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, 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  in
       Perl it is possible to do better.

       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 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 v5.30.0                                       2019-11-13             Perl::Critic::P...hibitFiletest_f(3pm)