much beer an 18+ user has drunk a file descriptor to a file. Use a) $SHELL b) login shell c)/bin/sh again, the true test repeats the commands from the CONSEQUENT-COMMANDS * Use for, while and until loops, and decide which loop fits which 2) echo "Starting $browser, please wait..." the CONSEQUENT-COMMANDS list is executed. If TEST-COMMANDS returns a Chapter 8. Writing interactive scripts links /proc/current_process_ID>/fd/1 is updated to target another SUM="0" the next element in the list. When used in a while or until construct, Immediate_Placements :: Certified_Coders_Earn:_$30-$35K

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ViewPhotos of_Singles Near You at Match

ViewPhotos of_Singles Near You at MatchViewPhotos of_Singles Near You at Match anny ~/testdir> alertvalue="80" echo "These are the web browsers on this system:" status is zero, the corresponding MORE-CONSEQUENT-COMMANDS is executed # monthly. items. Any other value of the read line will set WORD to be a null Finding updated packages successfully or if some other error occurred. Some scripts run without any interaction from the user at all. Message="I'm drowning here! There's a partition at $space %!" warning message with the disktest.sh script: michel ~> exec 4> result.txt Each case is an expression matching a pattern. The commands in the users. This construct can also be used to execute otherwise interactive Note the use of the date command to generate all kinds of file and echo "8. literature" for setting us up such a great printing infrastructure. This is not a leap year. advised not to use it. done CONFIG=/var/tmp/sysconfig.out "To:", "Subject:" and "From:" header lines. shell-special characters, and it looks nicer than a bunch of echo's: #!/bin/bash The until loop is very similar to the while loop, except that the loop cat "$i" | sed -e '1,25d' | tac | sed -e '1,21d'| tac >> "$NEWNAME" #!/bin/bash echo -n "Which colour of hair do you have? " 8.2.3. Redirection and file descriptors echo -e "Guard: \"No wonder they flee our planet...\"\n" As we already explained previously, the ";" may be replaced with one or anny ~/testdir> date [carol@octarine ~/articles] for i in `cat list`; do cp "$i" "$i".bak ; done descriptors of the current shell. For example, it can be used to assign echo $Message | mail -s "disk report `date`" anny exit with an error message in the log file. The script should check for the existence of a compressed archive. lrwx------ 1 michel michel 64 Jan 23 12:11 /proc/self/fd/2 -> /dev/pts/6 | -t TIMEOUT | line of input is not read within TIMEOUT seconds. This | * Redirection "N>&M" or "N&M" after a command has the effect of start done # This script lets you present different menus to Tux. He will only be happy exec fdN file * Catching user input exec fdN> file | \\ | Backslash. | * Print a message informing the user about the size of the Instead of controlling a loop by testing the result of a command or by input line into words or tokens; see [221]Section 3.4.8. The backslash include the case of exactly 90% disk space usage, and lower than 10% for i in `ls /sbin`; do file /sbin/$i | grep ASCII; done until TEST-COMMAND; do CONSEQUENT-COMMANDS; done This text is printed at the beginning of each print job and thanks the sysadmin Resolving dependencies If no names are supplied, the line read is assigned to the variable michel ~> crontab -l echo "5. bofh-excuses" One line is read from the standard input, or from the file descriptor non-zero status, each elif list is executed in turn, and if its exit # This script will test if you have given a leap year or not. export menu="$1" break stop it is safe to start working on your sources: as while TEST-COMMAND; do CONSEQUENT-COMMANDS; done), the redirection echo "Free advice on the topic of $topic: " 9.1.2. Examples a simple at script: useful to know about this kind of construction when executing heavy fi NEW=`echo $name | tr 'A-Z' 'a-z'` mv $PICDIR/*.jpg "$DESTDIR"/ | \v | Vertical tab. | confuse. For the more complex conditionals, use the case syntax: regularly take a long time when executing a certain task, you might want parent using the exit 0 status. Upon failure, any other number may be ------------------------------------------------------------------------ The script should also check for available diskspace. Keep in mind [carol@octarine ~/testdir] cat archiveoldstuff.sh Test ;; * Use the break and continue Bash built-ins. different ways. read rootpasswd ;; do pipes or other (temporary) files, unless some form of redirection is # If the pics are taking up too much space, the oldest are removed. echo "$ip2 $name2 $alias2" >> "$CONFIG" * Set the password for this user to a default known string. l-wx------ 1 michel michel 64 Jan 24 11:32 2 -> pipe:[124441] esac ;; #!/bin/bash read colour directory in a variable. This will make it easier to re-use the month, and give information about leap years if the current month is higher than 16, print a message saying that this user is allowed to ++ tr A-Z a-z Nested if statements might be nice, but as soon as you are confronted 9.3.2. Example arguments. If any arguments are present, exit after printing a Server: Fedora Linux 2 - i386 - updates esac errors will cause your script to fail and won't be caught or sent that prints appropriate messages is much more user-friendly and can be to hold the backup. for assigning file descriptor N to file for output, and | -n NCHARS | read returns after reading NCHARS characters rather | *) Upon successful condition testing, the script can explicitly inform the In this chapter we will discuss how to interact with the users of our case $space in echo "Guard: Buy the food that the Zoo provides for the animals, you ***, how $browser & # A new directory is created every hour. ++ echo TEST appropriate action. michel ~/testdir> cat /var/tmp/sysconfig.out using file descriptors and redirection, and how this can be combined remove pictures from the previous months: echo "1. politics" echo "On which topic do you want advice?" 8.2. Catching user input [225]Section 3.2.5 and [226]Section 7.2.1.2). #? 1 The special meaning of the hyphen as a command-line argument to refer to loop. fi Note the initialization of the HOUR and DISKFULL variables and the use "$QUIT") if or elif clause has a non-zero exit status, then to format output, see the Bash info pages. Keep in mind that there might 9.5.1. The break built-in #!/bin/bash case "$1" in you connect to your system as root. anny ~/testdir> cat penguin.sh loop terminates when NAME has taken on each of the values from LIST and done This one lists the files in /sbin that are just plain text files, and echo -e "Usage of the feed script:\t$0 food-on-menu animal-name\n" # This script acts upon the exit status given by penguin.sh 2000 or her home directory. Implement the following features: case $choice in Enter your name and press [ENTER]: anny If the user does not have a full backup file yet, print a 5. Write a script called whichdaemon.sh that checks if the httpd and can use the file descriptor number. The exec built-in command can be echo "Go back to your keyboard." echo -n "Enter comment or [ENTER] for no comment: " if (( ("$year" % 400) == "0" )) || (( ("$year" % 4 == "0") && ("$year" % 100 != anny ~/testdir> cat testleap.sh 8.2.4.4. Here documents open files for a given process. These numeric values are known as file # (Cron version -- $Id: chap8.xml,v 1.9 2006/09/28 09:42:45 tille Exp $) 9.5. Break and continue and so on, with leftover words and their intervening separators assigned they will not be needed. Hundreds of examples can be found in the In the example, we demonstrate use of cases for sending a more selective You are added to Michel's friends list. echo $"Usage: $0 {start|stop|restart|condrestart|status}" echo "You are added to Michel's friends list." man ssh-keygen. fi done l-wx------ 1 michel michel 64 Jan 24 11:32 1 -> /var/tmp/fdtest.cron mv "$ORIG" "$NEW" 9.6. Making menus with the select built-in to standard input, is closed each time the user needs to have access to This text is printed at the beginning of each print job and thanks the sysadmin ++ tr A-Z a-z compress and zip. review the output file, or it may be used by another script as input. l-wx------ 1 michel michel 64 Jan 24 11:07 1 -> /var/tmp/fdtest.at3 | \r | Carriage return. | echo -e "Done feeding.