Re: Question about perlreref - are {n} and {n}? different?

Dr.Ruud wrote: 
usenet@xxxxxxxxxxxxxxx schreef:

perlreref::QUANTIFIERS says:

Quantifiers are greedy by default -- match the longest leftmost.
Maximal Minimal Allowed range
------- ------- -------------
{n,m}   {n,m}?  Must occur at least n times but no more than m times

The 'Must occur ... no more than m times' is not accurate. 

It is accurate, when you realize that it is talking about the
characters that were actually part of the matched string.
Characters outside the matched string are irrelevant when
the match succeeds.

#!/usr/bin/perl -w
use strict;

  my $s = 'a'x100; # is more than 50 times

  sub run {
    local ($,, $\) = (' ', "\n");
    my $re; ($re, $_) = @_;
    s/$re/$1/;
    print length, length($1);
  }

  run 'a{10,50}?(.*)'  , $s;
  run 'a{10,50}?(.*?)a', $s;
  run 'a{10,50}?(.*?)' , $s;
  run 'a{10,50}(.*?)'  , $s;
  run 'a{10,50}(.*)'   , $s;

output:
90 90
89 0
90 0
50 0
50 50


run 'a{10,50}?(.*)'  , $s;
  First part matches minimum; 'a'x10.
  Second part matches rest of string; 'a'x90.
  Replacing first+second with just second = 'a'x90.
  Expected result of "90 90" = yes.

run 'a{10,50}?(.*?)a', $s;
  First part matches minimum; 'a'x10.
  Second part matches the null string.
  Third part matches 11th a.
  Replacing first+second+third with just second leaves the
  89 characters that were not part of the overall match = 'a'x89.
  Expected result of "89 0" = yes.

run 'a{10,50}?(.*?)' , $s;
  First part matches minimum; 'a'x10.
  Second part matches the null string.
  Replacing first+second with just second leaves the
  90 characters that were not part of the overall match = 'a'x90.
  Expected result of "90 0" = yes.

run 'a{10,50}(.*?)'  , $s;
  First part matches maximum; 'a'x50.
  Second part matches the null string.
  Replacing first+second with just second leaves the
  50 characters that were not part of the overall match = 'a'x50.
  Expected result of "50 0" = yes.

run 'a{10,50}(.*)'   , $s;
  First part matches maximum; 'a'x50.
  Second part matches rest of string; 'a'x50.
  Replacing first+second with just second = 'a'x50.
  Expected result of "50 50" = yes.

The s/$re/$1/ just confuses things.  This is better:

#!/usr/bin/perl -w
use strict;

  my $s = 'a'x100; # is more than 50 times

  sub run {
    my $re; ($re, $_) = @_;
    /$re/;
    print "\$1='$1' \$2='$2' rest=|$'|\n";
  }

run '(a{10,50}?)(.*)' , $s;
run '(a{10,50}?)(.*?)a', $s;
run '(a{10,50}?)(.*?)' , $s;
run '(a{10,50})(.*?)' , $s;
run '(a{10,50})(.*)' , $s;
$1='aaaaaaaaaa' $2='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa' rest=||
$1='aaaaaaaaaa' $2='' rest=|aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
$1='aaaaaaaaaa' $2='' rest=|aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
$1='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa' $2='' rest=|aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa|
$1='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa' $2='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa' rest=||

This shows that /a{10,50}?/ matches the first 10 characters of the
string and /a{10,50}/ matches the first 50 characters of the string.

	-Joe
.

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