filetest(3p) Perl Programmers Reference Guide filetest(3p)
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 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 condi-
tions (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 operations.
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.
perl v5.8.8 2005-02-05 1