[regex] match 2 or more times

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Re: [regex] match 2 or more times by kvale (Monsignor) on Mar 25, 2004 at 23:38 UTC
The regex fails on , e.g., 5 because `(11+){2,}` can match different lengths for different instances: the first match will be of length 3 and the second will be of length 2. By contrast, the first regexp enforces every match to be the same length, thus effectively dividing without a remainder when it matches. -Mark	[reply] [d/l]
Re: Re: [regex] match 2 or more times by Jaap (Curate) on Mar 25, 2004 at 23:58 UTC
Ah! That's it. Thank you for the explanation.	[reply]
Re: [regex] match 2 or more times by davido (Cardinal) on Mar 25, 2004 at 23:31 UTC
YAPE::Regex::Explain can help here: `use strict; use warnings; use YAPE::Regex::Explain; my $REx1 = qr/^(11+)(\1)+$/; my $REx2 = qr/^(11+){2,}$/; my $exp1 = YAPE::Regex::Explain->new($REx1)->explain; my $exp2 = YAPE::Regex::Explain->new($REx2)->explain; print 'm/^(11+)(\1)+$/', "\n", $exp1, "\n"; print 'm/^(11+){2,}$/', "\n", $exp2, "\n";` [download] And the output: m/^(11+)(\1)+$/ The regular expression: (?-imsx:^(11+)(\1)+$) matches as follows: NODE EXPLANATION ---------------------------------------------------------------------- (?-imsx: group, but do not capture (case-sensitive) (with ^ and $ matching normally) (with . not matching \n) (matching whitespace and # normally): ---------------------------------------------------------------------- ^ the beginning of the string ---------------------------------------------------------------------- ( group and capture to \1: ---------------------------------------------------------------------- 1 '1' ---------------------------------------------------------------------- 1+ '1' (1 or more times (matching the most amount possible)) ---------------------------------------------------------------------- ) end of \1 ---------------------------------------------------------------------- ( group and capture to \2 (1 or more times (matching the most amount possible)): ---------------------------------------------------------------------- \1 what was matched by capture \1 ---------------------------------------------------------------------- )+ end of \2 (NOTE: because you're using a quantifier on this capture, only the LAST repetition of the captured pattern will be stored in \2) ---------------------------------------------------------------------- $ before an optional \n, and the end of the string ---------------------------------------------------------------------- ) end of grouping ---------------------------------------------------------------------- m/^(11+){2,}$/ The regular expression: (?-imsx:^(11+){2,}$) matches as follows: NODE EXPLANATION ---------------------------------------------------------------------- (?-imsx: group, but do not capture (case-sensitive) (with ^ and $ matching normally) (with . not matching \n) (matching whitespace and # normally): ---------------------------------------------------------------------- ^ the beginning of the string ---------------------------------------------------------------------- ( group and capture to \1 (at least 2 times (matching the most amount possible)): ---------------------------------------------------------------------- 1 '1' ---------------------------------------------------------------------- 1+ '1' (1 or more times (matching the most amount possible)) ---------------------------------------------------------------------- ){2,} end of \1 (NOTE: because you're using a quantifier on this capture, only the LAST repetition of the captured pattern will be stored in \1) ---------------------------------------------------------------------- $ before an optional \n, and the end of the string ---------------------------------------------------------------------- ) end of grouping ---------------------------------------------------------------------- [download] There are some subtile differences, especially if you're relying on $1 and $2 after the match. Dave	[reply] [d/l] [select]

(11+){2,}

By contrast, the first regexp enforces every match to be the same length, thus effectively dividing without a remainder when it matches.

-Mark

[reply]
[d/l]

Ah! That's it. Thank you for the explanation.

[reply]

YAPE::Regex::Explain

use strict;
use warnings;
use YAPE::Regex::Explain;

my $REx1 = qr/^(11+)(\1)+$/;
my $REx2 = qr/^(11+){2,}$/;
my $exp1 = YAPE::Regex::Explain->new($REx1)->explain;
my $exp2 = YAPE::Regex::Explain->new($REx2)->explain;

print 'm/^(11+)(\1)+$/', "\n", $exp1, "\n";
print 'm/^(11+){2,}$/', "\n", $exp2, "\n";
[download]

And the output:

m/^(11+)(\1)+$/
The regular expression:

(?-imsx:^(11+)(\1)+$)

matches as follows:
  
NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    1                        '1'
----------------------------------------------------------------------
    1+                       '1' (1 or more times (matching the most
                             amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  (                        group and capture to \2 (1 or more times
                           (matching the most amount possible)):
----------------------------------------------------------------------
    \1                       what was matched by capture \1
----------------------------------------------------------------------
  )+                       end of \2 (NOTE: because you're using a
                           quantifier on this capture, only the LAST
                           repetition of the captured pattern will be
                           stored in \2)
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

m/^(11+){2,}$/
The regular expression:

(?-imsx:^(11+){2,}$)

matches as follows:
  
NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  (                        group and capture to \1 (at least 2 times
                           (matching the most amount possible)):
----------------------------------------------------------------------
    1                        '1'
----------------------------------------------------------------------
    1+                       '1' (1 or more times (matching the most
                             amount possible))
----------------------------------------------------------------------
  ){2,}                    end of \1 (NOTE: because you're using a
                           quantifier on this capture, only the LAST
                           repetition of the captured pattern will be
                           stored in \1)
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

There are some subtile differences, especially if you're relying on $1 and $2 after the match.

Dave

[reply]
[d/l]
[select]