• What is "if (/.../g)" suppose to mean, "check if it matches, then search the rest of the string to see if it matches too"? It makes no sense, and it will also cause hard to debug errors. Get rid of that "g".

• "(" and ")" have special meaning in regex patterns. If you want to match a string literally, you'll need to convert the string you want to the match into a pattern that matches that string. quotemeta does that.

  my $tr_pat = quotemeta($tr);
  if ($str =~ /$tr_pat/) {
  [download]

  or

  if ($str =~ /\Q$tr\E/) {
  [download]

  or

  if ($str =~ /\Q$tr) {
  [download]

The opening parenthesis "(" is special in regular expressions. See perlre. Most likely you want to use quotemeta before interpolating a string into a regular expression, or use \Q...\E like this:

if ($str =~ m/\Q$tr\E/) {
...
};
[download]

For stylistic points, the /g on your regular expression serves no purpose.

To help us help you better, please do not vaguely rephrase Perl error messages but copy and paste the error messages.

It's not just a stylistic problem.

>perl -E"$x='a'; for (1..2) { if ($x =~ /a/g) { say 1 } else { say 0 }
+ }"
1
0
[download]

And now some issues:

1. You need to quotemeta since your match string contains regular expression Metacharacters ('(' and ')'). You could also manually escape the characters, but you are more likely to run into trouble with that.

2. You shouldn't use g on a regular expression (or any Modifiers) unless you need it. In this case, it is a bug but not the bug you were hitting.

3. And in any case, your string does not contain the term you are searching for. The closest occurrence is <Tr><Tc>At transplantation (POD ), without the '0'.

There are cases where, although the node title doesn't say anything useful, you still can't complain because the OP also couldn't have invented a better title. This is one of those cases.

Examine. The body of the post is good: it contains a code example reduced to minimal and explains what the OP expects it to do and how it fails. The minimal code example doesn't use any advanced features: it doesn't include modules (except for strict) or anything. Until you know the answer, there's no better way to describe the question than "I wrote something very simple in perl and it doesn't work".

Thanks to tye for explaining this phenomenon to me.

I should have, with my chiding, included positive reinforcement for the well-formatted and well-considered body of the post. I certainly agree with that point and will try to remember in the future.

My issue is not with the null-statement title, but with the tone. Whenever I see an exclamation point in a title, let alone three, I interpret it the Perl sense - ! (Please help me). Had the title been "This is Strange - Please help me..", I would not have included the gripe (or better yet, simply "This is Strange"). I should have made this point more clearly - if an old-hand such as yourself misinterpreted my intent, then a new member would undoubtedly have done the same.