Hello Eily, you wrote:

... if you have $ref = \SOMETHING where SOMETHING comes from a regex ..., running another match may change the value your reference points to.

Whow, I am impressed. Your guess is absolutely right. In fact the input to the method is coming from another regular expression. This is how I call my method:

$l_Value =~ s/([a-zA-Z]\w+)/${$o_Object->GetValue(\ $1)}/gs;
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The regular expression searches for specific placeholders in a string, and tries to replace them with values returned by the method "GetValue".

sub GetValue {
  my $o_Object    = shift;
  my $l_Name_ref  = shift;
  my $l_Value     = undef;

  if (defined($$l_Name_ref)) {
  print STDERR "1 $$l_Name_ref\n" if (defined($$l_Name_ref));
  print STDERR "2 $l_Name_ref\n";
  if ($$l_Name_ref =~ /^[a-zA-Z]\w+$/) {
    print STDERR "3 $l_Name_ref\n";
    print STDERR "4 $$l_Name_ref\n";
    ...
  } else {
    ...
  }
  return \ $l_Value;
}
[download]

So running a regular expression on a reference, which point to a result of another regular expression should be avoided. The solution is to create a copy of the same data before running the next regular expression. Thank you for pointing this out.