\n" jobs, that might not even be necessary when tests are inserted at the script. chmod go-rwx "$FILENAME" # This script provides wisdom +----------------------------------------------------------------------+ Saving hosts information... more ideal construct to obtain the list would be to use the NUM="0" exit 2 $feed $menu $animal ls -l * 2 >& 1 > /var/tmp/spoollist that makes a backup copy of each .xml file. After issuing the command, echo "Enter the number of the file you want to protect:" konqueror by adding an echo command at the end of the script. This echo will also michel ~> at 1107 #!/bin/bash character read and for line continuation. The return status is the exit status of the last command that executes. done 9.1.1. How does it work? to the file whose name is the result of the expansion of FILE with this the CONSEQUENT-COMMANDS list is executed. If TEST-COMMANDS returns a michel ~/test> leaptest.sh NAME can be any variable name, although i is used very often. LIST can $FORTUNE politics fi * Using the file descriptors to read from and write to multiple command file echo -e "Guard: \"You'd better give'm a fish, less they get violent...\"\n" The example below was written to copy pictures that are made with a confusion: The read line is saved in the REPLY variable. If [in LIST] is not present, it is replaced with in $@ and for executes echo -e "\a\a\a\a\a\aPweepwishpeeterdepweet!\a\a\a" Start thinking about cleaning out some stuff. There's a partition that is 87 % full. echo "Your local host configuration:" >> "$CONFIG" In this chapter we learned how to build conditions into our scripts so % 400], because here, the square brackets don't represent an actual echo -e "Guard: \"You want to poison them, do you?\"\n" * Printing user friendly messages and explanations case "$result" in 8.4. Exercises #!/bin/bash | | arguments are ignored. | DESTDIR=$WEBDIR/"$DATE"/"$HOUR" Which colour of hair do you have? black Downloading needed headers loop will have to execute, for instance because it is dependent on user echo "Disk space normal" | mail -s "daily diskcheck" root 9.4. I/O redirection and loops michel ~/test> cat penguin.sh by octarine (8.12.5/8.12.5/Submit) id h0ELAltn020413 scripts: $feed $menu $animal The echo built-in command outputs its arguments, separated by spaces and ;; Upon completion of this chapter, you will be able to + echo 'new name for TEST is test' else The while construct allows for repetitive execution of a list of 9.6.1.2. Examples while true; do have to supply a password. The creation of SSH keys is explained in + [[ TEST != *[[:upper:]]* ]] echo "Exiting." 9.3. The until loop break echo HOUR=`date +%H` terminates execution of the entire script. It is most often used if the y target as the symbolic link /proc/self/fd/M. for anny; Tue, 14 Jan 2003 22:10:47 +0100 from a file, for instance, or send output to a file. Later, the user can $FORTUNE startrek construct: user. fi ports on networked hosts as file descriptors as well. &> FILE files: Setting the PS3 prompt and adding a possibility to quit makes it better: if [ "$animal" == "penguin" ]; then 8.2.3.2. Redirection of errors to the last name, NAMEN. If there are fewer words read from the input more newlines wherever it appears. ------------------------------------------------------------------------ * Prompting for user input | | Display PROMPT, without a trailing newline, before | 9.2.1. What is it? | | removed from ANAME before the assignment. Other NAME | backup destination directory (/var/backups) to make a backup of his tests for available disk space. If not enough disk space is available, Advanced Bash-Scripting Guide, chapter 16. You are strongly ------------------------------------------------------------------------ DISKFUL=$(df -h $WEBDIR | grep -v File | awk '{print $5 }' | cut -d "%" -f1 -) else done fi ------------------------------------------------------------------------ | \0NNN | The eight-bit character whose value is the octal value | be used to open and close files for the current shell execution if [[ "$name" != *[[:upper:]]* ]]; then WEBDIR=/var/www/carol/webcam compressing the file. Possible choices could be gzip, bzip2, failure status. The CONSEQUENT-COMMANDS can be any program, script or [carol@octarine ~/test] bash -x tolower.sh |------------+---------------------------------------------------------| ------------------------------------------------------------------------ You are added to Michel's friends list. The output below shows how the reserved file descriptors point to actual will discuss some more examples in the next sections. *) ------------------------------------------------------------------------ michel ~> cat listdirs.sh Your root account info: * With the obtained information, add a line to /etc/passwd, * The redirections "N> file" and "N file" have the effect of creating mkdir $WEBDIR/"$DATE" fi eventual causes of failure might get revealed. If you are not as lucky, names containing spaces and other irregular characters. A Thanks for visiting the Zoo, hope to see you again soon! ------------------------------------------------------------------------ esac Return-Path: anny@octarine> exec 6>&- maria 21 black ------------------------------------------------------------------------ michel ~/test> feed.sh apple executes until the TEST-COMMAND executes successfully. As long as this access modes on the script file, see [y/N]" string, the script answers "y" automatically: see that these are equivalent to /dev/fd/0, /dev/fd/1 and /dev/fd/2, descriptors for each running process. AVERAGE=$[$SUM / $NUM] | | characters are not echoed. | echo -e "*prrrrrrrt*\n" Using this file descriptor might cause problems, see Table 8-2. Options to the read built-in anonymous pipe. michel ~> date The following is a simple example redirecting only standard error to a again, the true test repeats the commands from the CONSEQUENT-COMMANDS command. The actions can be determined using the if statement. This exit 1 case EXPRESSION in CASE1) COMMAND-LIST;; CASE2) COMMAND-LIST;; ... directory, the data in the .tar file and the data in the compressed new name for Test is test variables menu and animal: | -a ANAME | array variable ANAME, starting at 0. All elements are | shell to read input from the current source until a line containing only * Write scripts that take a variable number of arguments. # DO NOT EDIT THIS FILE - edit the master and reinstall. In the example below, output of the find command is used as input for startrek # This is a program that keeps your address book up to date. |----------+-----------------------------------------------------------| while true; do 8.2.4.2.2. Read in scripts ------------------------------------------------------------------------ mv $PICDIR/*.jpg "$DESTDIR"/ drink alcohol. If the user's age is below 16, print a message done | | If this option is given, backslash does not act as an | [carol@octarine ~/articles] ls *.xml > list # This script opens 4 terminal windows. ------------------------------------------------------------------------ |------------+---------------------------------------------------------| 8.2.2. Prompting for user input /etc/group and /etc/shadow; create the user's home directory + mv -b Test test Since child processes inherit open file descriptors, it is good practice 32 11 * * * ls -l /proc/self/fd/ > /var/tmp/fdtest.cron ------------------------------------------------------------------------ gzip "$file"; mv "$file".gz "$DESTDIR" echo "Will you read this sign?!" # This script does a very simple test for checking disk space. for name in "$LIST"; do for instance ~/log/homebackup.log. If you don't have a second # Closes fd 6 for awk, but not for ls. lrwx------ 1 michel michel 64 Jan 23 12:11 /proc/self/fd/1 -> /dev/pts/6 file. Print a message containing the group ID. 3) private.sh echo "4. sports" #!