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.

   Disabling
       Most uses of "-f" tend to shell script style code written in Perl.  In the shell, it's usually not
       possible to do better than such tests (though "-d" or "-e" are still generally better than "-f"), but
       Perl can do the right thing.

       A blanket prohibition like this policy is harsh, but is meant as a building block or at least to make you
       think carefully whether "-f" is really right.  As always you can disable "ProhibitFiletest_f" from your
       .perlcriticrc in the usual way (see "CONFIGURATION" in Perl::Critic),

           [-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>.

perl v5.32.1                                 Perl::Critic::Policy::ValuesAndExpressions::ProhibitFiletest_f(3pm)