Hello monks,

I have been staring at this problem all day, and my error refuses to get up and wave its arms at me.

I'm writing a perl script to munge an XML DTD (for reasons we needn't go into). One of the script's tasks is to find parameter entity definitions that are empty and remove the references to those entities from any element definitions.

# $entity = the name of the entity (already initialized)
# $text = the full DTD (already initialized)

# comment out the empty entity definition
# e.g., <!ENTITY % foo  "    "  >
# so far this section works fine, wrapping the empty entity definition
+ in comment tags
if ( $text =~ /(<!ENTITY\s+%\s+$entity\s+\"\s+\"\s+>)/ ) {

    print "Commenting out empty entity '$entity'\n";
    my $entity_def  = $1;
    $text =~ s/$entity_def/<!--\n$entity_def\n-->/;
}

# here's the problem: I want to find
# <!ELEMENT bar (#PCDATA  %foo;)*  >
# and remove the "%foo;"

if ( $text =~ /(<!ELEMENT\s+(\S+)\s+\(.*?$entity.+?\).+?>)/ ) {

    my $element_def  = $1;
    my $element_name = $2;

    print "Found empty entity '$entity' in $element_name " .
              "content model: $element_def\n";

    my $new_element_def = $element_def;

    $new_element_def =~ s/\|?\s*%$entity;//;

    print "Looking for $element_def\n";

    # this NEVER PRINTS--WHY?
    print "Found it!\n" if $text =~ /$element_def/;
}
[download]

I always manage to capture the element definition in $element_def, but my final regex never works, and I can't figure out why.