$text =  "   The   perl      ";
# remove leading whitespace
$text =~ s/^\s+//;
# remove trailing whitespace
$text =~ s/\s+$//;
[download]

$text =~ 
  s{         # Substitute
     \A      #   from the beginning of the string
     \s+     #   one or more white space characters
   }{}xms;  # with nothing

$text =~ 
  s{         # Substitute
     \s+     #   one or more white space characters
     \z      #   from the end of the string
   }{}xms;   # with nothing

$text =~ 
  s{         # Substitute
     \s+     #   one or more white space characters
   }{ }gxms; # with one space, anywhere in the string
             # As many times as it occurs
[download]

Modified my code to address multiple white spaces in the middle of the string and remove white space from the front of the string. This is a little more verbose than the previous poster but I tried to comment each piece to explain it better.

Here's an idiomatic way,

my $text = '   The   perl      ';

$text = join ' ', split ' ', $text;
[download]

If you view the OP's HTML source, you'll see he actually asked:

i should get output as "The   perl"

and not

i should get output as "The perl"

Your solution doesn't answer his question (although that's not your fault).

$text =~ s/(^\s+|\s+$)//g
[download]

RESIST THE URGE! Seriously, don't do that. It slows the whole thing down like you wouldn't believe.

---

Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart

It does? Why's that, then?

-- Tanalis
#include www.liquidfusion.org.uk

A noncapturing solution should speed things.
untested:

s/(?:^\s+)|(?:\s+$)//g
[download]

thanks monks.

Nice, never occurred to me to use join split for that task.

Though using s/// seems to be noticeable faster, at least if not used with an alternating regex:

Update, in reaction to ikegami's reply:

My above code is seriously flawed. Not only the unprovoked change from + to *, but moreso in forgetting the mandatory g modifier in the regex with alternation which should trim the start and the end of the argument string!

Should have told me something, that the version with the worse reputation scored best!

So here comes my corrected and expanded try:

Which gives on this machine:

Short string:
            Rate     2-s    2-sp  2-sp_r     3-s  3-sp_r    3-sp j-spl
+it
2-s     114468/s      --    -14%    -26%    -28%    -42%    -47%    -4
+7%
2-sp    132675/s     16%      --    -14%    -17%    -33%    -38%    -3
+8%
2-sp_r  155014/s     35%     17%      --     -3%    -21%    -28%    -2
+8%
3-s     159352/s     39%     20%      3%      --    -19%    -26%    -2
+6%
3-sp_r  196609/s     72%     48%     27%     23%      --     -8%     -
+9%
3-sp    214344/s     87%     62%     38%     35%      9%      --     -
+0%
j-split 214880/s     88%     62%     39%     35%      9%      0%      
+--

Long string:
           Rate     2-s    2-sp     3-s j-split  2-sp_r    3-sp  3-sp_
+r
2-s      1961/s      --     -3%    -37%    -76%    -77%    -83%    -85
+%
2-sp     2029/s      3%      --    -34%    -76%    -76%    -83%    -85
+%
3-s      3092/s     58%     52%      --    -63%    -63%    -74%    -77
+%
j-split  8343/s    325%    311%    170%      --     -1%    -29%    -38
+%
2-sp_r   8443/s    331%    316%    173%      1%      --    -28%    -38
+%
3-sp    11694/s    496%    476%    278%     40%     39%      --    -13
+%
3-sp_r  13512/s    589%    566%    337%     62%     60%     16%      -
+-
[download]

Why did you convert the "+"s to "*"s? That slows things down greatly (24% for $short, 74% for $long).

               Rate   triple-s  triple-sp
triple-s   122303/s         --       -24%
triple-sp  160627/s        31%         --

              Rate   triple-s  triple-sp
triple-s    2337/s         --       -74%
triple-sp   8991/s       285%         --
[download]

That surprised me, honestly. I only expected it to help when there were no leading/trailing spaces.

You can probably speed up the "_r" versions a little by removing unnecessary "+"s. For example, change

            $str =~ s/\s+/ /g;
            $str =~ s/^\s+//;
            $str =~ s/\s+$//;
[download]

to

            $str =~ s/\s+/ /g;
            $str =~ s/^\s//;
            $str =~ s/\s$//;
[download]

Update: The improvement is quite substantial. Without the +, it ties 3-sp for fastest for short strings, and it's 42% faster than second fastest for long strings.

Short string:
            Rate   3-sp_r 3-sp_r2  3-sp
3-sp_r  329182/s       --    -14%  -14%
3-sp_r2 382305/s      16%      --   -1%
3-sp    384541/s      17%      1%    --

Long string:
           Rate   3-sp 3-sp_r 3-sp_r2
3-sp    20911/s     --   -12%    -38%
3-sp_r  23687/s    13%     --    -29%
3-sp_r2 33582/s    61%    42%      --
[download]