How can I get a call stack listing in Perl?

Question

Is there a way I can access (for printout) a list of sub + module to arbitrary depth of sub-calls preceding a current position in a Perl script?

I need to make changes to some Perl modules (.pm's). The workflow is initiated from a web-page thru a cgi-script, passing input through several modules/objects ending in the module where I need to use the data. Somewhere along the line the data got changed and I need to find out where.

Answer 1

You can use Devel::StackTrace.

use Devel::StackTrace;
my $trace = Devel::StackTrace->new;
print $trace->as_string; # like carp

It behaves like Carp's trace, but you can get more control over the frames.

The one problem is that references are stringified and if a referenced value changes, you won't see it. However, you could whip up some stuff with PadWalker to print out the full data (it would be huge, though).

Answer 2

caller can do that, though you may want even more information than that.

Answer 3

While this does not answer your question it might help you solve your problem :-)

Here is an interesting article describing one way how to figure out who changes your variables from Mark Dominus

Answer 4

There's also Carp::confess and Carp::cluck.

Answer 5

Carp::longmess will do what you want, and it's standard.

use Carp qw<longmess>;
use Data::Dumper;
sub A { &B; }
sub B { &C; }
sub C { &D; }
sub D { &E; }

sub E { 
    # Uncomment below if you want to see the place in E
    # local $Carp::CarpLevel = -1; 
    my $mess = longmess();
    print Dumper( $mess );
}

A();
__END__
$VAR1 = ' at - line 14
    main::D called at - line 12
    main::C called at - line 10
    main::B called at - line 8
    main::A() called at - line 23
';

I came up with this sub (Now with optional blessin' action!)

my $stack_frame_re = qr{
    ^                # Beginning of line
    \s*              # Any number of spaces
    ( [\w:]+ )       # Package + sub
    (?: [(] ( .*? ) [)] )? # Anything between two parens
    \s+              # At least one space
    called [ ] at    # "called" followed by a single space
    \s+ ( \S+ ) \s+  # Spaces surrounding at least one non-space character
    line [ ] (\d+)   # line designation
}x;

sub get_stack {
    my @lines = split /\s*\n\s*/, longmess;
    shift @lines;
    my @frames
        = map { 
              my ( $sub_name, $arg_str, $file, $line ) = /$stack_frame_re/;
              my $ref =  { sub_name => $sub_name
                         , args     => [ map { s/^'//; s/'$//; $_ } 
                                         split /\s*,\s*/, $arg_str 
                                       ]
                         , file     => $file
                         , line     => $line 
                         };
              bless $ref, $_[0] if @_;
              $ref
          } 
          @lines
       ;
    return wantarray ? @frames : \@frames;
}