If you are reluctant to use Date::Manip and Time::Calc because they need to be installed (and you have a problem with that), you could try using Time::Local instead -- this module is part of the core distribution. (update: Happy-the-monk pointed out that it's actually "Date::Calc", not "Time::Calc".)

Time::Local requires a little more work on your part, because you have to split your date string up into its components in order to use the module's "timelocal" function:

use strict;
use Time::Local;

my $time_str = "2004-06-14 13:34:54";

my ($yr, $mo, $dy, $hr, $mi, $sc) = split( /\D+/, $time_str );

$mo--;  # January is supposed to be "month 0"

my $time_unx = timelocal( $sc, $mi, $hr, $dy, $mo, $yr );
  # the function "does the right thing" given a 4-digit year
  # (check the Time::Local man page for more details on that)

# prove that it works:

print "$time_str = $time_unx (" . scalar( localtime $time_unx ) . ")\n
+";
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When I ran that, I got:

2004-06-14 13:34:54 = 1087234494 (Mon Jun 14 13:34:54 2004)