1filetest(3pm)          Perl Programmers Reference Guide          filetest(3pm)
2
3
4

NAME

6       filetest - Perl pragma to control the filetest permission operators
7

SYNOPSIS

9           $can_perhaps_read = -r "file";      # use the mode bits
10           {
11               use filetest 'access';          # intuit harder
12               $can_really_read = -r "file";
13           }
14           $can_perhaps_read = -r "file";      # use the mode bits again
15

DESCRIPTION

17       This pragma tells the compiler to change the behaviour of the filetest
18       permission operators, "-r" "-w" "-x" "-R" "-W" "-X" (see perlfunc).
19
20       The default behaviour is to use the mode bits as returned by the stat()
21       family of calls.  This, however, may not be the right thing to do if
22       for example various ACL (access control lists) schemes are in use.  For
23       such environments, "use filetest" may help the permission operators to
24       return results more consistent with other tools.
25
26       Each "use filetest" or "no filetest" affects statements to the end of
27       the enclosing block.
28
29       There may be a slight performance decrease in the filetests when "use
30       filetest" is in effect, because in some systems the extended function‐
31       ality needs to be emulated.
32
33       NOTE: using the file tests for security purposes is a lost cause from
34       the start: there is a window open for race conditions (who is to say
35       that the permissions will not change between the test and the real
36       operation?).  Therefore if you are serious about security, just try the
37       real operation and test for its success - think in terms of atomic
38       operations.
39
40       subpragma access
41
42       Currently only one subpragma, "access" is implemented.  It enables (or
43       disables) the use of access() or similar system calls.  This extended
44       filetest functionality is used only when the argument of the operators
45       is a filename, not when it is a filehandle.
46
47
48
49perl v5.8.8                       2001-09-21                     filetest(3pm)
Impressum