How to use \W in Regular Expression?

[Sachin]

I would like to use \W in the following program to ignore special character. But it prints "i am perl W+a system"

#!/usr/bin/perl -W
$str = "i am perl: a system"; 
$query = "perl";
$str =~ s/$query\W+/<em>$query<\/em> \W+/ig;

print " Value = " . $str;

[almut]

The substitution part of s/// is not a regular expresssion, so it doesn't make much sense to put \W+ in there.  Just remove it:

$str =~ s/$query\W+/<em>$query<\/em> /ig;

[Sachin]

So could you tell me how to highlight this word "perl" in above program?

[almut]

Not sure what you mean. There's no problem with adding <em>...</em> around the word "perl", it's just the \W+ that's inappropriate in the string to substitute...

Think of it this way: What concrete characters (and how many) should be substituted from the class of characters that \W stands for?

[ikegami]

Is your question really about how to prevent $query="perl"; from matching anything in "This drink is fraperliscious!"?

$str =~ s/\b\Q$query\E\b/<em>$query<\/em>/ig;

or

$str =~ s/(?<!\w)\Q$query\E(?!\w)/<em>$query<\/em>/ig;

[gube]

\W means Match non-word character. As almut said its not required for replace what you are trying to do. Just s/$query/<em>$query</em>/i would be fine. Perl regex