#!/usr/bin/perl
use strict;
use warnings;
my $s = "sad day
Good day
May be Bad Day
";
$s =~ s/\w+ \w+/_/gm;
print $s;
I am trying to substitute all spaces between words with _, but it is not working. What is wrong with that?
views:
105answers:
3
+3
A:
This pattern replacement is probably the most efficient solution:
$a =~ s/\b \b/_/g;
amphetamachine
2010-06-02 12:33:09
agreed, it looks good ;--)
mirod
2010-06-02 12:35:51
Please don't use `$a` or `$b` in examples unless it involves [sorting](http://perldoc.perl.org/perlvar.html).
Zaid
2010-06-02 13:45:54
@Zaid - Good point, but I was just using the same variables as the OP.
amphetamachine
2010-06-05 18:12:16
+5
A:
The substitution replaces an entire word (\w+) then a space then an other word by an underscore.
There is really no need to replace (or capture for what matters) those words
$a=~s/\b +\b/_/gm;
will replace a word break ( \b, a zero-width transition between a word and a non word) followed by one or more spaces followed by an other word break, by an underscore. Using \b ensures that you don't replace a space after or before a new line.
mirod
2010-06-02 12:34:51
Please don't use `$a` or `$b` in examples unless it involves [sorting](http://perldoc.perl.org/perlvar.html).
Zaid
2010-06-02 13:45:17
`$a` was used in the question (and in your answer!). For the spectators here, `$a` and `$b` are "predeclared" in Perl, so you can use it in sort routines under `strict`. I have never been sure why that made it bad to use them anywhere else though.
mirod
2010-06-02 14:02:31
I see where you got the `$a` from, looks like Chas took care of it. And I could've sworn I used `$s`! ;)
Zaid
2010-06-02 14:16:16
+2
A:
This question wouldn't be complete without an answer involving explicit look-ahead and look-behind assertions:
$s =~ s/(?<=\w) (?=\w+)/_/g
This is effectively the same as the solutions involving the zero-width word-boundary anchor,
\b.Note that look-ahead regexes can match regexes of any character length, but look-behind regexes have to be of fixed-length (which is why
(?<=\w+)can't be done).
Zaid
2010-06-02 13:28:34
+1. I've never really used the look-ahead and look-behind assertions that much. Thanks.
Noufal Ibrahim
2010-06-02 14:09:41