filetest(3) Perl Programmers Reference Guide filetest(3)
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
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 function-
ality 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 in terms of atomic
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.
perl v5.8.6 2001-09-21 filetest(3)