filetest(3pm) Perl Programmers Reference Guide filetest(3pm)
NAME
filetest - Perl pragma to control the filetest permission operators
SYNOPSIS
$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
DESCRIPTION
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, how-ever, however,
ever, 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 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 2001-09-21 filetest(3pm)
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