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Full Discussion: Perl - backticks v system in if statements
Top Forums Shell Programming and Scripting Perl - backticks v system in if statements Post 79639 by tjlst15 on Friday 29th of July 2005 08:45:24 AM
Old 07-29-2005
Just a note, when using system in perl, it returns the exit code multiplied by 256. So, if a command returns 1, system("command") will return 256. So, to get the real return value, divide by 256.
 

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LEARN ABOUT CENTOS

perl::critic::policy::inputoutput::prohibitbacktickoperators

Perl::Critic::Policy::InputOutput::ProhibitBacktickOperaUser(Contributed Perl DocumPerl::Critic::Policy::InputOutput::ProhibitBacktickOperators(3)

NAME

       Perl::Critic::Policy::InputOutput::ProhibitBacktickOperators - Discourage stuff like "@files = `ls $directory`".

AFFILIATION

       This Policy is part of the core Perl::Critic distribution.

DESCRIPTION

       Backticks are super-convenient, especially for CGI programs, but I find that they make a lot of noise by filling up STDERR with messages
       when they fail.	I think its better to use IPC::Open3 to trap all the output and let the application decide what to do with it.

	   use IPC::Open3 'open3';
	   $SIG{CHLD} = 'IGNORE';

	   @output = `some_command`;			  #not ok

	   my ($writer, $reader, $err);
	   open3($writer, $reader, $err, 'some_command'); #ok;
	   @output = <$reader>;  #Output here
	   @errors = <$err>;	 #Errors here, instead of the console

CONFIGURATION

       Alternatively, if you do want to use backticks, you can restrict checks to void contexts by adding the following to your .perlcriticrc
       file:

	   [InputOutput::ProhibitBacktickOperators]
	   only_in_void_context = 1

       The purpose of backticks is to capture the output of an external command.  Use of them in a void context is likely a bug.  If the output
       isn't actually required, "system()" should be used.  Otherwise assign the result to a variable.

	   `some_command`;			#not ok
	   $output = `some_command`;		#ok
	   @output = `some_command`;		#ok

NOTES

       This policy also prohibits the generalized form of backticks seen as "qx{}".

       See perlipc for more discussion on using "wait()" instead of "$SIG{CHLD} = 'IGNORE'".

       You might consider using the "capture()" function from the IPC::System::Simple module for a safer way of doing what backticks do,
       especially on Windows.  The module also has a safe wrapper around "system()".

AUTHOR

       Jeffrey Ryan Thalhammer <jeff@imaginative-software.com>

COPYRIGHT

       Copyright (c) 2005-2011 Imaginative Software Systems.  All rights reserved.

       This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.  The full text of this license
       can be found in the LICENSE file included with this module.

perl v5.16.3							    2014-06-09	   Perl::Critic::Policy::InputOutput::ProhibitBacktickOperators(3)
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