Re: Finding the right $<*digit*> capture variable

I'm not sure where you're going with this either, $#- probably does what you're looking for.

You could also write a subroutine to check which $<DIGIT> values are defined, and return the last one found:

sub last_match {

    # Accepts no args
    # Returns the digit of the last parenthesis match or undef if ther
+e isn't one

    my $match_num = 1;

    if(defined($$match_num)) {    
        while(defined($$match_num)) { $match_num++; }
        $match_num--;
    } 
    else { undef $match_num; }

    return $match_num;
}
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Re: Re: Finding the right $<digit> capture variable by hv (Prior) on Apr 17, 2003 at 13:26 UTC
Beware that this approach cannot discover the last defined match variable, since there may be gaps in the list: for example after `"b" =~ /(a)?(b)/`, `$1` will not be defined even though `$2` is. Since there is no useful absolute limit on the highest numbered match variable you might need to check for, I wondered whether walking the symbol table might give a clue, but no such luck - the symbol table entries for `*1` etc are created only if they are explicitly referenced in the code: `"abcde" =~ /(.)(.)(.)(.)(.)/; my $var = $4; print join ', ', grep !/\D/, keys %::;` [download] prints "`0, 4`". Accordingly, I think it is not possible in pure perl to discover the highest numbered defined match variable using any perl before v5.6.0 (when `@+` and friends were first introduced). Hugo	[reply] [d/l] [select]
Re: Re: Re: Finding the right $<digit> capture variable by diotalevi (Canon) on Apr 17, 2003 at 13:48 UTC
I was thinking of taking the sideways route - instrument the ')' part of a '(...)' group so that the contents of @+ is copied elsewhere for safekeeping. Any time that I'm interested in knowing which newly closed group was just passed I'd look for the index of the newly defined value in @+. So after `(a)?` `$+[1]` and `$+[2]` are undefined. After `(b)` `$+[1]` is still undefined but `$+[2]` is defined (and equal to 2). So... if I can know which @+ entry was just created is that sufficient or will that break as well?	[reply] [d/l] [select]
Re^4: Finding the right $<digit> capture variable by hv (Prior) on Apr 17, 2003 at 14:29 UTC
I think you can combine the information from `@-`, `@+` and `$^N` to get most of the way there: `sub last_closed { my $last = $+[0]; my $len = length $^N; for (1 .. $#+) { return $_ if defined($+[$_]) && $+[$_] == $last && $+[$_] == $len + $-[$_]; } return undef; } "ad" =~ m{ ( (a) (?{ print last_closed() }) (b)? (?{ print last_closed() }) (c?) (?{ print last_closed() }) d ) (?{ print last_closed() }) }x;` [download] This assumes a capture has just been closed; if that isn't necessarily the case, `$last` should instead be calculated as `max(@+[1 .. $#+])`. Obviously this cannot report optional captures that did not capture; also, it can't tell the order of closing of empty strings - `"c" =~ /((a)b)/` vs `"c" =~ /(a)(b)/` - but if you are only interested in non-empty captures, I think this code will give the unique answer. Hugo	[reply] [d/l] [select]