/bin/bash |----------+-----------------------------------------------------------| while true; do 9.1.2.2. Using the content of a variable to specify LIST items or updating the symbolic link /proc/self/fd/N with the target file. generated by any command. The COMMANDS to execute can also be any 3) # Start here document because a calculation is being done. If possible, try to give an echo -n "How old are you? " | | input line, rather than newline. | anny ~/testdir> feed.sh apple penguin | | than waiting for a complete line of input. | netscape --output omitted-- * The script runs in a predictable way every time. CONSEQUENT-COMMANDS list, or zero if none was executed. TEST-COMMAND TOREMOVE. * Test for the number of arguments. The script should run without redirected before it is executed, using a special notation - the files, compliant with a certain scheme, to PHP files. The conversion is script should print a message like, "This machine is running a web #!/bin/bash These are the web browsers on this system: as many levels of nested ifs as you can logically manage. NUM=$[$NUM + 1] manual for each command for more information. the file /dev/fd/N is equivalent to duplicating file descriptor N. If In the following example, file names are converted to lower case. If no opera 9.2.2.4. Calculating an average status anacron The noclobber option to Bash is only useful when redirection occurs. The do echo "9. drugs" anny ~/testdir> tail -16 /var/spool/mail/anny user input, you can specify a file from which to read input that Enter comment or [ENTER] for no comment: in central DNS returned. Based on the return code, the parent program can take Every day, a new directory is created containing 24 subdirectories. The | \xHH | The eight-bit character whose value is the hexadecimal | Transaction(s) Complete spoollist. The command | -r | escape character. The backslash is considered to be | echo "Your root account info:" >> "$CONFIG" webcam to a web directory. Every five minutes a picture is taken. Every start Although we talk about a here document, it is supposed to be a construct init daemons are running on your system. If an httpd is running, the ------------------------------------------------------------------------ ++ ls the system. This script should: michel ~/testdir> sysnotes.sh Fri Jan 24 11:05:50 CET 2003 ------------------------------------------------------------------------ descriptor is supplied as the argument to the -u option. /proc/current_process_ID>/fd/0 is updated to target the same This script is called upon in the next one, which therefore exports its that at any given moment you could have the data in your home michel ~> filter body.txt | cat header.txt /dev/fd/0 footer.txt | lp string. touch "$QUIT" Dependencies resolved while CONTROL-COMMAND; do CONSEQUENT-COMMANDS; done The return code of the read command is zero, unless an end-of-file 7.5. Exercises Enter your name and press [ENTER]: michel lrwxrwxrwx 1 root root 17 Oct 2 07:46 /dev/stderr -> proc/self/fd/2 added to the list, unless you are already in it. echo 9.2.2. Examples DESTDIR="$PWD/archive-$ARCHIVENR" For convenience, errors are often redirected to /dev/null, if it is sure [214]Section 3.4.6. This is equivalent to the let statement. You will 7.3.1. Simplified conditions 1) done statistically (100 liters/year) and print this information for the case $? in If no commands are executed because LIST does not expand to any items, Guard: "Buy the food that the Zoo provides at the entry, you ***" lrwxrwxrwx 1 root root 17 Oct 2 07:46 /dev/stdin -> proc/self/fd/0 #!/bin/bash fi LIST="$(ls)" Message="Start thinking about cleaning out some stuff. There's a partition that is $space % full." Leaving... From anny@octarine Tue Jan 14 22:10:47 2003 [231]Section 9.2.2.3. space=`df -h | awk '{print $5}' | grep % | grep -v Use | sort -n | tail -1 | cut -d "%" -f1 -` executed for each value in the list. echo "You picked $FILENAME ($REPLY), it is now only accessible to you." # files are moved. | | The words are assigned to sequential indexes of the | if [ $age -lt 25 ]; then This is a slightly improved version of the wisdom.sh script from 7.2.5. Using the exit statement and if The following options are supported by the Bash read built-in: usage message. # This script provides wisdom Chapter 8. Writing interactive scripts Starting opera, please wait... until [ $DISKFUL -ge "90" ]; do read year descriptor has been assigned to a file, it can be used with the shell + echo 'new name for Test is test' #? Usage of the feed script: feed.sh food-on-menu animal-name The for loop is the first of the three shell looping constructs. This sleep 3600 * If the standard output of a previous command is being piped to the 6) After a while, the friends list begins to look like this: echo "This is not a leap year." matter what output or errors it gives. Hello, michel. This script will register you in Michel's friends database. fi echo "This script can make any of the files in this directory private." | | value (one or two hexadecimal digits). | message. Anacron, a daemon that runs commands periodically with a frequency cat beginfile > "$NEWNAME" cat BROWSERS The RESPECTIVE-COMMANDS are executed after each selection until the anny ~/testdir> cat feed.sh *) Running test transaction: while [ $HOUR -ne "00" ]; do michel ~/test> cat leaptest.sh total 0 | \f | Form feed. | This text is printed at the end of each print job. If an EOF (End Of File) character is read, the loop exits. Since most Other people can now start executing the script: # (/tmp/crontab.21968 installed on Fri Jan 24 11:30:41 2003) automatically, eventhough you should normally confirm: echo "$year is a leap year." elif [ "$animal" == "dolphin" ]; then Files are compressed before they are moved into the archive directory. # This script makes an index of important config files, puts them together in echo "You are added to Michel's friends list. Thank you so much!" 2000 is a leap year. 2) bash ------------------------------------------------------------------------ similar to that of the for loop: exit code, input and files needed by the script. redirection operators, as is demonstrated in the following example: 7.4. Summary message that a full backup will be taken. In case of an ------------------------------------------------------------------------ *) querying system services. This is an excerpt of the script that starts 192.168.42.1 tintagel.kingarthur.com tintagel 2. Do the same, using a case statement and an alternative use of the remote machine using scp. The script should report in a log file, supplied as an argument to the -u option. The first word of the line is We already briefly met the exit statement in [215]Section 7.2.1.3. It fi This is a very simple example, but as you can see, it is not very into many programs. There might also be problems when specifying hyphen This kind of redirection also works with other kinds of loops. read age feed="/nethome/anny/testdir/penguin.sh" michel ~> filter body.txt.gz | cat header.txt - footer.txt Each clause must be terminated with ";;". Each case statement is ended From the previous examples, it is clear that you can provide input and Text to be filtered. exit 1 ALTERNATE-CONSEQUENT-COMMANDS is executed. The return status is the exit as well. Many scripts, however, require input from the user, or give output to else ls "$INPUTDIR"/* 2>&1 >&6 6>&- \ cat endfile >> "$NEWNAME" SUM="0" #!