For a standard implementation that may be reused throughout the program:

Example

use Time::localtime;

sub timestamp {
  my $t = localtime;
  return sprintf( "%04d-%02d-%02d_%02d-%02d-%02d",
                  $t->year + 1900, $t->mon + 1, $t->mday,
                  $t->hour, $t->min, $t->sec );
}

print '[' . timestamp() . ']: my message'. "\n";
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Output:

[2011-01-08_11-48-29]: my message
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