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Full Discussion: I don't understand conditions :(
Top Forums UNIX for Dummies Questions & Answers I don't understand conditions :( Post 302568759 by hypsis on Friday 28th of October 2011 07:19:56 AM
Old 10-28-2011
Data I don't understand conditions :(
Hi there,
I have a very general question. I'm rather new to (bash) shell scripting and I don't understand how conditions work... I've read numerous tutorials but I don't get it. I really don't. Sometime what I do works, sometime it doesn't and that's frustating. So what's the actual difference between these three forms. I haven't so far been successful in using the last one - always get a "syntax error". As well, what are their operators ? When should you use "-eq" or "==" ?
Code:
if  [ ... ]               if [[ ... ]]               if (( ... ))

As an example, why does the first one works but not the second!?!
Code:
if [[ -n $a ]]          if [ -n $a ]

Also, how on Earth do you do stuff like (I know this doesn't work - but I've seen things alike) :
Code:
(( 2 > 1 )) && (( echo "2 > 1" ))

If you know where a nice tutorial exists on the matter, I'll be glad as well!
Many thanks
 

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LEARN ABOUT CENTOS

locale::codes::langvar

Locale::Codes::LangVar(3)				User Contributed Perl Documentation				 Locale::Codes::LangVar(3)

NAME

       Locale::Codes::LangVar - standard codes for language variation identification

SYNOPSIS

	  use Locale::Codes::LangVar;

	  $lvar = code2langvar('acm');		       # $lvar gets 'Mesopotamian Arabic'
	  $code = langvar2code('Mesopotamian Arabic'); # $code gets 'acm'

	  @codes   = all_langvar_codes();
	  @names   = all_langvar_names();

DESCRIPTION

       The "Locale::Codes::LangVar" module provides access to standard codes used for identifying language variations, 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 variations. 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:

	  $lvar = code2langvar('arevela','alpha');
	  $lvar = code2langvar('arevela',LOCALE_LANGVAR_ALPHA);

       The codesets currently supported are:

       alpha
	   This is the set of alphanumeric codes from the IANA language registry, such as 'arevela' for Eastern Armenian.

	   This code set is identified with the symbol "LOCALE_LANGVAR_ALPHA".

	   This is the default code set.

ROUTINES

       code2langvar ( CODE [,CODESET] )
       langvar2code ( NAME [,CODESET] )
       langvar_code2code ( CODE ,CODESET ,CODESET2 )
       all_langvar_codes ( [CODESET] )
       all_langvar_names ( [CODESET] )
       Locale::Codes::LangVar::rename_langvar  ( CODE ,NEW_NAME [,CODESET] )
       Locale::Codes::LangVar::add_langvar  ( CODE ,NAME [,CODESET] )
       Locale::Codes::LangVar::delete_langvar  ( CODE [,CODESET] )
       Locale::Codes::LangVar::add_langvar_alias  ( NAME ,NEW_NAME )
       Locale::Codes::LangVar::delete_langvar_alias  ( NAME )
       Locale::Codes::LangVar::rename_langvar_code  ( CODE ,NEW_CODE [,CODESET] )
       Locale::Codes::LangVar::add_langvar_code_alias  ( CODE ,NEW_CODE [,CODESET] )
       Locale::Codes::LangVar::delete_langvar_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 v5.16.3							    2013-04-12						 Locale::Codes::LangVar(3)
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