Bash-Beginners-Guide

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Bash Guide for Beginners which -a script_name whereis script_name locate script_name 2.1.2. script1.sh In this example we use the echo Bash built-in to inform the user about what is going to happen, before the task that will create the output is executed. It is strongly advised to inform users about what a script is doing, in order to prevent them from becoming nervous because the script is not doing anything. We will return to the subject of notifying users in Chapter 8. Figure 2-1. script1.sh Write this script for yourself as well. It might be a good idea to create a directory ~/scripts to hold your scripts. Add the directory to the contents of the PATH variable: export PATH="$PATH:~/scripts" If you are just getting started with Bash, use a text editor that uses different colours for different shell constructs. Syntax highlighting is supported by vim, gvim, (x)emacs, kwrite and many other editors; check Chapter 2. Writing and debugging scripts 22
the documentation of your favorite editor. Different prompts The prompts throughout this course vary depending on the author's mood. This resembles much more real life situations than the standard educational $ prompt. The only convention we stick to, is that the root prompt ends in a hash mark (#). 2.1.3. Executing the script Bash Guide for Beginners The script should have execute permissions for the correct owners in order to be runnable. When setting permissions, check that you really obtained the permissions that you want. When this is done, the script can run like any other command: willy:~/scripts> chmod u+x script1.sh willy:~/scripts> ls -l script1.sh -rwxrw-r-- 1 willy willy 456 Dec 24 17:11 script1.sh willy:~> script1.sh The script starts now. Hi, willy! I will now fetch you a list of connected users: 3:38pm up 18 days, 5:37, 4 users, load average: 0.12, 0.22, 0.15 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT root tty2 - Sat 2pm 4:25m 0.24s 0.05s -bash willy :0 - Sat 2pm ? 0.00s ? - willy pts/3 - Sat 2pm 3:33m 36.39s 36.39s BitchX willy ir willy pts/2 - Sat 2pm 3:33m 0.13s 0.06s /usr/bin/screen I'm setting two variables now. This is a string: black And this is a number: 9 I'm giving you back your prompt now. willy:~/scripts> echo $COLOUR willy:~/scripts> echo $VALUE willy:~/scripts> This is the most common way to execute a script. It is preferred to execute the script like this in a subshell. The variables, functions and aliases created in this subshell are only known to the particular bash session of that subshell. When that shell exits and the parent regains control, everything is cleaned up and all changes to the state of the shell made by the script, are forgotten. If you did not put the scripts directory in your PATH, and . (the current directory) is not in the PATH either, you can activate the script like this: ./script_name.sh A script can also explicitly be executed by a given shell, but generally we only do this if we want to obtain special behavior, such as checking if the script works with another shell or printing traces for debugging: Chapter 2. Writing and debugging scripts 23
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Page 9 and 10: Introduction 1. Why this guide? The
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Page 21 and 22: Built-in commands are necessary to
Page 23 and 24: • Brace expansion • Tilde expan
Page 25 and 26: A number of methods can be used; on
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Page 37 and 38: Chapter 3. The Bash environment In
Page 39 and 40: Bash Guide for Beginners local pid
Page 41 and 42: MOZILLA_FIVE_HOME=/usr/lib/mozilla
Page 43 and 44: Bash Guide for Beginners franky ~>
Page 45 and 46: the GNU Awk programming language is
Page 47 and 48: Bash Guide for Beginners 3.2.4. Res
Page 49 and 50: LINES MACHTYPE MAILCHECK OLDPWD OPT
Page 51 and 52: two is the second positional parame
Page 53 and 54: Bash Guide for Beginners 3.3.1. Why
Page 55 and 56: A correctly-formed brace expansion
Page 57 and 58: Bash Guide for Beginners If the sub
Page 59 and 60: of the whitespace characters "space
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Page 65 and 66: Two regular expressions may be conc
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Page 73 and 74: sandy ~> sed -n '/a text/,/This/p'
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Page 79 and 80: Bash Guide for Beginners 121script.
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Bash Guide for Beginners amd.conf a
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Bash Guide for Beginners record1 re
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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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