I know this is probably a question for the newbie forum, where it is also posted, but I thought maybe some of you pros might like to help me out anyway. Here is my problem:

I have to rename a batch of files that look like:
2001_0001.asc
2001_0002.asc
.
2001_0548.asc
2002_0184.asc
.
.
2006_0548.asc

The names are a date code, but they need to be altered such that 2001_0001.asc becomes 2000_183.asc, 2001_0184 becomes 2001_001, and 2006_0548.asc becomes 2006_365.asc.

so, I think it should start like:

for i in `ls*`
do

then things get a bit hazy
I will now convert to semi-programing speak

split aaaa_bbbb.asc into aaaa and bbbb
interpret strings aaaa and bbbb as numbers x and y respectively
if y - 183 < 1,
then x' = x - 1 and y' = y - 183 + 365,
else x' = x and y' = y - 183.
convert numbers x and y to strings aaaa' and bbb' (note the three digits
in bbb such that y' = 1 will convert to bbb' = 001)
rename file i to aaaa'_bbb'.asc

any help would be appreciated
thanks,
-TT