FAQ 6.13 What does it mean that regexes are greedy? How can I get around it?

Discussion in 'Perl Misc' started by PerlFAQ Server, Apr 18, 2011.

  1. This is an excerpt from the latest version perlfaq6.pod, which
    comes with the standard Perl distribution. These postings aim to
    reduce the number of repeated questions as well as allow the community
    to review and update the answers. The latest version of the complete
    perlfaq is at http://faq.perl.org .

    --------------------------------------------------------------------

    6.13: What does it mean that regexes are greedy? How can I get around it?

    Most people mean that greedy regexes match as much as they can.
    Technically speaking, it's actually the quantifiers ("?", "*", "+",
    "{}") that are greedy rather than the whole pattern; Perl prefers local
    greed and immediate gratification to overall greed. To get non-greedy
    versions of the same quantifiers, use ("??", "*?", "+?", "{}?").

    An example:

    $s1 = $s2 = "I am very very cold";
    $s1 =~ s/ve.*y //; # I am cold
    $s2 =~ s/ve.*?y //; # I am very cold

    Notice how the second substitution stopped matching as soon as it
    encountered "y ". The "*?" quantifier effectively tells the regular
    expression engine to find a match as quickly as possible and pass
    control on to whatever is next in line, like you would if you were
    playing hot potato.



    --------------------------------------------------------------------

    The perlfaq-workers, a group of volunteers, maintain the perlfaq. They
    are not necessarily experts in every domain where Perl might show up,
    so please include as much information as possible and relevant in any
    corrections. The perlfaq-workers also don't have access to every
    operating system or platform, so please include relevant details for
    corrections to examples that do not work on particular platforms.
    Working code is greatly appreciated.

    If you'd like to help maintain the perlfaq, see the details in
    perlfaq.pod.
    PerlFAQ Server, Apr 18, 2011
    #1
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Dan Kelly

    Greedy and non greedy quantifiers

    Dan Kelly, Jan 17, 2008, in forum: Ruby
    Replies:
    4
    Views:
    142
    Robert Klemme
    Jan 19, 2008
  2. John Livermore

    how to get around greedy * operator?

    John Livermore, Sep 7, 2004, in forum: Javascript
    Replies:
    1
    Views:
    67
    Lasse Reichstein Nielsen
    Sep 7, 2004
  3. Matt Garrish

    greedy v. non-greedy matching

    Matt Garrish, Feb 16, 2004, in forum: Perl Misc
    Replies:
    4
    Views:
    161
    Matt Garrish
    Feb 16, 2004
  4. PerlFAQ Server
    Replies:
    0
    Views:
    167
    PerlFAQ Server
    Jan 14, 2011
  5. PerlFAQ Server
    Replies:
    0
    Views:
    119
    PerlFAQ Server
    Feb 14, 2011
Loading...

Share This Page