In Perl, how can I check from which module a given function was imported?

Question

I have a code which calls the function. But I don't know the module this function belongs to. I need it to modify this function.

How can I check it?

Answer 1

The Devel::Peek module is very handy to get all sorts of information about variables. One of the things you can do with it is dump a reference to a subroutine and get the name of the glob it came from:

$  perl -MDevel::Peek -MList::Util=first -e'Dump(\&first)'
SV = IV(0x1094e20) at 0x1094e28
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x11183b0
  SV = PVCV(0x10ff1f0) at 0x11183b0
    REFCNT = 3
    FLAGS = (POK,pPOK)
    PROTOTYPE = "&@"
    COMP_STASH = 0x0
    XSUB = 0x7f7ecbdc61b0
    XSUBANY = 0
    GVGV::GV = 0x11183c8        "List::Util" :: "first"
    FILE = "ListUtil.c"
    DEPTH = 0
    FLAGS = 0x800
    OUTSIDE_SEQ = 0
    PADLIST = 0x0
    OUTSIDE = 0x0 (null)

the GVGV::GV part in there is the important bit.

An alternative solution would be Sub::Identify, which really only gives you names for code references you hand to it. However, knowing about Devel::Peek is handy in many other situations too, so I mentioned that first.

Answer 2

Perl's debugger can dig down the way you want. For example:

main::(-e:1):  0
  DB<1> sub foo {}

  DB<2> x \&foo
0  CODE(0xca6898)
   -> &main::foo in (eval 5)[/usr/share/perl/5.10/perl5db.pl:638]:2-2

It does this using Devel::Peek:

=head2 C<CvGV_name_or_bust> I<coderef>

Calls L<Devel::Peek> to try to find the glob the ref lives in; returns
C<undef> if L<Devel::Peek> can't be loaded, or if C<Devel::Peek::CvGV> can't
find a glob for this ref.

Returns C<< I<package>::I<glob name> >> if the code ref is found in a glob.

=cut

sub CvGV_name_or_bust {
    my $in = shift;
    return unless ref $in;
    $in = \&$in;            # Hard reference...
    eval { require Devel::Peek; 1 } or return;
    my $gv = Devel::Peek::CvGV($in) or return;
    *$gv{PACKAGE} . '::' . *$gv{NAME};
} ## end sub CvGV_name_or_bust

You might exercise it with

#! /usr/bin/perl

use warnings;
use strict;

package Foo;

sub bar {}

package main;

BEGIN { *baz = \&Foo::bar }

sub CvGV_name_or_bust { ... }

print CvGV_name_or_bust(\&baz), "\n";

Output:

Foo::bar

Note that the example above gives Foo:bar a different name, but you get both the package where the aliased sub resides and also its name there.

Answer 3

If the function was automatically imported from another module using Exporter, it can be found in this module's @EXPORT global variable:

perl -MEncode -e 'print join "\n", @Encode::EXPORT'
decode   
decode_utf8
...   

You can provide a list of functions to use. This way you will always know which package a function belongs:

use Encode       qw[ encode ]; # encode() imported from the Encode module
use Data::Dumper qw[];         # no functions imported from Data::Dumper