Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

Although the simplest approach would seem to be:

    $string =~ s/^\s*(.*?)\s*$/$1/;

This is unneccesarily slow, destructive, and fails with embedded newlines. It is much better faster to do this in two steps:

    $string =~ s/^\s+//;
    $string =~ s/\s+$//;

Or more nicely written as:

    for ($string) {
        s/^\s+//;
        s/\s+$//;
    }

This idiom takes advantage of the foreach loop's aliasing behavior to factor out common code. You can do this on several strings at once, or arrays, or even the values of a hash if you use a slide:

    # trim whitespace in the scalar, the array, 
    # and all the values in the hash
    foreach ($scalar, @array, @hash{keys %hash}) {
        s/^\s+//;
        s/\s+$//;
    }