Bash-Beginners-Guide

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Bash Guide for Beginners + echo 'Hi, willy!' Hi, willy! + echo + echo 'I will now fetch you a list of connected users:' I will now fetch you a list of connected users: + echo + w 4:50pm up 18 days, 6:49, 4 users, load average: 0.58, 0.62, 0.40 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT root tty2 - Sat 2pm 5:36m 0.24s 0.05s -bash willy :0 - Sat 2pm ? 0.00s ? - willy pts/3 - Sat 2pm 43:13 36.82s 36.82s BitchX willy ir willy pts/2 - Sat 2pm 43:13 0.13s 0.06s /usr/bin/screen + echo + echo 'I'\''m setting two variables now.' I'm setting two variables now. + COLOUR=black + VALUE=9 + echo 'This is a string: ' This is a string: + echo 'And this is a number: ' And this is a number: + echo + echo 'I'\''m giving you back your prompt now.' I'm giving you back your prompt now. + echo There is now a full-fledged debugger for Bash, available at SourceForge. These debugging features are available in most modern versions of Bash, starting from 3.x. 2.3.2. Debugging on part(s) of the script Using the set Bash built-in you can run in normal mode those portions of the script of which you are sure they are without fault, and display debugging information only for troublesome zones. Say we are not sure what the w command will do in the example commented-script1.sh, then we could enclose it in the script like this: set -x w set +x Output then looks like this: # activate debugging from here # stop debugging from here willy: ~/scripts> script1.sh The script starts now. Hi, willy! I will now fetch you a list of connected users: + w 5:00pm up 18 days, 7:00, 4 users, load average: 0.79, 0.39, 0.33 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT root tty2 - Sat 2pm 5:47m 0.24s 0.05s -bash willy :0 - Sat 2pm ? 0.00s ? - willy pts/3 - Sat 2pm 54:02 36.88s 36.88s BitchX willyke willy pts/2 - Sat 2pm 54:02 0.13s 0.06s /usr/bin/screen Chapter 2. Writing and debugging scripts 26
Bash Guide for Beginners + set +x I'm setting two variables now. This is a string: And this is a number: I'm giving you back your prompt now. willy: ~/scripts> You can switch debugging mode on and off as many times as you want within the same script. The table below gives an overview of other useful Bash options: Table 2-1. Overview of set debugging options Short notation Long notation Result set -f set -o noglob Disable file name generation using metacharacters (globbing). set -v set -o verbose Prints shell input lines as they are read. set -x set -o xtrace Print command traces before executing command. The dash is used to activate a shell option and a plus to deactivate it. Don't let this confuse you! In the example below, we demonstrate these options on the command line: willy:~/scripts> set -v willy:~/scripts> ls ls commented-scripts.sh script1.sh willy:~/scripts> set +v set +v willy:~/scripts> ls * commented-scripts.sh script1.sh willy:~/scripts> set -f willy:~/scripts> ls * ls: *: No such file or directory willy:~/scripts> touch * willy:~/scripts> ls * commented-scripts.sh script1.sh willy:~/scripts> rm * willy:~/scripts> ls commented-scripts.sh script1.sh Alternatively, these modes can be specified in the script itself, by adding the desired options to the first line shell declaration. Options can be combined, as is usually the case with UNIX commands: #!/bin/bash -xv Chapter 2. Writing and debugging scripts 27
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Bash Guide for Beginners 6.3.6. The
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Chapter 7. Conditional statements I
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Bash Guide for Beginners Table 7-2.
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Bash Guide for Beginners 7.1.2.2. N
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[root@elegance root]# We switch to
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Bash Guide for Beginners echo "Prop
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Bash Guide for Beginners We use the
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Bash Guide for Beginners case EXPRE
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Upon successful condition testing,
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Bash Guide for Beginners bit better
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8.2. Catching user input 8.2.1. Usi
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Bash Guide for Beginners michel ~/t
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Bash Guide for Beginners # DO NOT E
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File descriptor 5 Bash Guide for Be
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Bash Guide for Beginners The result
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Bash Guide for Beginners ♦ Compre
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Bash Guide for Beginners for i in `
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touch pic-`date +%s`.jpg sleep 300
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DISKFUL=$(df -h $WEBDIR | grep -v F
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;; 2) $FORTUNE startrek ;; 3) $FORT
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[carol@octarine ~/test] ls -a ./ ..
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Bash Guide for Beginners 9.7.2. Exa
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Chapter 10. More on variables In th
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Bash Guide for Beginners [bob in ~]
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if [ -z $1 ]; then echo "Usage: $0
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10.3.3. Transformations of variable
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Bash Guide for Beginners The opposi
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Chapter 11. Functions In this chapt
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The commands after && are only exec
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zip2 "$TAR" echo "...done." >> "$LO
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Chapter 12. Catching signals In thi
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Bash Guide for Beginners maud: ~> k
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Bash Guide for Beginners 2. Write a
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Bash Guide for Beginners jobs kill
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if [ $i -eq 5 ] ArrowUp+Enter or !!
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cd Change directory. cdp/cdplay An
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Bash Guide for Beginners gimp grep
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Send and receive mail. man Read man
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Bash Guide for Beginners rsh RPM Pa
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W Bash Guide for Beginners w Show w
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Index A aliases Section 3.5.1 ANSI-
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Bash Guide for Beginners Section 3.
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J Bash Guide for Beginners K kill k
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eadonly Section 10.1.3 regular expr
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Bash Guide for Beginners vi(m) Sect
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