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Perl::Critic::Policy::Compatibility::ProhibitUnixDevNull(3pm) User Contributed Perl Documentation Perl::Critic::Policy::Compatibility::ProhibitUnixDevNull(3pm)


Perl::Critic::Policy::Compatibility::ProhibitUnixDevNull - don't use explicit /dev/null


This policy is part of the "Perl::Critic::Pulp" add-on. It ask you to not to use filename


explicitly, but instead "File::Spec->devnull()" for maximum portability across operating systems.

This policy is under the "maintenance" theme (see "POLICY THEMES" in Perl::Critic) on the basis that even if you're on a Unix system now you never know where your code might travel in the future.

"devnull()" is new in "File::Spec" version 0.8, so you should require that version (it's included in Perl 5.6.0 and up).

The checks for /dev/null are unsophisticated. A violation is reported for any string "/dev/null", possibly with an "open" style mode part, and any "qw" containing "/dev/null".

    open my $fh, '< /dev/null';                    # bad
    do_something ("/dev/null");                    # bad
    foreach my $file (qw(/dev/null /etc/passwd))   # bad

String comparisons are allowed because they're not uses of /dev/null as such but likely some sort of cross-platform check.

    if ($f eq '/dev/null') { ... }                 # ok
    return ($f ne '>/dev/null');                   # ok

/dev/null as just part of a string is allowed, including things like backticks and "system".

    print "Flames to /dev/null please\n"           # ok
    system ('rmdir /foo/bar >/dev/null 2>&1');     # ok
    $hi = `echo hi </dev/null`;                    # ok

Whether /dev/null is a good idea in such command strings depends what sort of shell you reach with that command and how much of Unix it might emulate on a non-Unix system.


If you only ever use a system with /dev/null or if everything else you write is hopelessly wedded to Unix anyway then you can disable "ProhibitUnixDevNull" from your .perlcriticrc in the usual way (see "CONFIGURATION" in Perl::Critic),



Perl::Critic::Pulp, Perl::Critic, File::Spec




Copyright 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2019, 2021 Kevin Ryde

Perl-Critic-Pulp is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

Perl-Critic-Pulp is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with Perl-Critic-Pulp. If not, see <>.

2021-02-28 perl v5.32.1