--- name: "Perl::Critic::Policy::ValuesAndExpressions::ProhibitFiletest_f" 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::ValuesAndExpressions::ProhibitFiletest_f" --- # Perl::Critic::Policy::ValuesAndExpressions::ProhibitFiletest\_f(3pm) don't use the -f file test ## 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)](/errno/3.md) ## 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 \.