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# Copyright 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 Kevin Ryde |
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# Perl-Critic-Pulp is free software; you can redistribute it and/or modify |
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# it under the terms of the GNU General Public License as published by the |
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# Free Software Foundation; either version 3, or (at your option) any later |
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# version. |
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# |
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# Perl-Critic-Pulp is distributed in the hope that it will be useful, but |
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# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
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# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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# for more details. |
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# |
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# You should have received a copy of the GNU General Public License along |
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# with Perl-Critic-Pulp. If not, see <http://www.gnu.org/licenses/>. |
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package Perl::Critic::Policy::ValuesAndExpressions::ProhibitFiletest_f; |
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use 5.006; |
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use strict; |
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use warnings; |
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use base 'Perl::Critic::Policy'; |
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use Perl::Critic::Utils; |
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use Perl::Critic::Pulp; |
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our $VERSION = 98; |
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use constant supported_parameters => (); |
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use constant default_severity => $Perl::Critic::Utils::SEVERITY_MEDIUM; |
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use constant default_themes => qw(pulp bugs); |
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use constant applies_to => 'PPI::Token::Operator'; |
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sub violates { |
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my ($self, $elem, $document) = @_; |
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return if ($elem->content ne '-f'); |
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return $self->violation ("Don't use the -f file test", '', $elem); |
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} |
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1; |
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__END__ |
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=for stopwords seekable filename Ryde |
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=head1 NAME |
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Perl::Critic::Policy::ValuesAndExpressions::ProhibitFiletest_f - don't use the -f file test |
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=head1 DESCRIPTION |
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This policy is part of the L<C<Perl::Critic::Pulp>|Perl::Critic::Pulp> |
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add-on. It asks you not to use the C<-f> file test because doing so is |
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usually wrong or unnecessarily restrictive. On that basis this policy is |
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under the "bugs" theme and medium severity, see L<Perl::Critic/POLICY |
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THEMES>. |
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=over 4 |
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=item C<-f> is not the opposite of C<-d> |
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If you're traversing a tree and want to distinguish files from directories |
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to descend into, then C<-d> should be used so device files or named pipes |
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can be processed. |
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if (-f $filename) { # bad |
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process ($filename); |
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} else { |
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descend ($filename); |
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} |
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if (-d $filename) { # better |
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descend ($filename); |
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} else { |
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process ($filename); |
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} |
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=item C<-f> doesn't mean readable/writable/seekable |
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Char specials and named pipes are perfectly good for reading and writing, |
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and char specials can support seeking. Demanding C<-f> is an unnecessary |
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restriction. You might only ever use ordinary files normally, but there's |
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no need to prevent someone else running it on a tape drive, F</dev/null>, |
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etc. You always have to test each C<seek()> etc for success anyway, and |
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that will tell you if a file is seekable. |
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seek HANDLE, 123, 0 |
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or die "Cannot seek: $!"; |
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=item C<-e> is better than C<-f> |
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A few inflexible functions or operations may not have good "file not found" |
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behaviour and may force you to check for a file before invoking. Using |
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C<-e> is better than C<-f> since as described above it doesn't unnecessarily |
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disallow device files. |
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if (-f $filename) { # bad |
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require $filename; |
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} |
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if (-e $filename) { # better |
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require $filename; |
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} |
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=item C<-f> before opening is a race condition |
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Testing a filename before opening is bad. Any test before opening is |
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useless because the file can change or be removed in between the test and |
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the open (L<perlfunc/-X>, and L<filetest/Consider this carefully>, note this |
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about C<-r> etc too). |
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if (-f $filename) { # bad |
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open HANDLE, '<', $filename |
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} |
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If you want to know if the file can be opened then open the file! The error |
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return from C<open()> must be checked, so a test beforehand only duplicates |
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that, and is an opportunity to wrongly presume what the system or the user's |
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permissions can or can't do. |
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When opening, C<ENOENT> will say if there was no such file, or C<EISDIR> if |
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it's in fact a directory. |
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if (! open HANDLE, '<', $filename) { # better |
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if ($! == POSIX::ENOENT()) { |
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... |
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} |
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} |
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If you really do want to enquire into the nature of the file, in order to |
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only accept ordinary files, then open first and C<-f> on the handle. But |
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that's unusual except for an archiving or backup program. |
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Incidentally, the error message in C<$!> is normally the best thing to |
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print. It can be slightly technical, but its wording will at least be |
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familiar from other programs and is translated into the user's locale |
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language. |
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=back |
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=head2 Disabling |
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Most uses of C<-f> tend to shell script style code written in Perl. In the |
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shell, it's usually not possible to do better than such tests (though C<-d> |
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or C<-e> are still generally better than C<-f>), but Perl can do the right |
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thing. |
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A blanket prohibition like this policy is harsh, but is meant as a building |
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block or at least to make you think carefully whether C<-f> is really right. |
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As always you can disable C<ProhibitFiletest_f> from your F<.perlcriticrc> |
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in the usual way (see L<Perl::Critic/CONFIGURATION>), |
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[-ValuesAndExpressions::ProhibitFiletest_f] |
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=head1 SEE ALSO |
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L<Perl::Critic::Pulp>, |
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L<Perl::Critic>, |
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L<perlfunc/open>, |
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L<POSIX/ERRNO>, |
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L<Errno>, |
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L<errno(3)> |
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=head1 HOME PAGE |
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http://user42.tuxfamily.org/perl-critic-pulp/index.html |
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=head1 COPYRIGHT |
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Copyright 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 Kevin Ryde |
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Perl-Critic-Pulp is free software; you can redistribute it and/or modify it |
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under the terms of the GNU General Public License as published by the Free |
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Software Foundation; either version 3, or (at your option) any later |
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version. |
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Perl-Critic-Pulp is distributed in the hope that it will be useful, but |
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for |
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more details. |
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You should have received a copy of the GNU General Public License along with |
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Perl-Critic-Pulp. If not, see <http://www.gnu.org/licenses>. |
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=cut |