/bin/bash | | the terminal or from a pipe. | next section. # This script converts all file names containing upper case characters into file# names containing only lower cases. allows you to perform arithmetic and string comparisons, and testing of Server: JPackage 1.5, generic stop) exit 2 9[1-8]) command: this is just to demonstrate that the script sends a decent mail with ------------------------------------------------------------------------ rm "$CONFIG" 2>/dev/null [1-6]*) mkdir "$DESTDIR" * File descriptor closure "N>&-" has the effect of deleting the archive all together on your disk. If there is not enough diskspace, As an example of adding comments, we will make the feed.sh and [carol@octarine testdir] private.sh successfully (exit status of zero). The syntax is: NEWNAME=$(ls "$i" | sed -e 's/html/php/') file1.xml file1.xml.bak file2.xml file2.xml.bak file3.xml file3.xml.bak echo "This is not a leap year. February has 28 days." The break statement is used to exit the current loop before its normal To: anny@octarine according to the file format; such editors are useful for detecting else In nested loops, break allows for specification of which loop to exit. This script can be interrupted by the user when a Ctrl+C sequence is number representing the break is read. This exits the loop. exit 3 numbers and respective devices are reserved. Bash can take TCP or UDP ;; can, again, be any command that can exit with a success or failure COMMAND-LIST for the first match are executed. The "|" symbol is used character may be used to remove any special meaning for the next $FORTUNE love #!/bin/bash echo This text is printed at the end of each print job. Of course you could have opened your mail program to check the results; exit 3 using scripts that are executed from your crontab! your system provides /dev/stdin, /dev/stdout and /dev/stderr, you will time through the loop, NAME is set to the first item in LIST. The second shell construct. # a backup file and allows for adding comment for each file. See info tar or |----------+-----------------------------------------------------------| DATE=`date +%Y%m%d` elif [ $[$year % 4] -eq 0 ]; then exec 7&0 ;; read ip2 name2 alias2 Here are some ideas to get you started using if in scripts: xterm & for setting us up such a great printing infrastructure. The main use of the /dev/fd files is from the shell. This mechanism Tux don't like that. Tux wants fish! not delete) Michel's files. You can solve this problem using special to close a file descriptor when it is no longer needed. This is done # fool-proof usage: test that portion of code, rather than writing everything at once. echo -n "Enter your gender and press [ENTER]: " * Create a private group for this user, checking the /etc/group else touch pic-`date +%s`.jpg The continue statement resumes iteration of an enclosing for, while, startup scripts for your system. SCORE="0" + mv -b TEST test 8.3. Summary server." Use ps to check on processes. used. This is demonstrated in the example below, which shows output from echo -n "Enter your score [0-100%] ('q' for quit): "; read SCORE; echo -e "\a\a\aPweetpeettreetppeterdepweet!\a\a\a\n" the standard input or standard output is a misconception that has crept anny 22 black to one of the items, the value of WORD is set to the name of that item. a file descriptor to a file. Use if [ $[$year % 400] -eq "0" ]; then # when given a fish. To make it more fun, we added a couple more animals. michel ~/test> feed.sh apple camel anny ~/testdir> testleap.sh [carol@octarine ~/html] cat html2php.sh You might want to check info MAKEDEV and info proc for more information elif [ "$animal" == "dolphin" ]; then facility. Do not forget to redirect output and errors when ------------------------------------------------------------------------ files l-wx------ 1 michel michel 64 Jan 24 11:07 2 -> /var/spool/at/spool/a0000c010959eb 8.2.4.2.1. Assigning file descriptors to files about the people Michel is interested in, but it will always say you are Gathering header information file(s) from server(s) Message-Id: 200301142110.h0ELAltn020413@octarine> |------------+---------------------------------------------------------| used to replace the shell of the current process or to alter the file commands. The syntax of the read command is as follows: elif [ "$gender" == "m" ]; then start |----------+-----------------------------------------------------------| 8.2.4.3. Closing file descriptors ;; exec fd&- politics exec 0&7 7&- /proc/current_process_ID>/fd/1 is updated to target another to standard error; each item is preceded by a number. If in LIST is not echo -n "Enter comment or [ENTER] for no comment: " ------------------------------------------------------------------------ When redirecting errors, note that the order of precedence is Received: (from anny@localhost) echo -e "Guard: \"Buy the food that the Zoo provides at the entry, you ***\"\n" sequence, it is more user-friendly to have a break command as one of the are, among others: 1) archive-20030129 done by taking out the first 25 and the last 21 lines, replacing these [228]Warning Odd characters # Read the first line of /etc/passwd anywhere, so that you can't start to do any worthwhile debugging. lr-x------ 1 michel michel 64 Jan 24 11:07 3 -> /proc/21949/fd requires input. The here document provides a way of instructing the done The cat command first reads the file header.txt, next its standard input # when given a fish. We've also added a dolphin and (presumably) a camel. more easily debugged. A script might do a perfect job, but you will get 9.3.1. What is it? Upon printing all the items, the PS3 prompt is printed and one line from Frequently, your script might call on another program or script that # first prepare a hosts file not containing any comments do # fd 1 targets pipe, fd 2 targets fd 1 target (pipe), ;; exit 1 The tasks to execute in each case, such as stopping and starting the during which the user might start worrying if no output appears echo "6. magic" [carol@octarine ~/articles] ls *.xml 8.1. Displaying user messages $FORTUNE kernelnewbies indication of how long the user will have to wait. If the waiting should The TEST-COMMANDS list is executed, and if its return status is zero, up to that point are then used as the standard input for a command. directory that does not contain too much data. Write each step, then And this is how the script runs. When prompted with the "Is this ok executing the script always uses the desired options (cvp) and ;; the search string is found (no trailing blanks). All of the lines read + [[ Test != *[[:upper:]]* ]] #!/bin/bash #!/bin/bash /etc/rc.d/init.d/functions file. See [216]Chapter 11 for more echo -e "Hmmmmmm fish... Tux happy!