Looks like the split is slightly faster:

h:\>perl benchmark.pl
perl benchmark.pl
Benchmark: timing 100000 iterations of trimall_v1, trimall_v2...
trimall_v1: 13 wallclock secs (13.29 usr +  0.00 sys = 13.29 CPU)
trimall_v2: 12 wallclock secs (11.74 usr +  0.01 sys = 11.75 CPU)
[download]

Example code for testing with benchmark:

#!/usr/bin/perl -w

use strict;
use Benchmark;

my $iterations = $ARGV[0] || 100000;

timethese($iterations, {
            trimall_v1 => \&try_trimall_v1,
            trimall_v2 => \&try_trimall_v2,
});


sub try_trimall_v1 {
    my ($val, $list) = setup(); 
    1 for (trimall_v1($val));
    1 for (trimall_v1(@{$list}));
}

sub try_trimall_v2 {
    my ($val, $list) = setup(); 
    1 for (trimall_v2($val));
    1 for (trimall_v2(@{$list}));
}

sub setup {
    my $val="   Scalar  \r\r\n\t\t\n  ";
    my @list=("  List\t\t\n 1 \n \n    \n"," \t\t List 2  ","  List\t\
+t\t\n 3\t\n\n\r  ");
    return $val, \@list;
}


# Using regex
sub trimall_v1 {
    # Trims all extra whitespace from left, right and middle!
    my @out=@_;            # Pass by value!
    for (@out) {
    s/^\s+//;
    s/\s+$//;
    s/\s+/ /g;
    }
    return wantarray ? @out : $out[0];
}

# Using specialized split on ' ' and $_
sub trimall_v2 {
    # Trims all extra whitespace from left, right and middle!
    my @out=@_;            # Pass by value
    for (@out) {
    $_= join ' ',split;
    }
    return wantarray ? @out : $out[0];
}
[download]

Update: Argh ... too late ...

Christian Lemburg
Brainbench MVP for Perl
http://www.brainbench.com