Beefy Boxes and Bandwidth Generously Provided by pair Networks
more useful options

Why don't word-boundary searches with <CODE>\b</CODE> work for me?

by faq_monk (Initiate)
on Oct 08, 1999 at 00:25 UTC ( #672=perlfaq nodetype: print w/replies, xml ) Need Help??

Current Perl documentation can be found at

Here is our local, out-dated (pre-5.6) version:

Two common misconceptions are that  is a synonym for s+, and that it's the edge between whitespace characters and non-whitespace characters. Neither is correct.  is the place between a w character and a W character (that is,  is the edge of a ``word''). It's a zero-width assertion, just like ^, $, and all the other anchors, so it doesn't consume any characters. the perlre manpage describes the behaviour of all the regexp metacharacters.

Here are examples of the incorrect application of , with fixes:

    "two words" =~ /(w+)(w+)/;          # WRONG
    "two words" =~ /(w+)s+(w+)/;         # right

    " =matchless= text" =~ /=(w+)=/;   # WRONG
    " =matchless= text" =~ /=(w+)=/;       # right

Although they may not do what you thought they did,  and B can still be quite useful. For an example of the correct use of , see the example of matching duplicate words over multiple lines.

An example of using B is the pattern BisB. This will find occurrences of ``is'' on the insides of words only, as in ``thistle'', but not ``this'' or ``island''.

Log In?

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

How do I use this? | Other CB clients
Other Users?
Others browsing the Monastery: (5)
As of 2022-01-23 23:52 GMT
Find Nodes?
    Voting Booth?
    In 2022, my preferred method to securely store passwords is:

    Results (64 votes). Check out past polls.