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Manual Reference Pages  -  PERL::CRITIC::POLICY::INPUTOUTPUT::PROHIBITBACKTICKOPERATORS (3)

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NAME

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

CONTENTS

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.

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perl v5.20.3 PERL::CRITIC::POLICY::INPUTOUTPUT::PROHIBITBACKTICKOPERATORS (3) 2016-04-03

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