Perl 5 - longest token matching in regexp (using alternation) - regex

Question

Is possible to force a Perl 5 regexp match longest possible string, if the regexp is, for example:
a|aa|aaa
I found is probably default in perl 6, but in perl 5, how i can get this behavior?
EXAMPLE pattern:
[0-9]|[0-9][0-9]|[0-9][0-9][0-9][0-9]
If I have string 2.10.2014, then first match will be 2, which is ok; but the next match will be 1, and this is not ok because it should be 10. Then 2014 will be 4 subsequently matches 2,0,1,4, but it should be 2014 using [0-9][0-9][0-9][0-9]. I know I could use [0-9]+, but I can't.

Answer 1

General solution: Put the longest one first.
my ($longest) = /(aaa|aa|a)/
Specific solution: Use
my ($longest) = /([0-9]{4}|[0-9]{1,2})/
If you can't edit the pattern, you'll have to find every possibility and find the longest of them.
my $longest;
while (/([0-9]|[0-9][0-9]|[0-9][0-9][0-9][0-9])/g) {
$longest = $1 if length($1) > length($longest);
}

Answer 2

The sanest solution I can see for unknown patterns is to match every possible pattern, look at the length of the matched substrings and select the longest substring:
my #patterns = (qr/a/, qr/a(a)/, qr/b/, qr/aaa/);
my $string = "aaa";
my #substrings = map {$string =~ /($_)/; $1 // ()} #patterns;
say "Matched these substrings:";
say for #substrings;
my $longest_token = (sort { length $b <=> length $a } #substrings)[0];
say "Longest token was: $longest_token";
Output:
Matched these substrings:
a
aa
aaa
Longest token was: aaa
For known patterns, one would sort them manually so that first-match is the same as longest-match:
"aaa" =~ /(aaa|aa|b|a)/;
say "I know that this was the longest substring: $1";

Answer 3

The alternation will use the first alternative that matches, so just write /aaa|aa|a/ instead.
For the example you have shown in your question, just put the longest alternative first like I said:
[0-9][0-9][0-9][0-9]|[0-9][0-9]|[0-9]

Answer 4

perl -Mstrict -Mre=/xp -MData::Dumper -wE'
{package Data::Dumper;our($Indent,$Sortkeys,$Terse,$Useqq)=(1)x4}
sub _dump { Dumper(shift) =~ s{(\[.*?\])}{$1=~s/\s+/ /gr}srge }
my ($count, %RS);
my $s= "aaaabbaaaaabbab";
$s =~ m{ \G a+b? (?{ $RS{ $+[0] - $-[0] } //= [ ${^MATCH}, $-[0] ]; $count++ }) (*FAIL) };
say sprintf "RS: %s", _dump(\%RS);
say sprintf "count: %s", $count;
'
RS: {
"1" => [ "a", 0 ],
"2" => [ "aa", 0 ],
"3" => [ "aaa", 0 ],
"4" => [ "aaaa", 0 ],
"5" => [ "aaaab", 0 ]
}
count: 5