Regular Expression Help

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks!
Can anyone explain to me why this regular expression is not giving me the last print without the spaces on the name and instead it is literally printing the "\s+", why?

#!/usr/bin/perl 

use strict;

use CGI::Carp qw(fatalsToBrowser);
use CGI qw(-oldstyle_urls :standard);

print header();


my $name = 'Joe Doe';

print "Name 1 = $name<br>"; #print "Joe Doe"

$name=~s/\s/_/;

print "Name2 = $name<br>"; #print "Joe_Doe"

$name =~s/_/\s+/;

print "Name 3 = $name<br>"; #print "Joes+Doe"
[download]

Thanks for the help!

Comment on Regular Expression Help Download Code

Replies are listed 'Best First'.
Re: Regular Expression Help by jwkrahn (Abbot) on Aug 23, 2006 at 17:52 UTC
\s is a character class that represents whitespace and it is used in regular expressions. In the substitution operator the left-hand side is a regular expression and the right-hand side is a string and \s in a string is just the character 's'.	[reply]
Re^2: Regular Expression Help by duckyd (Hermit) on Aug 23, 2006 at 18:14 UTC
Building on this, you probably want: `s/_/ /g` [download]	[reply] [d/l]
Re: Regular Expression Help by Fletch (Bishop) on Aug 23, 2006 at 17:50 UTC
Because the right hand side is (baring options to the contrary) basically a double quoted string and is interpreted thusly.	[reply]
Re: Regular Expression Help by graff (Chancellor) on Aug 24, 2006 at 02:41 UTC
`$name =~s/_/\s+/;` [download] Well, that's a bit silly, isn't it? You should understand that "\s+" in the left (regex-match) side of the s/// operator is supposed to mean "match one or more of any kind of white space character". And the right (replacement string) side of the s/// operator is supposed to say exactly what should replace the match. So the reason why "\s+" can't do what you meant as part of the replacement string is: it doesn't say exactly what sort of white space character(s) -- or how many -- should replace the matched string. The same concept applies to any character-class, quantifier or grouping symbol used in a regex match: there's no way they can have the same meaning as replacement strings -- rather than being meaningless, they are simply taken "literally".	[reply] [d/l]
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