I have long lists as follows:
D6N T69TN K70R M184V T215FEG
The result must be like this:
D006N T069TN K070R M184V T215FEG
I'm new on bash, I tried approaches based in splitting it in columns and reformat. However the positions and length of 2nd and 3rd putative columns are not fixed. Thank you for any help!
You can do this using awk, using the built-in match function:
awk 'match($0, /[0-9]+/) { printf "%s%03d%s\n",
substr($0, 0, RSTART - 1), substr($0, RSTART, RLENGTH), substr($0, RSTART + RLENGTH) }' file
When match is successful, it sets two variables RSTART and RLENGTH, which can be used to extract substrings. The middle substring is formatted using %03d, to pad with leading zeros.
Any lines not matching the pattern won't be printed.
Another option using perl:
perl -pe 's/\d{1,3}/sprintf("%03d", $&)/eg' file
This replaces any sequence of one to three digits with a zero-padded three digit number. In this version, all lines are printed.