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filetest(3p)     Perl Programmers Reference Guide    filetest(3p)

       filetest - Perl pragma to control the filetest permission

           $can_perhaps_read = -r "file";      # use the mode bits
               use filetest 'access';          # intuit harder
               $can_really_read = -r "file";
           $can_perhaps_read = -r "file";      # use the mode bits again

       This pragma tells the compiler to change the behaviour of
       the filetest permission operators, "-r" "-w" "-x" "-R"
       "-W" "-X" (see perlfunc).

       The default behaviour is to use the mode bits as returned
       by the stat() family of calls.  This, however, may not be
       the right thing to do if for example various ACL (access
       control lists) schemes are in use.  For such environments,
       "use filetest" may help the permission operators to return
       results more consistent with other tools.

       Each "use filetest" or "no filetest" affects statements to
       the end of the enclosing block.

       There may be a slight performance decrease in the
       filetests when "use filetest" is in effect, because in
       some systems the extended functionality needs to be emu-

       NOTE: using the file tests for security purposes is a lost
       cause from the start: there is a window open for race con-
       ditions (who is to say that the permissions will not
       change between the test and the real operation?).  There-
       fore if you are serious about security, just try the real
       operation and test for its success - think in terms of
       atomic operations.

       subpragma access

       Currently only one subpragma, "access" is implemented.  It
       enables (or disables) the use of access() or similar sys-
       tem calls.  This extended filetest functionality is used
       only when the argument of the operators is a filename, not
       when it is a filehandle.

perl v5.8.5                 2002-11-06                          1