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Pro Bash Programming: Scripting the GNU/Linux Shell by Chris F. A. Johnson, Jayant Varma

By Chris F. A. Johnson, Jayant Varma

Pro Bash Programming teaches you ways to successfully make the most of the Bash shell on your programming. The Bash shell is a whole programming language, no longer basically a glue to mix exterior Linux instructions. via taking complete good thing about Shell internals, Shell courses can practice as snappily as utilities written in C or different compiled languages. and you may see how, with out assuming Unix lore, you could write specialist Bash 4.3 courses via general programming techniques.

This moment version has up to date for Bash 4.3, and plenty of scripts were rewritten to lead them to extra idiomatically Bash, taking higher good thing about positive aspects particular to Bash. you can actually learn, comprehend, and should train you the way to become familiar with Bash programming with out drowning you in pages and pages of syntax.

Using this booklet it is possible for you to to take advantage of the shell successfully, make scripts run quicker utilizing enlargement and exterior instructions, and know how to beat many universal errors that reason scripts to fail. This publication is ideal for all starting Linux and Unix procedure directors who are looking to be in complete keep watch over in their structures, and very become familiar with Bash programming.

What you’ll learn

  • Use the shell to jot down new utilities and attain such a lot programming tasks.
  • Use shell parameter enlargement to switch many exterior instructions, making scripts very fast.
  • Learn to prevent many universal error that reason scripts to fail.
  • Learn how Bash’s readline and heritage libraries can retailer typing whilst getting person input.
  • Learn to take advantage of good points new to Bash 4.0.
  • Build shell scripts that get details from the Web.

Who this e-book is for

Beginning Linux and Unix approach directors who are looking to be in complete command in their platforms.

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Additional resources for Pro Bash Programming: Scripting the GNU/Linux Shell

Example text

Sometimes, BASH_VERSION (or BASH_VERSINFO) is used to determine whether the running shell is capable of running a script. 0 to run this script" >&2; exit 2;; esac 45 Chapter 5 ■ Parameters and Variables The prompt string variables, PS1 and PS2, are used in interactive shells at the command line; PS3 is used with the select builtin command, and PS4 is printed before each line in execution trace mode (more on that in Chapter 10). SHELL VARIABLES The following variables are set by the shell: BASH BASHOPTS BASHPID BASH_ALIASES BASH_ARGC BASH_ARGV BASH_CMDS BASH_COMMAND BASH_EXECUTION_STRING BASH_LINENO BASH_REMATCH BASH_SOURCE BASH_SUBSHELL BASH_VERSINFO BASH_VERSION COMP_CWORD COMP_KEY COMP_LINE COMP_POINT COMP_TYPE COMP_WORDBREAKS COMP_WORDS COPROC DIRSTACK EUID FUNCNAME GROUPS HISTCMD HOSTNAME HOSTTYPE LINENO MACHTYPE MAPFILE OLDPWD OPTARG OPTIND OSTYPE PIPESTATUS PPID PWD RANDOM READLINE_LINE READLINE_POINT REPLY SECONDS SHELLOPTS SHLVL UID The following variables are used by the shell, which may set a default value for some of them (for example, IFS): BASH_COMPAT BASH_ENV BASH_XTRACEFD CDPATH CHILD_MAX COLUMNS COMPREPLY EMACS FCEDIT FIGNORE FUNCNEST GLOBIGNORE HISTCONTROL HISTFILE HISTFILESIZE HISTIGNORE HISTSIZE HISTTIMEFORMAT HOME HOSTFILE IFS IGNOREEOF INPUTRC LANG LC_ALL LC_COLLATE LC_CTYPE LC_MESSAGES LC_NUMERIC LC_NUMERIC LINES MAIL MAILCHECK MAILPATH OPTERR PATH POSIXLY_CORRECT PROMPT_COMMAND PROMPT_DIRTRIM PS1 PS2 PS3 PS4 SHELL TIMEFORMAT TMOUT TMPDIR auto_resume histchars See Appendix A for a description of all the shell variables.

Consecutive quoted words without any intervening whitespace are considered as a single argument: $ sa "First argument "'still the first argument' :First argument still the first argument: In bash, single quotes can be included in words of the form $'string' if they are escaped. In addition, the escape sequences listed in Chapter 2’s description of printf are replaced by the characters they represent: $ echo $'\'line1\'\n\'line2\'' 'line1' 'line2' 30 Chapter 4 ■ Command-Line Parsing and Expansion Quoted arguments can contain literal newlines: $ sa "Argument containing ⏎ > a newline" :Argument containing a newline: ■■Note The ⏎ is the enter key and not something to be typed on the terminal.

It stores the results in three variables: _MIN3, _MID3, and _MAX3. Listing 6-5. _max3, Sort Three Integers _max3() #@ Sort 3 { #@ USAGE: [ $# -ne 3 ] [ $1 -gt $2 ] [ $2 -gt $3 ] [ $1 -gt $2 ] _MAX3=$3 _MID3=$2 _MIN3=$1 } integers and store in $_MAX3, $_MID3 and $_MIN3 && && && && return 5 { set -- $2 $1 $3; } { set -- $1 $3 $2; } { set -- $2 $1 $3; } 63 Chapter 6 ■ Shell Functions In the first edition of this book, I used the convention of beginning function names with an underscore when they set a variable rather than print the result.

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