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ISBN : 978-2-7460-9712-4
EAN : 9782746097124
(Editions ENI)


CentOS 2.1AS







filetest − Perl pragma to control the filetest permission operators


    $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 permissions operators, the "−r" "−w" "−x" "−R" "−W" "−X" (see the perlfunc manpage).

The default behaviour 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 emulated.

NOTE : using the file tests for security purposes is a lost cause from the start: there is a window open for race conditions (who is to say that the permissions will not change between the test and the real operation?). Therefore if you are serious about security, just try the real operation and test for its success. Think atomicity.

subpragma access

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