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Full Discussion: test-and-set in bash
Top Forums Shell Programming and Scripting test-and-set in bash Post 302206412 by era on Tuesday 17th of June 2008 04:34:51 PM
Old 06-17-2008
Code:
: ${VAR:=something} ${ANOTHER:=whatever}

The semantics of the := variable substitution operator are not exactly equivalent to what you're asking about, but perhaps it's close enough.

Note that the default values are often set on a line which begins with the colon (basically "nop") shell command. It's different from the comment in that the rest of the line is evaluated by the shell. Anyway, see your shell's manual page for details.
 

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SURFRAW-UPDATE-PATH(1)					User Contributed Perl Documentation				    SURFRAW-UPDATE-PATH(1)

NAME
surfraw-update-path - updates PATH in shell config files SYNOPSIS
surfraw-update-path [-add] [-remove] [-check] [-sys] [-all] [-help] [-shell=SHELL] DESCRIPTION
surfraw-update-path adds the surfraw elvi directory (/usr/lib/surfraw) to your PATH in your shell's config file. Currently it supports bash, sh, csh, tcsh, ash, dash, ksh, pdksh, zsh, rc, and es Don't forget to login again or source your login files for it to take effect. OPTIONS
-check Checks to see if the surfraw config code is present. This is the default. -add Adds the surfraw config code. -remove Removes the surfraw config code -sys Updates the system-wide shell config instead of the user. Must be done as root. -shell=SHELL Selects the shell to configure. Defaults to the value of the $SHELL environment variable. Currently supported shells are: sh, ash, bash, dash, csh, tcsh, ksh, pdksh, zsh, rc, and es. -all Attempts to configure the startup files for all known shells -help Gives a usage message RETURN VALUE
-check returns 0 if the surfraw code is present in the file, 1 if it is not found, or 2 on error. All other options return 0 on success, or 2 on error. ENVIRONMENT
SHELL Used to determine which shell to configure, if -shell is not given. HOME Used to find users config files. ENV Used by posix-compliant shells to specify a startup rc file. ZDOTDIR Used to find user config files for zsh. If not set, defaults to HOME. SEE ALSO
surfraw(1), sh(1), ash(1), bash(1), dash(1), csh(1), tcsh(1), ksh(1), pdksh(1), zsh(1), rc(1), es(1) AUTHOR
Ian Beckwith <ianb@erislabs.net> perl v5.12.4 2011-07-12 SURFRAW-UPDATE-PATH(1)
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