lib/perl5/5.6.1/filetest.pm

   1 package filetest;
   2
   3 =head1 NAME
   4
   5 filetest - Perl pragma to control the filetest permission operators
   6
   7 =head1 SYNOPSIS
   8
   9     $can_perhaps_read = -r "file";      # use the mode bits
  10     {
  11         use filetest 'access';          # intuit harder
  12         $can_really_read = -r "file";
  13     }
  14     $can_perhaps_read = -r "file";      # use the mode bits again
  15
  16 =head1 DESCRIPTION
  17
  18 This pragma tells the compiler to change the behaviour of the filetest
  19 permissions operators, the C<-r> C<-w> C<-x> C<-R> C<-W> C<-X>
  20 (see L<perlfunc>).
  21
  22 The default behaviour to use the mode bits as returned by the stat()
  23 family of calls.  This, however, may not be the right thing to do if
  24 for example various ACL (access control lists) schemes are in use.
  25 For such environments, C<use filetest> may help the permission
  26 operators to return results more consistent with other tools.
  27
  28 Each "use filetest" or "no filetest" affects statements to the end of
  29 the enclosing block.
  30
  31 There may be a slight performance decrease in the filetests
  32 when C<use filetest> is in effect, because in some systems
  33 the extended functionality needs to be emulated.
  34
  35 B<NOTE>: using the file tests for security purposes is a lost cause
  36 from the start: there is a window open for race conditions (who is to
  37 say that the permissions will not change between the test and the real
  38 operation?).  Therefore if you are serious about security, just try
  39 the real operation and test for its success.  Think atomicity.
  40
  41 =head2 subpragma access
  42
  43 Currently only one subpragma, C<access> is implemented.  It enables
  44 (or disables) the use of access() or similar system calls.  This
  45 extended filetest functionality is used only when the argument of the
  46 operators is a filename, not when it is a filehandle.
  47
  48 =cut
  49
  50 $filetest::hint_bits = 0x00400000;
  51
  52 sub import {
  53     if ( $_[1] eq 'access' ) {
  54         $^H |= $filetest::hint_bits;
  55     } else {
  56         die "filetest: the only implemented subpragma is 'access'.\n";
  57     }
  58 }
  59
  60 sub unimport {
  61     if ( $_[1] eq 'access' ) {
  62         $^H &= ~$filetest::hint_bits;
  63     } else {
  64         die "filetest: the only implemented subpragma is 'access'.\n";
  65     }
  66 }
  67
  68 1;