1PadWalker(3) User Contributed Perl Documentation PadWalker(3)
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6 PadWalker - play with other peoples' lexical variables
7
9 use PadWalker qw(peek_my peek_our peek_sub closed_over);
10 ...
11
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 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 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 peek_my LEVEL
25 peek_our LEVEL
26 The LEVEL argument is interpreted just like the argument to
27 "caller". So peek_my(0) returns a reference to a hash of all the
28 "my" variables that are currently in scope; peek_my(1) returns a
29 reference to a hash of all the "my" variables that are in scope at
30 the point where the current sub was called, and so on.
31 "peek_our" works in the same way, except that it lists the "our"
33 variables rather than the "my" variables.
34 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 For example:
40 my $x = 12;
42 my $h = peek_my (0);
43 ${$h->{'$x'}}++;
44 print $x; # prints 13
46 Or a more complex example:
48 sub increment_my_x {
50 my $h = peek_my (1);
51 ${$h->{'$x'}}++;
52 }
53 my $x=5;
55 increment_my_x;
56 print $x; # prints 6
57 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
61 usually be undefined unless the sub is in use (i.e. in the call-
62 chain) at the time. On the other hand:
63 my $x = "Hello!";
65 my $r = peek_sub(sub {$x})->{'$x'};
66 print "$$r\n"; # prints 'Hello!'
67 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
71 deprecated in a future version in favour of some alternative
72 interface.
73 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 set_closed_over SUB, HASH_REF
82 "set_closed_over" reassigns the pad variables that are closed over
83 by the subroutine.
84 The second argument is a hash of references, much like the one
86 returned from "closed_over".
87 var_name LEVEL, VAR_REF
89 var_name SUB, VAR_REF
90 "var_name(sub, var_ref)" returns the name of the variable referred
91 to by "var_ref", provided it is a "my" variable used in the sub.
92 The "sub" parameter can be either a CODE reference or a number. If
93 it's a number, it's treated the same way as the argument to
94 "peek_my".
95 For example,
97 my $foo;
99 print var_name(0, \$foo); # prints '$foo'
100 sub my_name {
102 return var_name(1, shift);
103 }
104 print my_name(\$foo); # ditto
105
107 Robin Houston <robin@cpan.org>
108 With contributions from Richard Soberberg, Jesse Luehrs and Yuval
110 Kogman, bug-spotting from Peter Scott, Dave Mitchell and Goro Fuji, and
111 suggestions from demerphq.
112
114 Devel::LexAlias, Devel::Caller, Sub::Parameters
115
117 Copyright (c) 2000-2009, Robin Houston. All Rights Reserved. This
118 module is free software. It may be used, redistributed and/or modified
119 under the same terms as Perl itself.
120perl v5.36.0 2022-07-22 PadWalker(3)