1PadWalker(3)          User Contributed Perl Documentation         PadWalker(3)
2
3
4

NAME

6       PadWalker - play with other peoples' lexical variables
7

SYNOPSIS

9         use PadWalker qw(peek_my peek_our peek_sub closed_over);
10         ...
11

DESCRIPTION

13       PadWalker is a module which allows you to inspect (and even change!)
14       lexical variables in any subroutine which called you. It will only show
15       those variables which are in scope at the point of the call.
16
17       PadWalker is particularly useful for debugging. It's even used by
18       Perl's built-in debugger. (It can also be used for evil, of course.)
19
20       I wouldn't recommend using PadWalker directly in production code, but
21       it's your call. Some of the modules that use PadWalker internally are
22       certainly safe for and useful in production.
23
24       peek_my LEVEL
25       peek_our LEVEL
26           The LEVEL argument is interpreted just like the argument to "call‐
27           er".  So peek_my(0) returns a reference to a hash of all the "my"
28           variables that are currently in scope; peek_my(1) returns a refer‐
29           ence to a hash of all the "my" variables that are in scope at the
30           point where the current sub was called, and so on.
31
32           "peek_our" works in the same way, except that it lists the "our"
33           variables rather than the "my" variables.
34
35           The hash associates each variable name with a reference to its
36           value. The variable names include the sigil, so the variable $x is
37           represented by the string '$x'.
38
39           For example:
40
41             my $x = 12;
42             my $h = peek_my (0);
43             ${$h->{'$x'}}++;
44
45             print $x;  # prints 13
46
47           Or a more complex example:
48
49             sub increment_my_x {
50               my $h = peek_my (1);
51               ${$h->{'$x'}}++;
52             }
53
54             my $x=5;
55             increment_my_x;
56             print $x;  # prints 6
57
58       peek_sub SUB
59           The "peek_sub" routine takes a coderef as its argument, and returns
60           a hash of the "my" variables used in that sub. The values will usu‐
61           ally be undefined unless the sub is in use (i.e. in the call-chain)
62           at the time. On the other hand:
63
64             my $x = "Hello!";
65             my $r = peek_sub(sub {$x})->{'$x'};
66             print "$$r\n";        # prints 'Hello!'
67
68           If the sub defines several "my" variables with the same name,
69           you'll get the last one. I don't know of any use for "peek_sub"
70           that isn't broken as a result of this, and it will probably be dep‐
71           recated in a future version in favour of some alternative inter‐
72           face.
73
74       closed_over SUB
75           "closed_over" is similar to "peek_sub", except that it only lists
76           the "my" variables which are used in the subroutine but defined
77           outside: in other words, the variables which it closes over. This
78           does have reasonable uses: see Data::Dump::Streamer, for example (a
79           future version of which may in fact use "closed_over").
80
81       var_name LEVEL, VAR_REF
82       var_name SUB,   VAR_REF
83           "var_name(sub, var_ref)" returns the name of the variable referred
84           to by "var_ref", provided it is a "my" variable used in the sub.
85           The "sub" parameter can be either a CODE reference or a number. If
86           it's a number, it's treated the same way as the argument to
87           "peek_my".
88
89           For example,
90
91             my $foo;
92             print var_name(0, \$foo);    # prints '$foo'
93
94             sub my_name {
95               return var_name(1, shift);
96             }
97             print my_name(\$foo);        # ditto
98

AUTHOR

100       Robin Houston <robin@cpan.org>
101
102       With contributions from Richard Soberberg, bug-spotting from Peter
103       Scott and Dave Mitchell, and suggestions from demerphq.
104

SEE ALSO

106       Devel::LexAlias, Devel::Caller, Sub::Parameters
107

109       Copyright (c) 2000-2007, Robin Houston. All Rights Reserved.  This mod‐
110       ule is free software. It may be used, redistributed and/or modified
111       under the same terms as Perl itself.
112
113
114
115perl v5.8.8                       2007-01-05                      PadWalker(3)
Impressum