\n" and standard output in the same way as other pathnames. If /dev/fd is 3. Write a script called homebackup that automates tar so the person terminated with a newline character. The return status is always zero. | | Cause read to time out and return failure if a complete | variables. Put the name of the remote server and the remote echo "This script can make any of the files in this directory private." i="0" $FORTUNE bofh-excuses This is an example testing leap years: echo $rootpasswd >> "$CONFIG" DISKFULL=$(df -h $WEBDIR | grep -v File | awk '{ print $5 }' | cut -d "%" -f1 -) ;; else 3. Modify /etc/profile so that you get a special greeting message when How old are you? 22 michel ~> startsurf.sh ------------------------------------------------------------------------ from the previous chapter: This script has at least one disadvantage: it overwrites existing files. which is the output of the filter command, and last the footer.txt file. command fails, the loop continues. The syntax is the same as for the | \n | Newline. | read comment; echo $comment >> "$CONFIG" read choice ;; we are forcibly interrupted (with kill or Ctrl+C). for NAME [in LIST ]; do COMMANDS; done echo "You are added to Michel's friends list." echo "Sports are a waste of time, energy and money." secondary groups. * -n: suppresses the trailing newline. When you run a script from the command line, nothing much changes FORTUNE=/usr/games/fortune * Take only one argument, or else exit after printing a usage [227]Tip The basename command As an extra, calculate how much beer an 18+ user has drunk export menu="$1" [229]Note Use the system user should enter. case of one accidental overwrite, as is demonstrated in this test: # This generates a file every 5 minutes echo "10. education" the loop. These commands don't eat much system resources, and most ;; |----------+-----------------------------------------------------------| while true; do 8.2.4.1. Using /dev/fd |----------+-----------------------------------------------------------| lr-x------ 1 michel michel 64 Jan 24 11:32 3 -> /proc/21974/fd If the line is empty, the items and the PS3 prompt are displayed again. with two PHP tags that provide header and footer lines: echo "$ip1 $name1 $alias1" >> "$CONFIG" while true; do possibly scripts: 8.2.4.2. Read and exec | -u FD | Read input from file descriptor FD. | Note that no output is omitted here. The script only stores information 127.0.0.1 localhost.localdomain localhost by octarine (8.12.5/8.12.5) with ESMTP id h0ELAlBG020414 anny ~/testdir> cat disktest.sh echo "This is a leap year, February has 29 days." the next element in the list. When used in a while or until construct, construct. being allowed to drink. ;; unaccessible-in-spool in /var/tmp. The command be executed upon input that causes break to be executed (when the user These exercises are practical applications of the constructs discussed echo "Saving root account info..." I will do the following: lr-x------ 1 michel michel 64 Jan 24 11:07 0 -> /var/spool/at/!0000c010959eb (deleted) 1) exit 1 The tr is part of the textutils package; it can perform all kinds of ------------------------------------------------------------------------ disk space usage. And one with cron: echo -e "\a\a\aThanks for visiting the Zoo, hope to see you again soon!\n" * More flexible scripts can be built. | | option has no effect if read is not reading input from | 0) Guard: "You want to poison them, do you?" Enter comment or [ENTER] for no comment: hint for password: blue lagoon echo "*prrrrrrrt*" michel ~/testdir> cat sysnotes.sh following table gives an overview of sequences recognized by the echo 2) [install: tuxracer 0.61-26.i386] mozilla [http://www.tldp.org/LDP/abs/html/io-redirection.html] the # Might be something for cron (if slightly adapted) to execute weekly or current month. The script should print the number of days in this redirection operators - interpreted by the shell. Redirection may also QUIT="QUIT THIS PROGRAM - I feel safe now." standard error is copied to standard output before the standard output kernelnewbies echo -e "Will you read this sign?! Don't feed the "$animal"s!\n" |----------+-----------------------------------------------------------| love Table 8-1. Escape sequences used by the echo command no items are left in LIST. be any list of words, strings or numbers, which can be literal or The syntax for this loop is: if [ "$animal" == "penguin" ]; then 7.2.4. Boolean operations with the esac statement. conversion needs to be done, a continue statement restarts execution of A zero argument means that the script ran successfully. Any other value command by themselves. while [ $HOUR -ne "00" ]; do # This script provides an easy way for users to choose between browsers. #!/bin/bash From: Anny anny@octarine> This is the equivalent of > FILE 2>&1, the construct used in the bofh-excuses As soon as the CONTROL-COMMAND fails, the loop exits. In a script, the script or to make changes to it in the future. sleep 300 Enter the number of the file you want to protect: TOREMOVE=$(find $WEBDIR -type d -a -mtime +30) michel ~/test> cat feed.sh supplied. lynx shell's globbing feature, like this: success of the child process. If no argument is given to the exit for i in "$LIST"; do |------------+---------------------------------------------------------| | | NNN (one to three octal digits). | the actual standard input device, usually the keyboard. command, the parent shell uses the current value of the $? variable. result="$?" echo "Average rating: $AVERAGE%." present, the positional parameters are printed, as if in $@ would have [root@picon bin]# install.sh tuxracer echo "$name $age $colour" >> "$friends" echo "$file archived" incremental backup, only do this if the full backup is not ;; 9.6.1. General #!/bin/bash errors in your code. syntax. In the above example, file descriptor 7, which has been assigned friends="/var/tmp/michel/friends" read comment; echo $comment >> "$CONFIG" if [ $? == 0 ]; then Figure 7-2. Example using Boolean operators 7) SUM=$[$SUM + $SCORE] else drugs a script using the cron facility, the standard file descriptors are -b option to the mv command provides more security, but is only safe in * Determine whether the backups directory has enough free space a) $SHELL b) login shell c)/bin/sh The script should use tar cf for the creation of the backup and gzip elif [ "$animal" == "dolphin" ]; then You picked archive-20030129 (1) [carol@octarine testdir] cat private.sh DESTDIR=$WEBDIR/"$DATE"/"$HOUR" checks can easily be achieved using the system's cron echo "Guard: Don't forget the guide!" Done feeding. | -d DELIM | The first character of DELIM is used to terminate the | ------------------------------------------------------------------------ be differences between different versions of Bash. the COMMANDS once for each positional parameter that is set (see Advantages of non-interactive scripts include: CONFIRM Text to be filtered. else ------------------------------------------------------------------------ Enter your gender and press [ENTER] :m about /proc subdirectories and the way your system handles standard file from the user instead of taking it from the first argument. Introduction to Linux, chapter 9: "Preparing your data" for # specific conversion script for my html files to php at> EOT> |----------+-----------------------------------------------------------| else Is this ok [y/N]: EnterDownloading Packages exec "$TEMP" localhost. This requires SSH keys between the two hosts, or else you although you should be familiar with at least the use of echo by now, we echo "This is not a leap year. February has 28 days." mkdir "$DESTDIR" The following is an example that shows how you can alternate between ls -l * 2> /var/tmp/unaccessible-in-spool commands continues. As soon as all the input lines are read the loop 9.2.2.1. Simple example using while requires one argument, the year. Test that exactly one argument is * -e: interprets backslash-escaped characters. status) warning: commands will be executed using (in order) |------------+---------------------------------------------------------| with a couple of different possible actions to take, they tend to In this clean example, all output is additionally piped through lp to feed="/nethome/anny/testdir/penguin.sh" character transformations. give too much information than not enough. Here documents is a type of * Compress the backup using any compression tool. Inform the user standard input of the next command, then mozilla read name 1) ------------------------------------------------------------------------ Mind that break exits the loop, not the script. This can be demonstrated not available on a system, you'll have to find a way to bypass the while [ $i -lt 4 ] Message="I seem to be running with an nonexistent amount of disk space..." # using quotes to catch file names containing spaces, using read -d for more # This script installs packages automatically, using yum. yum install $1 CONFIRM * Check /etc/passwd and decide on the first free user ID. Print a tend to forget about redirecting errors - output which might be depended that the script is doing this, because it might take some time, cat topics telling the user how many years he or she has to wait before legally The return status is the exit status of the last CONSEQUENT-COMMANDS ls -l * > /var/tmp/spoollist 2>&1 fi as it is actually a symbolic link to /proc/process_ID>. 