This task can be done very fast (if not very elegantly) using
Shell Parameter Expansion with the shell configured for "extended globbing"
Code:
c@CW8:~$ string='./DAT000728-652523058.job'
c@CW8:~$ shopt -s extglob
c@CW8:~$ string=${string##*([^0-9])}
c@CW8:~$ echo $string
000728-652523058.job
c@CW8:~$ string=${string%%-*}
c@CW8:~$ echo $string
000728
c@CW8:~$ string=${string##*(0)}
c@CW8:~$ echo $string
728
Alternatively, if the character positions are fixed and only 3 digits are required
Code:
c@CW8:~$ string='./DAT000728-652523058.job'
c@CW8:~$ number=${string:8:3}
c@CW8:~$ echo $number