Beefy Boxes and Bandwidth Generously Provided by pair Networks
Syntactic Confectionery Delight
 
PerlMonks  

How do I match this without lookbehind?

( #45668=categorized question: print w/ replies, xml ) Need Help??
Contributed by tedv on Dec 08, 2000 at 05:48 UTC
Q&A  > regular expressions


Description:

Suppose I have a string that matches /^(\~?.)*$/ and I want to split it into each atomic piece that would be matched by (\~?.). How would I code such a regular expression for split? I'd like to use lookbehind, crafting an expression that says, "Split after every non-tilde character", but my O'Reilly Regular Expression book says that perl doesn't support lookbehind. Any suggestions?

-Ted

Answer: How do I match this without lookbehind?
contributed by Adam

my @results = grep {$_} split /([~]*?[^~])/, $input;
Answer: How do I match this without lookbehind?
contributed by chipmunk

When the Regular Expressions book was published, the latest version of Perl was 5.005_03. As of 5.6.0, Perl does support lookbehind.

However, you really don't need lookbehind or split to solve this problem: @matches = $string =~ /~?./g;

Answer: How do I match this without lookbehind?
contributed by runrig

Sometimes split is not the best answer for splitting:

my @results; push @results, $1 while /(~?.)/g;
Answer: How do I match this without lookbehind?
contributed by Shakya

my @results = $string =~ m!([^~]+)!g;
Answer: How do I match this without lookbehind?
contributed by I0

Perl v5.6.0 does suport lookbehind

split /(?<=[^~])/ #or split /(?<!~)/ #or /(~?.)/g

Please (register and) log in if you wish to add an answer



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • Outside of code tags, you may need to use entities for some characters:
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others scrutinizing the Monastery: (3)
    As of 2014-09-17 03:59 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      How do you remember the number of days in each month?











      Results (57 votes), past polls