3) [carol@octarine ~/test] cat tolower.sh preceding command. Using /dev/fd allows for uniformity and prevents Feeding apple to camel... ;; ------------------------------------------------------------------------ echo "new name for $ORIG is $NEW" exit 1 | \t | Horizontal tab. | # fd 6 closed for current shell prompt for user input. This is usually done using the echo/read # This script does a very simple test for checking disk space. This small script can be used for simulation testing; it generates As long as input lines are fed into the loop, execution of the loop directs only the standard output to the destination file, because the within the same script. This is an example that installs a package # update fd 0 to target fd 7 target (old fd 0 target); delete fd 7 lr-x------ 1 michel michel 64 Jan 24 11:32 0 -> pipe:[124440] | Sequence | Meaning | CONTROL-COMMAND can be any command(s) that can exit with a success or michel ~/test> cat friends.sh pipe: Among other editors, gvim is one of those supporting colour schemes start) exec 6>&1 that different actions can be undertaken upon success or failure of a Many more examples using case statements can be found in your system's problem. This can be done for instance using a hyphen (-) to indicate standard input of the current command, then and "OR" (||). echo read -n 1 gender will direct both standard input and standard error to the file A here document is used to present the user with possible choices. And while loop: 2) ------------------------------------------------------------------------ # This script copies files from my homedirectory into the webserver directory. |----------+-----------------------------------------------------------| The script should clean up the compressed archive before it exits. | \e | Escape. | # End here document $FORTUNE literature (with correct permissions!); add the user to the desired # (use scp and SSH keys for a remote directory) stop rm "$TEMP" 7.3. Using case statements script runs in the background. echo "Pweetpeettreetppeterdepweet!" [carol@octarine ~/test] rm * Which is your favorite? opera if test "x`pidof anacron`" != x; then michel ~/test> friends.sh michel ~> ls -l /proc/self/fd/[0-2] ------------------------------------------------------------------------ find "$PWD" -type f -a -mtime +5 | while read -d $'\000' file Initscripts often make use of case statements for starting, stopping and | \c | Suppress trailing newline. | ;; else 5. Rewrite the script from [224]Section 7.2.1.4 so that it reads input number from which to start deleting lines until reaching the end. The user-friendly: penguin.sh from [219]Section 7.2.1.2 a bit better: Saving root account info... katya 22 blonde 3) michel ~> cat startsurf.sh echo "That is not a valid choice, try a number from 0 to 10." read browser export animal="$2" links if [ $# -lt 1 ]; then if [ "$animal" == "penguin" ]; then ------------------------------------------------------------------------ #!/bin/bash 9.2.2.2. Nested while loops | \a | Alert (bell). | This script calculates the average of user input, which is tested before else The result is that you don't need to call on separate files; you can use 9.2.2.3. Using keyboard input to control the while loop # fd 6 targets fd 1 target (console out) in current shell ending. This is done when you don't know in advance how many times the | -e | readline is used to obtain the line. | init script directory. The startup scripts use start and stop cases to if [ "$#" != "2" ]; then message containing this ID. + LIST=test ;; for assigning file descriptor N to file for input. After a file Another way of looking at file descriptors is thinking of them as a way Below is an example with a slightly adapted penguin.sh script, which 7.2.3. Nested if statements $FORTUNE drugs # update fd 0 to target file /etc/passwd daemon, are defined in functions, which are partially sourced from the # This script will test if we're in a leap year or not. is redirected. lrwxrwxrwx 1 root root 17 Oct 2 07:46 /dev/stdout -> proc/self/fd/1 stream than there are names, the remaining names are assigned empty 6. Write a script that makes a backup of your home directory on a Redirection can also occur in a script, so that it can receive input true. echo "On which topic do you want advice?" if [ "$space" -ge "$alertvalue" ]; then * Users can customize the script as it runs or make it behave in else select WORD [in LIST]; do RESPECTIVE-COMMANDS; done # This script creates a subdirectory in the current directory, to which old #!/bin/bash year=`date +%Y` status, and CONSEQUENT-COMMANDS can be any UNIX command, script or shell echo "Leaving..." to assign a numeric value to a file. Instead of using the file name, you if [ "$menu" == "fish" ]; then for anny@octarine>; Tue, 14 Jan 2003 22:10:47 +0100 For more information about the printf command and the way it allows you We stressed the importance of providing ample message for the users of output files for a script (see [222]Section 8.2.4 for more), but some done with getting input from the user. select FILENAME in *; #!/bin/bash command following the done statement is executed. February. | \NNN | The eight-bit character whose value is the octal value | echo "Hello, "$USER". This script will register you in Michel's friends database." +----------------------------------------------------------------------+ character is encountered, if read times out or if an invalid file read topic echo -e "Feeding $menu to $animal...\n" 10) *) explanation. the user as the script is running. The advantages of interactive scripts DATE=`date +%Y%m%d` # create fd 7 with same target as fd 0 (save stdin "value") When used in a for loop, the controlling variable takes on the value of if [ "$animal" == "penguin" ]; then As you know from basic shell usage, input and output of a command may be # A new directory is created every hour. new name for TEST is test Received: from octarine (localhost [127.0.0.1]) LIST="$(ls *.html)" file1.xml file2.xml file3.xml opera echo "Pweepwishpeeterdepweet!" for i in $PATHNAME/*; do | | part of the line. In particular, a backslash-newline | #!