How to catch roman numbers inside string?

Question

I want to catch roman numbers inside string (numbers below 80 is fine enough). I found good base for it in How do you match only valid roman numerals with a regular expression?. Problem is: it deals with whole strings. I did not found yet a solution how to detect roman numbers inside string, because there is nothing mandatory, every group may be optional. So far i tried something like this:

my $x = ' some text I-LXIII iv more ';

if (  $x =~  s/\b(
                    (
                        (XC|XL|L?X{0,3}) # first group 10-90
                    |
                        (IX|IV|V?I{0,3}) # second group 1-9
                    )+
            )
        \b/>$1</xgi ) { # mark every occurrence
    say $x;
}

__END__
 ><some>< ><text>< ><>I<><-><>LXIII<>< ><>iv<>< ><more>< 
 desired output:
  some text >I<->LXIII< >iv< more 

So, this one captures word boundaries by themself too, because all groups are optional. How to get it done? How to make one of those 2 groups mandatory while there is no possible to tell which one is mandatory? Other approaches to catch romans are welcome too.

Answer 1

You can use Roman CPAN module

use Roman;

my $x = ' some text I-LXIII VII XCVI IIIXII iv more ';
if (  $x =~  
    s/\b
    (
        [IVXLC]+
    )
    \b
    /isroman($1) ? ">$1<" : $1/exgi ) {
    say $x;
}

output:

some text >I<->LXIII< >VII< >XCVI< IIIXII >iv< more 

Answer 2

This is where Perl lets us down with its missing \< and \> (beginning and end word boundary) constructs that are available elsewhere. A pattern like \b...\b will match even if the ... consumes none of the target string because the second \b will happily match the beginning word boundary a second time.

However an end word boundary is just (?<=\w)(?!\w) so we can use this instead.

This program will do what you want. It does a look-ahead for a string of potential Roman characters enclosed in word boundaries (so we must be at a beginning word boundary) and then checks for a legal Roman number that isn't followed by a word character (so now we're at an end word boundary).

Note that I've reversed your >...< marks as they were confusing me.

use strict;
use warnings;

use feature 'say';

my $x = ' some text I-LXIII iv more ';

if ( $x =~ s{
    (?= \b [CLXVI]+ \b )
    (
      (?:XC|XL|L?X{0,3})?
      (?:IX|IV|V?I{0,3})?
    )
    (?!\w)
    }
    {<$1>}xgi ) {

    say $x;
}

output

some text <I>-<LXIII> <iv> more