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Top Forums Shell Programming and Scripting evaluating a variable inside a variable Post 302578430 by rethink on Thursday 1st of December 2011 12:35:24 PM
Old 12-01-2011
evaluating a variable inside a variable

Hi there, i think im getting myself a little confused and need some help Smilie



I am reading in a bunch of variables to my script from an external file and need to validate that a value has been set for each

so if you can imagine, the user is required to pass in 4 values username,password,uid and gid. these get set to


$USER
$PASS
$UID
$GID

now this is fine, however I want to write a little loop that tests for its existence and echos an error if its not set. I appreciate I can do this as individual lines, but in reality there are more than 4 variables, there are hundreds, so id like to do it in a loop

so the idea being something like

Code:
 
for i in "USER PASS UID GID"; do
      if [ -z "$i" ] ; then
           echo $you have not entered a value for $i"
           exit 1
      fi
done

now i realise that this wont work because when $i is expanded it is just a string and not another varuable, but ive tried
Code:
 
 
if [ -z "${$i}" ] ; then

and
Code:
 
 
if [ -z "$${i}" ] ; then

etc

would I need to use 'eval' and if so, can someone give me an example of how i would do this?

any help would be greatly appreciated
 

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Locale::Codes::LangExt(3pm)				 Perl Programmers Reference Guide			       Locale::Codes::LangExt(3pm)

NAME
Locale::Codes::LangExt - standard codes for language extension identification SYNOPSIS
use Locale::Codes::LangExt; $lext = code2langext('acm'); # $lext gets 'Mesopotamian Arabic' $code = langext2code('Mesopotamian Arabic'); # $code gets 'acm' @codes = all_langext_codes(); @names = all_langext_names(); DESCRIPTION
The "Locale::Codes::LangExt" module provides access to standard codes used for identifying language extensions, such as those as defined in the IANA language registry. Most of the routines take an optional additional argument which specifies the code set to use. If not specified, the default IANA language registry codes will be used. SUPPORTED CODE SETS
There are several different code sets you can use for identifying language extensions. A code set may be specified using either a name, or a constant that is automatically exported by this module. For example, the two are equivalent: $lext = code2langext('acm','alpha'); $lext = code2langext('acm',LOCALE_LANGEXT_ALPHA); The codesets currently supported are: alpha This is the set of three-letter (lowercase) codes from the IANA language registry, such as 'acm' for Mesopotamian Arabic. This is the default code set. ROUTINES
code2langext ( CODE [,CODESET] ) langext2code ( NAME [,CODESET] ) langext_code2code ( CODE ,CODESET ,CODESET2 ) all_langext_codes ( [CODESET] ) all_langext_names ( [CODESET] ) Locale::Codes::LangExt::rename_langext ( CODE ,NEW_NAME [,CODESET] ) Locale::Codes::LangExt::add_langext ( CODE ,NAME [,CODESET] ) Locale::Codes::LangExt::delete_langext ( CODE [,CODESET] ) Locale::Codes::LangExt::add_langext_alias ( NAME ,NEW_NAME ) Locale::Codes::LangExt::delete_langext_alias ( NAME ) Locale::Codes::LangExt::rename_langext_code ( CODE ,NEW_CODE [,CODESET] ) Locale::Codes::LangExt::add_langext_code_alias ( CODE ,NEW_CODE [,CODESET] ) Locale::Codes::LangExt::delete_langext_code_alias ( CODE [,CODESET] ) These routines are all documented in the Locale::Codes::API man page. SEE ALSO
Locale::Codes The Locale-Codes distribution. Locale::Codes::API The list of functions supported by this module. http://www.iana.org/assignments/language-subtag-registry The IANA language subtag registry. AUTHOR
See Locale::Codes for full author history. Currently maintained by Sullivan Beck (sbeck@cpan.org). COPYRIGHT
Copyright (c) 2011-2013 Sullivan Beck This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.18.2 2013-11-04 Locale::Codes::LangExt(3pm)
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