---
name: "Perl::Critic::Policy::Compatibility::ProhibitUnixDevNull"
section: "3pm"
platform: "linux"
package: "libperl-critic-pulp-perl"
version: "99-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/Perl::Critic::Policy::Compatibility::ProhibitUnixDevNull"
---

# Perl::Critic::Policy::Compatibility::ProhibitUnixDevNull(3pm)

don't use explicit /dev/null

## NAME

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

## DESCRIPTION

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

*/dev/null*

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.

### Disabling

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),

```
    [-Compatibility::ProhibitUnixDevNull]
```

## SEE ALSO

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

## HOME PAGE

\<http://user42.tuxfamily.org/perl-critic-pulp/index.html\>

## COPYRIGHT

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 \<http://www.gnu.org/licenses/\>.