Doing it in one line while removing leading whitespace is trickier. There are several potentially nasty regular expressions. Just say no.

Update: Squashing several expressions onto one line technically counts, but it wasn't what I meant, smart guy!

$str = '  say  as  simple  as  a   b   c  :-)  ';
$str =~ s/^\s+|\s+$//g, $str =~ tr/ /_/s, print $str;
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$str= "   perlmonks   is   the   coolest";
$str =~ s/\s+/_/g;
print $str;
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(I left out the i modifier because space is the same in capital or lower-case. I don't think that would change the behavior, though!)

—John

Agreed, it works exactly as r.joseph presented it. However you may want to think about using

$str =~ s/ +/_/g;
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instead, since it doesn't mess with your newline characters. That is, with your version "perl\n" becomes "perl_".

- Boldra

This uses the magical whitespace arg to split:

my $str = "  Perlmonks   is  the\tcoolest\n \tplace";
$str = join "_", split " ", $str;
print $str,$/;
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After Compline,
Zaxo

Not recommended but TIMTOWTDI requires someone post this ;-)

$str ='   Perlmonks is     a      very    cool place  ';
$str = join '_', split /\s+/, $str;
print $str;
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cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

you could also use the magical ' ' (single space) arg to split, which will remove leading spaces as well...

#!/usr/bin/perl -wT
use strict;

my $str ='   Perlmonks is     a      very    cool place  ';
$str = join '_', split ' ', $str;
print $str, "\n";

=OUTPUT
Perlmonks_is_a_very_cool_place
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-Blake

Thanks blakem that null string that you get using /\s+/is a pain. I never realised that ' ' was magical.

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

$str = '   xx  y    z  ';
$str =~ s/(?<=\w)\s+(?=\w)/g;  #replace only spaces between letters
$str=~ tr/ //d; #delete leading and trailing spaces
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pike

1 while $str =~ s/[ ]+/_/;
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1 while $str =~ s/[ ]+/ _ /;
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