Bash-Beginners-Guide

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Bash Guide for Beginners bash: 2: command not found franky ~> unset MYVAR1 first_name full_name franky ~> echo $MYVAR1 $first_name $full_name franky ~> 3.2.3. Exporting variables A variable created like the ones in the example above is only available to the current shell. It is a local variable: child processes of the current shell will not be aware of this variable. In order to pass variables to a subshell, we need to export them using the export built-in command. Variables that are exported are referred to as environment variables. Setting and exporting is usually done in one step: export VARNAME="value" A subshell can change variables it inherited from the parent, but the changes made by the child don't affect the parent. This is demonstrated in the example: franky ~> full_name="Franky M. Singh" franky ~> bash franky ~> echo $full_name franky ~> exit franky ~> export full_name franky ~> bash franky ~> echo $full_name Franky M. Singh franky ~> export full_name="Charles the Great" franky ~> echo $full_name Charles the Great franky ~> exit franky ~> echo $full_name Franky M. Singh franky ~> When first trying to read the value of full_name in a subshell, it is not there (echo shows a null string). The subshell quits, and full_name is exported in the parent - a variable can be exported after it has been assigned a value. Then a new subshell is started, in which the variable exported from the parent is visible. The variable is changed to hold another name, but the value for this variable in the parent stays the same. Chapter 3. The Bash environment 38
Bash Guide for Beginners 3.2.4. Reserved variables 3.2.4.1. Bourne shell reserved variables Bash uses certain shell variables in the same way as the Bourne shell. In some cases, Bash assigns a default value to the variable. The table below gives an overview of these plain shell variables: Table 3-1. Reserved Bourne shell variables Variable name CDPATH HOME IFS MAIL MAILPATH OPTARG OPTIND PATH PS1 PS2 Definition A colon-separated list of directories used as a search path for the cd built-in command. The current user's home directory; the default for the cd built-in. The value of this variable is also used by tilde expansion. A list of characters that separate fields; used when the shell splits words as part of expansion. If this parameter is set to a file name and the MAILPATH variable is not set, Bash informs the user of the arrival of mail in the specified file. A colon-separated list of file names which the shell periodically checks for new mail. The value of the last option argument processed by the getopts built-in. The index of the last option argument processed by the getopts built-in. A colon-separated list of directories in which the shell looks for commands. The primary prompt string. The default value is "'\s-\v\$ '". The secondary prompt string. The default value is "'> '". 3.2.4.2. Bash reserved variables These variables are set or used by Bash, but other shells do not normally treat them specially. Table 3-2. Reserved Bash variables Variable name auto_resume BASH BASH_ENV BASH_VERSION BASH_VERSINFO COLUMNS COMP_CWORD COMP_LINE COMP_POINT Definition This variable controls how the shell interacts with the user and job control. The full pathname used to execute the current instance of Bash. If this variable is set when Bash is invoked to execute a shell script, its value is expanded and used as the name of a startup file to read before executing the script. The version number of the current instance of Bash. A read-only array variable whose members hold version information for this instance of Bash. Used by the select built-in to determine the terminal width when printing selection lists. Automatically set upon receipt of a SIGWINCH signal. An index into ${COMP_WORDS} of the word containing the current cursor position. The current command line. Chapter 3. The Bash environment 39
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Page 9 and 10: Introduction 1. Why this guide? The
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Page 39 and 40: Bash Guide for Beginners local pid
Page 41 and 42: MOZILLA_FIVE_HOME=/usr/lib/mozilla
Page 43 and 44: Bash Guide for Beginners franky ~>
Page 45: the GNU Awk programming language is
Page 49 and 50: LINES MACHTYPE MAILCHECK OLDPWD OPT
Page 51 and 52: two is the second positional parame
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Page 73 and 74: sandy ~> sed -n '/a text/,/This/p'
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Bash Guide for Beginners We use the
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Bash Guide for Beginners case EXPRE
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Upon successful condition testing,
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Bash Guide for Beginners bit better
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8.2. Catching user input 8.2.1. Usi
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Bash Guide for Beginners michel ~/t
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Bash Guide for Beginners # DO NOT E
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File descriptor 5 Bash Guide for Be
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Bash Guide for Beginners The result
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Bash Guide for Beginners ♦ Compre
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Bash Guide for Beginners for i in `
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touch pic-`date +%s`.jpg sleep 300
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DISKFUL=$(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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