Passing regexp as argument

loris has asked for the wisdom of the Perl Monks concerning the following question:

Hello wiser ones,

How would I pass a regexp as a parameter to a subroutine? I would like to do something like:

changeName($topNodeOfXmlTree,'s/WrongNode/RightNode/');

and have the function recurse through the XML tree and change, in my case, the node names:

sub changeNodeNames {
  my ($self,$node,$regEx) = @_;

  my $nodeName = $node->nodeName;
  $nodeName =~ $regEx;
  ...
[download]

The above, however, does not work.

Thanks for your help,

loris

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Re: Passing regexp as argument by Zaxo (Archbishop) on Dec 20, 2004 at 10:10 UTC
You are trying to pass a whole substitution expression, not just a regex. You need eval STRING to do what you want, `eval "\$nodeName =~ $regEx";` Note the escaped sigil in $nodeName. That is to prevent the variable from having its value interpolated before evaluation. I'd be inclined to pass the regex and substitution as two arguments and interpolate them `sub changeNodeNames { my ($self,$node,$regEx,$subst) = @_; my $nodeName = $node->nodeName; $nodeName =~ s/$regEx/$subst/; # . . . } $foo->changeNodeNames($anode, qr/foo/, 'bar');` [download] After Compline, Zaxo	[reply] [d/l] [select]
Re: Passing regexp as argument by edan (Curate) on Dec 20, 2004 at 09:56 UTC
Pass string and the replacement as 2 arguments: `$obj->changeName($topNodeOfXmlTree, 'WrongNode', 'RightNode'); sub changeNodeNames { my ($self,$node,$from,$to) = @_; my $nodeName = $node->nodeName; $nodeName =~ s/$from/$to/; ... }` [download] -- edan	[reply] [d/l]
Re: Passing regexp as argument by BUU (Prior) on Dec 20, 2004 at 16:34 UTC
The others before me have answered the exact question you asked, namely how you pass a regex, but if you want a slightly more flexible solution (and better than a string eval), you should consider passing a subreference, which you then call to modify node name. For your code above would look like: `sub change_node_names { my ($self, $node, $code) = @_; $nodeName = $code->( $nodeName ) } $foo->change_node_names( $node, sub { my $name = shift; $name =~ s/wrongnode/rightnode/; return $name } );` [download] While this requires slightly more effort to call the subroutine, it is much more flexible as you can put literally any perl code inside of the annonymous sub, which is what the funnny `sub { }` creates.	[reply] [d/l] [select]