It doesn't actually sound like those are Julian dates that you've got there(1), but days of the year.

Assuming that I'm right, you could try something like this:

use Time::Local;

my $date = '00250';
my ($yr, $day) = unpack('A2A3', $yr);

# Ugly hack to get round the fact that you have 
# two digit dates. Adjust cutoff to taste.
$yr += 100 if $yr < 70;

# Get epoch time at start of year.
my $when = timelocal(0, 0, 0, 1, 0, $yr);

# Increment by number of days
$when += 86_400 * $day;

# Convert back to MMDD
my ($d, $m) = (localtime($when))[3, 4];
++$m;

sprintf('%02d%02d', $d, $m);
[download]

(1) See http://www.treasure-troves.com/astro/JulianDate.html for more stuff about Julian dates.

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<http://www.dave.org.uk>

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