/bin/bash generation. on the screen. and the command completes. If else is followed by an using the creating or updating the symbolic link /proc/self/fd/N with the same Enter your gender and press [ENTER] :f exit 1 $FORTUNE $topic Bash allows for both standard output and standard error to be redirected +----------------------------------------------------------------------+ may be used by programmers to pass back different messages to the You have new mail. echo "Enter the number of the file you want to protect:" of conditions are usually put in a case statement. i=$[$i+1] echo -n "Which is your favorite? " a member. parent, so that different actions can be taken according to failure or |------------+---------------------------------------------------------| echo "Guard: You'd better give'm a fish, less they get violent..." |------------+---------------------------------------------------------| Of course, this situation is not ideal, since everybody can edit (but continue significant. For example, this command, issued in /var/spool combination. We also discussed how files can be used as input and output time, its value is set to the second item in the list, and so on. The # fd 1 targets fd 6 target (console out), fd 6 closed, execute ls pattern list. Each case plus its according commands are called a clause. echo "7. love" input. ------------------------------------------------------------------------ ------------------------------------------------------------------------ [carol@octarine ~/articles] ls *.xml* mkdir $WEBDIR/"$DATE" commands directory names. See the man page for more. it is processed: if input is not within range, a message is printed. If + continue You will run into problems if the list expands to file See the Bash info pages for more. commands usually have a series of defined codes; see the programmer's root:x:0:0:root:/root:/bin/bash cat /etc/hosts | grep -v "^#" > "$TEMP" in this chapter. When writing the scripts, you may test by using a test 4. Write a script called simple-useradd.sh that adds a local user to exec 7&0 michel ~/test> touch friends; chmod a+w friends exec 0&7 7&- ARCHIVENR=`date +%Y%m%d` An improved picturesort.sh script (see [230]Section 9.2.2.2), which problem is solved using tac, which reverses the lines in a file. 9.5.3. Examples echo if [ "$menu" == "fish" ]; then konqueror The read built-in command is the counterpart of the echo and printf 8) fi machine to copy the backup to, use scp to test copying it to the |----------+-----------------------------------------------------------| # This script acts upon the exit status given by penguin.sh sleep 3600 hour, a new directory is created, holding the images for that hour. for i in $TOREMOVE; do |----------+-----------------------------------------------------------| echo -e "Tux don't like that. Tux wants fish!\n" 5) echo #!/bin/bash 4. Edit the leaptest.sh script from [217]Section 7.2.4 so that it 4) order to prevent output generation, so that the script can easily be run esac Server: Fedora Linux 2 - i386 - core * Ask the user whether a full or an incremental backup is wanted. esac 8.2.1. Using the read built-in command symbolic link /proc/self/fd/N. * Gather information from the operator user: a comment describing Type the year that you want to check (4 digits), followed by [ENTER]: TEST [http://www.tldp.org/LDP/intro-linux/html/sect_04_01.html#sect_04_01_06] 99) allows for programs that use pathname arguments to handle standard input |----------+-----------------------------------------------------------| Server: Fedora Linux 2 - i386 - freshrpms that a program should read from a pipe. An example: [carol@octarine ~/test] ls -a respectively. ;; Installed: tuxracer 0.61-26.i386 9.2. The while loop until or select loop. 2. Write a script that takes one file as an argument. Use a here The following is a specific application script for converting HTML values. ;; When prompting the user for input, it is also better to give too much mkdir "$DESTDIR" Output will be saved in /var/tmp/sysconfig.out. done The return status is the exit status of the last command executed in the of options with ls and date in order to obtain a correct listing for REPLY. tuxracer 100 % done 1/1 our scripts. As always when others use your scripts, it is better to echo "You picked $FILENAME ($REPLY)" for this account, extra groups of which the new user should be status of the last command executed, or zero if no condition tested Note how the variables in the last lines are left unquoted in order to types "0"). * Use for, while and until loops, and decide which loop fits which than too little information about the kind of data to be entered. This + NEW=test done at> ls -l /proc/self/fd/ > /var/tmp/fdtest.at3 This is a straightforward example, improving on the leaptest.sh script If this exists, remove it first in order to prevent output The previous example is for the sake of demonstration. Regular |------------+---------------------------------------------------------| michel ~> ls -l /dev/std* sports read ip1 name1 alias1 echo "2. startrek" job 10 at 2003-01-24 11:07 to consider integrating some processing indication in the output of your ------------------------------------------------------------------------ compressed backup. ------------------------------------------------------------------------ 1. Write a script that asks for the user's age. If it is equal to or Test transaction complete, Success! LIST is expanded, generating a list of items. The expansion is printed esac echo The following example shows how you can use prompts to explain what the exits. ------------------------------------------------------------------------ send it to the default printer. 9.1.2.1. Using command substitution for specifying LIST items 9.5.2. The continue built-in When excuting a given command, the following steps are excuted, in topics done exit 1 | | only if input is coming from a terminal. | ALTERNATE-CONSEQUENT-COMMANDS list, and the final command in the final + ORIG=TEST stderr, with file descriptor numbers 0, 1 and 2, respectively. These if [ $[$year % 100] -ne 0 ]; then Instead of using sed to replace the html suffix with php, it We use the double brackets for testing an arithmetic expression, see ------------------------------------------------------------------------ ------------------------------------------------------------------------ do # You can now exit in a decent way. #!/bin/bash elif [ "$animal" == "dolphin" ]; then "0") )); then Server: JPackage 1.5 for Fedora Core 2 9.6.1.1. Use of select ;; been specified. LIST is only printed once. anny /etc/cron.daily> cat disktest.sh echo "Exiting." 2) test test~ The /dev/fd directory contains entries named 0, 1, 2, and so on. Opening ;; ;; entered: integer exit status code, which is passed back to the parent and stored # This script lets you present different menus to Tux. He will only be happy 8.1.2. Using the echo built-in command echo -e "\t\t\t\t -- \"Unhealthy is my middle name\" Soggie." echo "Hmmmmmm fish... Tux happy!" Inside the if statement, you can use another if statement. You may use get stuck using square brackets here, if you try something like $[$year ORIG="$name" BROWSERS A simple if/then/fi test often preceeds commands in a shell script in 7.3.2. Initscript example a whole lot of support calls if it does not inform the user about what echo "Guard: It's because of people like you that they are leaving earth all the time..." michel ~/test> cat friends in the background or through the cron facility. More complex definitions echo -n "Enter your name and press [ENTER]: " it is doing. So include messages that tell the user to wait for output ;; FORTUNE=/usr/games/fortune | \b | Backspace. | + ORIG=Test HOUR=`date +%H` devices: * Redirection for the current command is processed from left to right. Message="Better hurry with that new disk... One partition is $space % full." ;; fi date command. older than a week. or bzip2 for compressing the .tar file. Put all filenames in acceptability, else exit printing a message), expiration date on the other hand, execution resumes with TEST-COMMAND at the top of the PICSDIR=/home/carol/pics restart) [anny@octarine tmp]$ friends.sh do you think we survive?" ;; Since we don't do a line count here, there is no way of knowing the line The above script can be shortened using the Boolean operators "AND" (&&) literature Bash has the echo and printf commands to provide comments for users, and INPUTDIR="$1" fi #!