Getting the line number and filename is relatively easy: 

sub trace {
  my($package, $filename, $line) = caller;
  # ...
}

[download]

You can also get the subroutine its in. See the docs for caller.

Getting the names of the relevant variables is much harder, because perl does not such a convinent mechanism for compile-time expanded macros as C. However there are things called source filters, and the Filter::Simple module provides a nice interface to them. So, we can use that to make a module that adds a TRACE() macro: 

package TraceMacro;

use Filter::Simple;

FILTER_ONLY 
   code => sub {
s/TRACE\(\s*([^)]+)\s*\)/__PACKAGE__."::_trace(q($1),$1)"/eg; };
# replace each TRACE(...) with <this package>::_trace(q(...),...)

sub _trace {
  my($names,@values) = @_;
  my @names = split /\s*,\s*/, $names; # extract varnames
  my($package,$file,$line) = caller;
  foreach my $i(0..$#names) {
    print STDERR "$file ($line): $names[$i]:'$values[$i]'";
  }
}

[download]

(The module just needs to be saved appropriately to a file called by the name of Package.pm where Package is whatever's specified by the package declaration. (You could change that.))

This has the side-effect of allowing arbitrary expressions instead of just variable names.

update: Usage would be like: 

use TraceMacro;

# ...
TRACE( $foo, $bar );

[download]
If you want to change TRACE to trace (I prefer that compile-time-special things be uppercased), then it shouldn't be hard to fiquire that out.

In reply to Re: Nervously....How do I access the Name of a Perl variable? by wog
in thread Nervously....How do I access the Name of a Perl variable? by Anonymous Monk

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