how to match sub conditions occurring once using regex? - regex

Question

Hi every body i'm trying to match the following condition using regex:
string start with P
followed by one of the following:-
-------- & OR number from 0-9 followed by D occurs once
--------& OR number from 0-9 followed by M occurs once
--------& OR number from 0-9 followed by Y occurs once
--------& OR T followed by one of the following:-
------------------------------------------ & OR number from 0-9 followed by H occurs once
------------------------------------------ & OR number from 0-9 followed by M occurs once
------------------------------------------ & OR number from 0-9 followed by S occurs once
i try to use the following with success:-
P?(([0-9]{1,}D)|([0-9]{1,}M)|([0-9]{1}Y)|(T?(([0-9]{1,}H)|([0-9]{1,}M)|([0-9]{1,}S))))
but it match any given number of any condition i addressed before
any idea how i can achieve this regex condition ?
Edit
lastly i found what i'm looking for
/^P(?=\w*\d)(?:\d+Y|Y)?(?:\d+M|M)?(?:\d+W|W)?(?:\d+D|D)?(?:T(?:\d+H|H)?(?:\d+M|M)?(?:\d+(?:\­.\d{1,2})?S|S)?)?$/

Answer 1

I'm not sure I fully understand your spec, but is this getting close?
P([0-9]+D)?([0-9]+M)?([0-9]+Y)?(T([0-9]+H)?([0-9]+M)?([0-9]+S)?)?
Everything is optional except the leading P, order matters, each section can occur only
once, and the number of digits used in each case is one or more. T is required if anything
after it is included.
The RE above matches "P" and "PT", while the spec presumably requires at least one of the optional components to follow P and T. Using lookahead with grep -P (for Perl regular expressions), we can require P to be followed by a digit.
$ RE='P(?=[0-9])([0-9]+D)?([0-9]+M)?([0-9]+Y)?(T(?=[0-9])([0-9]+H)?([0-9]+M)?([0-9]+S)?)?'
$ for s in P1DT5S P1DT5 P1DT P1D P1 P
do
printf "%-10s %s\n" $s $(echo $s | grep -P -o $RE)
done
P1DT5S P1DT5S
P1DT5 P1DT
P1DT P1D
P1D P1D
P1 P
P
$