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920dae64 AT |
1 | package filetest; |
2 | ||
3 | our $VERSION = '1.01'; | |
4 | ||
5 | =head1 NAME | |
6 | ||
7 | filetest - Perl pragma to control the filetest permission operators | |
8 | ||
9 | =head1 SYNOPSIS | |
10 | ||
11 | $can_perhaps_read = -r "file"; # use the mode bits | |
12 | { | |
13 | use filetest 'access'; # intuit harder | |
14 | $can_really_read = -r "file"; | |
15 | } | |
16 | $can_perhaps_read = -r "file"; # use the mode bits again | |
17 | ||
18 | =head1 DESCRIPTION | |
19 | ||
20 | This pragma tells the compiler to change the behaviour of the filetest | |
21 | permission operators, C<-r> C<-w> C<-x> C<-R> C<-W> C<-X> | |
22 | (see L<perlfunc>). | |
23 | ||
24 | The default behaviour is to use the mode bits as returned by the stat() | |
25 | family of calls. This, however, may not be the right thing to do if | |
26 | for example various ACL (access control lists) schemes are in use. | |
27 | For such environments, C<use filetest> may help the permission | |
28 | operators to return results more consistent with other tools. | |
29 | ||
30 | Each "use filetest" or "no filetest" affects statements to the end of | |
31 | the enclosing block. | |
32 | ||
33 | There may be a slight performance decrease in the filetests | |
34 | when C<use filetest> is in effect, because in some systems | |
35 | the extended functionality needs to be emulated. | |
36 | ||
37 | B<NOTE>: using the file tests for security purposes is a lost cause | |
38 | from the start: there is a window open for race conditions (who is to | |
39 | say that the permissions will not change between the test and the real | |
40 | operation?). Therefore if you are serious about security, just try | |
41 | the real operation and test for its success - think in terms of atomic | |
42 | operations. | |
43 | ||
44 | =head2 subpragma access | |
45 | ||
46 | Currently only one subpragma, C<access> is implemented. It enables | |
47 | (or disables) the use of access() or similar system calls. This | |
48 | extended filetest functionality is used only when the argument of the | |
49 | operators is a filename, not when it is a filehandle. | |
50 | ||
51 | =cut | |
52 | ||
53 | $filetest::hint_bits = 0x00400000; # HINT_FILETEST_ACCESS | |
54 | ||
55 | sub import { | |
56 | if ( $_[1] eq 'access' ) { | |
57 | $^H |= $filetest::hint_bits; | |
58 | } else { | |
59 | die "filetest: the only implemented subpragma is 'access'.\n"; | |
60 | } | |
61 | } | |
62 | ||
63 | sub unimport { | |
64 | if ( $_[1] eq 'access' ) { | |
65 | $^H &= ~$filetest::hint_bits; | |
66 | } else { | |
67 | die "filetest: the only implemented subpragma is 'access'.\n"; | |
68 | } | |
69 | } | |
70 | ||
71 | 1; |