There are some faster solutions which sometimes can be really slow, depending on how many whitespaces a string contain.

If a string contains a lot of whitespaces.
Example: my $str = q{    }. q{a b c d e f g h i j} x 200 . q{    };

MRE book suggests this code:
$str =~ s/^\s+((?:.+\S)?)\s+$/$1/s;

I admit, I was surprised how fast it is compared with: "s/^\s+//" and his brother "s/\s+$//". They can't even compete at a benchmark, they are too slow with the above example! (that's because of the second regex which match at the end of the string, if fails so many times if string contains a lot of whitespaces (see re 'debug')).

Another approach (I know is silly, but is faster in some casses):

$str =~ s/^\s+//;
$str = reverse($str);
$str =~ s/^\s+//;
$str = reverse($str);
[download]

Benchmark using the above example:

's_reverse' 42017/s     --   -12%   -48%
'unpack_A'  47847/s    14%     --   -41%
'MRE_regx'  80645/s    92%    69%     --
[download]

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