/bin/bash HOUR=`date +%H` condrestart) done echo "Usage: $0 package." More about escape characters can be found in [220]Section 3.3.2. The loop allows for specification of a list of values. A list of commands is the read command controlling a while loop: would be cleaner to use the basename command. Read the man page The characters in the value of the IFS variable are used to split the echo "Be serious. Common, try again: " the return status is zero. ------------------------------------------------------------------------ in central DNS input requested from the user is incorrect, if a statement did not run 8.1.1. Interactive or not? likely, similar problems can be solved using sed and awk. However, it is grep -i "$name" "$friends" The select construct allows easy menu generation. The syntax is quite users don't have a clue which key combination is used for the EOF # This script copies files from my homedirectory into the webserver directory. * The script can run in the background. select FILENAME in *; #!/bin/bash for more info. 1. Use an if/then/elif/else construct that prints information about the standard input is read. If this line consists of a number corresponding ;; In this chapter, we learned how to provide user comments and how to break as the first argument, since it might be interpreted as an option to the Since the loop construct is considered to be one command structure (such done michel ~> cat /var/tmp/fdtest.cron michel ~> cat result.txt fi background information. command, or zero if none was executed. in the $? variable. lynx 7. Adapt the script from the first example in [218]Section 7.3.1 to [223]Note File descriptor 5 The exit statement takes an optional argument. This argument is the anny ~/testdir> tasks in the background, without intervention. occasion. | -p PROMPT | attempting to read any input. The prompt is displayed | q is pressed, the loop exits: echo "Starting $browser, please wait..." ;; export animal="$2" 8.2.4. File input and output * Write scripts using the select statement. * Only now is the current command executed. echo -e "Guard: \"Don't forget the guide!\"\n" education operating system commands, script, program or shell statement. The first echo "Tux don't like that. Tux wants fish!" ------------------------------------------------------------------------ echo -n "Make your choice: " elif [ "$SCORE" == "q" ]; then correct locations in a script, sparing system resources. assigned to the first name, NAME1, the second word to the second name, #!/bin/bash As you can see, exit status codes can be chosen freely. Existing echo "Type the year that you want to check (4 digits), followed by [ENTER]:" # redirected for processing by awk. Date: Tue, 14 Jan 2003 22:10:47 +0100 if (("$SCORE" "0")) || (("$SCORE" > "100")); then ------------------------------------------------------------------------ else because the child shell process will use the same file descriptors as CASEN) COMMAND-LIST;; esac chmod go-rwx "$FILENAME" | awk 'BEGIN { FS=":" } { print "YOU HAVE NO ACCESS TO" $2 }' 6>&- tille 24 black exit 1 This script can make any of the files in this directory private. michel ~> filter body.txt | cat header.txt /dev/fd/0 footer.txt >& 4 echo -n "Enter your choice, or 0 for exit: " Here is an example for the impatient: stop echo "You are already registered, quitting." $FORTUNE education ------------------------------------------------------------------------ This is an example that you can put in your crontab for daily execution: shell construct that allows creation of lists, holding choices for the file input and command line input: Subject: disk report Tue Jan 14 22:10:47 CET 2003 |----------+-----------------------------------------------------------| $FORTUNE magic environment. ;; previous set of examples. It is also often combined with redirection to Will you read this sign?! Don't feed the camels! SUID and SGID in the Introduction to Linux guide. will redirect standard output of the ls command to the file do arithmetic. netscape ;; AVERAGE="0" 7.2.2.2. Example Your local host configuration: | | NNN (zero to three octal digits). | michel ~/test> cp friends.sh /var/tmp; cd /var/tmp hint for password: blue lagoon ++ echo Test # This script prints standard output unchanged, while standard error is done Note that each process has its own view of the files under /proc/self, | -s | Silent mode. If input is coming from a terminal, | upon later on. Also, if you are lucky, errors will be mailed to you and run or stop system processes. A theoretical example can be found in the echo "Saving hosts information..." else Note the use of the true statement. This means: continue execution until #!/bin/bash echo "At least one of my disks is nearly full!" | mail -s "daily diskcheck" root echo "3. kernelnewbies" Message="All is quiet." ;; 9.1. The for loop |------------+---------------------------------------------------------| /dev/null, for instance when you just want a command to execute, no anonymous pipe as /proc/previous_process_ID/fd/1. [http://tille.garrels.be/training/tldp/c4540.html#sect_09_01_01] + [[ test != *[[:upper:]]* ]] sends its exit status back to the parent, feed.sh: +----------------------------------------------------------------------+ Guard: You'd better give'm a fish, less they get violent... TEMP="/var/tmp/hosts.tmp" ------------------------------------------------------------------------ space=`df -h | awk '{print $5}' | grep % | grep -v Use | sort -n | tail -1 | cut -d "%" -f1 -` *) ;; total 0 The first is a command line example, demonstrating the use of a for loop document that presents the user with a couple of choices for File input and output are accomplished by integer handles that track all rm -rf "$i"; PS3="Your choice: " [7-8]*) descriptors. The best known file descriptors are stdin, stdout and echo "OK, see you!" | | pair may not be used as a line continuation. | [carol@octarine ~/test] touch test Test TEST fi Hello, anny. This script will register you in Michel's friends database. exec /etc/passwd commands, as long as the command controlling the while loop executes Chapter 9. Repetitive tasks ------------------------------------------------------------------------ while true; do + NEW=test links applies to the checking of arguments and the accompanying usage message controls the loop. In such cases, read is often the controlling command. Tue Jan 14 20:37:55 CET 2003 list over and over again. read [options] NAME1 NAME2 ... NAMEN The example below demonstrates a while loop that can be interrupted. 8.2.3.1. General this user, choice from a list of shells (test for HOUR=`date +%H` # Calculate the average of a series of numbers. done michel ~> cat /var/tmp/fdtest.at3 fi echo "Output will be saved in $CONFIG." echo takes a couple of options: the parent. When no such parent is available, for instance when you run * The script can report its progress as it runs. lrwx------ 1 michel michel 64 Jan 23 12:11 /proc/self/fd/0 -> /dev/pts/6 case $FILENAME in 9.4.1. Input redirection 9) echo "This is a leap year. February has 29 days." | Option | Meaning | should occur after the done statement, so that it complies with the form ;; order: specified in days. 9.4.2. Output redirection * If the standard output of the current command is being piped to the magic When writing interactive scripts, never hold back on comments. A script for separating multiple patterns, and the ")" operator terminates a
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