I wrote some benchmark code to test the popular answers, and a method using just pattern match and capture instead of s///. I got good results from my pattern match, so I tried plugging my pattern into Daddio's solution (s-capture), and got a significant speedup of it (s-capture2), but still not as good as just using m//. 
use Benchmark 'cmpthese';
use Regexp::Common 'whitespace';

my $f = '   this is a string with  spaces  to    remove      ';
cmpthese(-3, {
  'Regexp-Common' => sub { $_=$f; s/$RE{ws}{crop}//g;    },
  'two-s///'      => sub { $_=$f; s/^\s+//; s/\s+$//;    },
  'one-s///'      => sub { $_=$f; s/^\s+|\s+$//g;        },
  's-capture'     => sub { $_=$f; s/^\s*(.*?)\s*$/$1/;   },
  's-capture2'    => sub { $_=$f; s/^\s*(\S+(?:\s+\S+)?)?\s*$/$1/; },
  'm-capture'     => sub { $_=$f; ($_) = /(\S+(?:\s+\S+)?)/;    },
});

[download]
                 Rate Regexp-Common s-capture one-s/// s-capture2 m-ca
+pture two-s///
Regexp-Common   659/s            --      -91%     -93%       -95%     
+ -96%     -97%
s-capture      7002/s          963%        --     -21%       -45%     
+ -59%     -73%
one-s///       8857/s         1244%       26%       --       -30%     
+ -48%     -66%
s-capture2    12699/s         1827%       81%      43%         --     
+ -26%     -51%
m-capture     17179/s         2507%      145%      94%        35%     
+   --     -34%
two-s///      25941/s         3837%      270%     193%       104%     
+  51%       --

[download]
Not surprisingly, the straightforward method of calling s/// twice is the fastest. What is surprising is how slow Regexp-Common turns out to be, and I was pleasantly surprised at how well m-capture did. If, for some bizarre reason, you needed a single atomic expression to remove leading and trailing whitespace, that would seem to be the way to go.

In reply to Re: How do I remove whitespace at the beginning or end of my string? by Roy Johnson
in thread How do I remove whitespace at the beginning or end of my string? by vroom

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