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Top Forums Shell Programming and Scripting Bash parameter expansion from a config file Post 302515575 by Corona688 on Wednesday 20th of April 2011 12:19:01 PM
Old 04-20-2011
This doesn't work because bash doesn't substitute twice. If you have a string with "$varname" in it, it won't go back and start over and realize you also wanted $varname to be evaluated, too!

To do that kind of doublethink, you have to stuff it into an eval.

ARGS="$(eval $stringwithvarinit)"

Beware that you can do anything in an eval. Someone could stuff an `rm -rf ~/` in your config file and it could run it.
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UNIVERSAL::require(3)					User Contributed Perl Documentation				     UNIVERSAL::require(3)

NAME
UNIVERSAL::require - require() modules from a variable SYNOPSIS
# This only needs to be said once in your program. require UNIVERSAL::require; # Same as "require Some::Module" my $module = 'Some::Module'; $module->require or die $@; # Same as "use Some::Module" BEGIN { $module->use or die $@ } DESCRIPTION
If you've ever had to do this... eval "require $module"; to get around the bareword caveats on require(), this module is for you. It creates a universal require() class method that will work with every Perl module and its secure. So instead of doing some arcane eval() work, you can do this: $module->require; It doesn't save you much typing, but it'll make alot more sense to someone who's not a ninth level Perl acolyte. Methods require my $return_val = $module->require or die $@; my $return_val = $module->require($version) or die $@; This works exactly like Perl's require, except without the bareword restriction, and it doesn't die. Since require() is placed in the UNIVERSAL namespace, it will work on any module. You just have to use UNIVERSAL::require somewhere in your code. Should the module require fail, or not be a high enough $version, it will simply return false and not die. The error will be in $@ as well as $UNIVERSAL::require::ERROR. $module->require or die $@; use my $require_return = $module->use or die $@; my $require_return = $module->use(@imports) or die $@; Like "UNIVERSAL::require", this allows you to "use" a $module without having to eval to work around the bareword requirement. It returns the same as require. Should either the require or the import fail it will return false. The error will be in $@. If possible, call this inside a BEGIN block to emulate a normal "use" as closely as possible. BEGIN { $module->use } SECURITY NOTES
UNIVERSAL::require makes use of "eval STRING". In previous versions of UNIVERSAL::require it was discovered that one could craft a class name which would result in code being executed. This hole has been closed. The only variables now exposed to "eval STRING" are the caller's package, filename and line which are not tainted. UNIVERSAL::require is taint clean. COPYRIGHT
Copyright 2001, 2005 by Michael G Schwern <schwern@pobox.com>. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See http://www.perl.com/perl/misc/Artistic.html AUTHOR
Michael G Schwern <schwern@pobox.com> SEE ALSO
Module::Load, "require" in perlfunc, <http://dev.perl.org/rfc/253.pod> perl v5.16.2 2009-03-30 UNIVERSAL::require(3)
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