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5ff3f7a4 GS |
1 | package filetest; |
2 | ||
3 | =head1 NAME | |
4 | ||
5 | filetest - Perl pragma to control the filetest permission operators | |
6 | ||
7 | =head1 SYNOPSIS | |
8 | ||
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 | ||
16 | =head1 DESCRIPTION | |
17 | ||
18 | This pragma tells the compiler to change the behaviour of the filetest | |
80d06f2d JH |
19 | permissions operators, the C<-r> C<-w> C<-x> C<-R> C<-W> C<-X> |
20 | (see L<perlfunc>). | |
5ff3f7a4 GS |
21 | |
22 | The default behaviour to use the mode bits as returned by the stat() | |
23 | family of calls. This, however, may not be the right thing to do if | |
24 | for example various ACL (access control lists) schemes are in use. | |
25 | For such environments, C<use filetest> may help the permission | |
26 | operators to return results more consistent with other tools. | |
27 | ||
28 | Each "use filetest" or "no filetest" affects statements to the end of | |
29 | the enclosing block. | |
30 | ||
31 | There may be a slight performance decrease in the filetests | |
32 | when C<use filetest> is in effect, because in some systems | |
33 | the extended functionality needs to be emulated. | |
34 | ||
05e53ac4 | 35 | B<NOTE>: using the file tests for security purposes is a lost cause |
80d06f2d JH |
36 | from the start: there is a window open for race conditions (who is to |
37 | say that the permissions will not change between the test and the real | |
38 | operation?). Therefore if you are serious about security, just try | |
39 | the real operation and test for its success. Think atomicity. | |
5ff3f7a4 GS |
40 | |
41 | =head2 subpragma access | |
42 | ||
43 | Currently only one subpragma, C<access> is implemented. It enables | |
44 | (or disables) the use of access() or similar system calls. This | |
45 | extended filetest functionality is used only when the argument of the | |
46 | operators is a filename, not when it is a filehandle. | |
47 | ||
48 | =cut | |
49 | ||
50 | sub import { | |
51 | if ( $_[1] eq 'access' ) { | |
52 | $^H |= 0x00400000; | |
53 | } else { | |
54 | die "filetest: the only implemented subpragma is 'access'.\n"; | |
55 | } | |
56 | } | |
57 | ||
58 | sub unimport { | |
59 | if ( $_[1] eq 'access' ) { | |
60 | $^H &= ~0x00400000; | |
61 | } else { | |
62 | die "filetest: the only implemented subpragma is 'access'.\n"; | |
63 | } | |
64 | } | |
65 | ||
66 | 1; |