$_='Hello ( World )';
print "$1_$2" if /(\w+) \( (\w+) \)/;
^D
Hello_World
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Interesting. What is the ^d for?

The ^d line was a syntax error on my system, winxp activestate.

What is the ^d for?

It's shorthand for "Control-d", or unix End-of-file character. rupesh was using perl as an interactive processor. (Type "perl" at a command prompt, enter the code, then press "Control-d"). I think windows might use CTRL-z or somesuch, but I don't actually.... care, tbh.

davis

Kids, you tried your hardest, and you failed miserably. The lesson is: Never try.

use strict; use warnings;

my $string = 'Hello (World).';
print join '_', ($string =~ /(\w+)/g);

Prints: Hello_World
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I think this is a job for split+join:

perl -le 'print join "_", split /\W+/, "Hello ( World )"'
Hello_World
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my $string = "Hello ( World ).";
$string =~ s/\(\s*//g; # remove opening bracket followed by spaces
$string =~ s/\s*\)//g; # remove closing bracket preceded by space
$string =~ s/\s/_/g;   # replace spaces still left with underscores
$string =~ s/\.$//;    # remove ending period also
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Presuming any non-word character should be replaced with an underscore:

my $s = 'Hello ( World ).';
$s =~ s/\W+/_/g;  # Replace all sequences of [^a-zA-Z0-9_] with _
$s =~ s/_$//;     # Remove trailing _ if present
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Note that if you wanted to replace strings containing multiple sequential _, you'd have to change \W to the appropriate character class.