Take a look at Date::Manip module on CPAN. It can do this and a whole load more.

For your specific problem, the following code:

use Date::Manip;

print UnixDate( ParseDate( "last business day of september 2002"), '%F
+' );
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gives: Monday, September 30, 2002

BTW: It would be easier for thise coming along after you to find the answers already given to your problem if you would make your titles a little more specific to the question you are asking.

Suggestion: "A function to find last business day of the month." - maybe too wordy, but you get the idea :^)

#!/usr/local/perl -w

# Calculate the last business day of the month.

use strict;

my $last_day = _calc_last_day();
print "Last business day of the month: $last_day\n";

sub _calc_last_day {
    use Time::Local;
    use POSIX qw(strftime);

    my ($_year, $_month) = split(/\./, `date +%y.%m`);
    chomp($_year, $_month);

    # Calculate the last day of the month.
    my $_next_year = ($_month == 12) ? $_year + 1 : $_year;
    my $_next_month = timelocal(0, 0, 0, 1, $_month % 12, $_next_year)
+;
    my $_last_day = (localtime($_next_month - 86400))[3];

    # Make sure it is a business day.
    my $_day = strftime "%a", localtime($_next_month - 86400);
    if ($_day eq 'Sat') { $_last_day--; }
    if ($_day eq 'Sun') { for (1..2) { $_last_day--; } }

    return "$_month/$_last_day/$_year";
}
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