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

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