NAME¶

Perl::Critic::Policy::ValuesAndExpressions::ProhibitFiletest_f - don't use the -f file test

DESCRIPTION¶

This policy is part of the "Perl::Critic::Pulp" add-on. It asks you not to use the "-f" file test because doing so is usually wrong or unnecessarily restrictive. On that basis this policy is under the "bugs" theme and medium severity, see "POLICY THEMES" in Perl::Critic.

"-f" is not the opposite of "-d"

If you're traversing a tree and want to distinguish files from directories to descend into, then "-d" should be used so device files or named pipes can be processed.

    if (-f $filename) {      # bad
      process ($filename);
    } else {
      descend ($filename);
    }
    if (-d $filename) {      # better
      descend ($filename);
    } else {
      process ($filename);
    }
    

"-f" doesn't mean readable/writable/seekable

Char specials and named pipes are perfectly good for reading and writing, and char specials can support seeking. Demanding "-f" is an unnecessary restriction. You might only ever use ordinary files normally, but there's no need to prevent someone else running it on a tape drive, /dev/null, etc. You always have to test each seek() etc for success anyway, and that will tell you if a file is seekable.

    seek HANDLE, 123, 0
      or die "Cannot seek: $!";
    

"-e" is better than "-f"

A few inflexible functions or operations may not have good "file not found" behaviour and may force you to check for a file before invoking. Using "-e" is better than "-f" since as described above it doesn't unnecessarily disallow device files.

    if (-f $filename) {      # bad
      require $filename;
    }
    if (-e $filename) {      # better
      require $filename;
    }
    

"-f" before opening is a race condition

Testing a filename before opening is bad. Any test before opening is useless because the file can change or be removed in between the test and the open ("-X" in perlfunc, and "Consider this carefully" in filetest, note this about "-r" etc too).

    if (-f $filename) {               # bad
      open HANDLE, '<', $filename
    }
    

If you want to know if the file can be opened then open the file! The error return from open() must be checked, so a test beforehand only duplicates that, and is an opportunity to wrongly presume what the system or the user's permissions can or can't do.

When opening, "ENOENT" will say if there was no such file, or "EISDIR" if it's in fact a directory.

    if (! open HANDLE, '<', $filename) {  # better
      if ($! == POSIX::ENOENT()) {
        ...
      }
    }
    

If you really do want to enquire into the nature of the file, in order to only accept ordinary files, then open first and "-f" on the handle. But that's unusual except for an archiving or backup program.

Incidentally, the error message in $! is normally the best thing to print. It can be slightly technical, but its wording will at least be familiar from other programs and is translated into the user's locale language.

    [-ValuesAndExpressions::ProhibitFiletest_f]

SEE ALSO¶

Perl::Critic::Pulp, Perl::Critic, "open" in perlfunc, "ERRNO" in POSIX, Errno, errno(3)

HOME PAGE¶

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

COPYRIGHT¶

Copyright 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 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>.