Here is the correction to the last paragraph I wrote in post #18...

My code looks for trailing digits to determine the numeric part of your input (allowing other digits to appear elsewhere in the prefix). When there aren't any trailing decimal digits (as with an input line containing "S2<space><space>"), you don't get what you wanted because:

Code:

	NUMBER = substr($0, match($0, /[[:digit:]]*$/))

successfully matches zero decimal digits at the end of the string and saves an empty string in the variable NUMBER and the call to match has the side effect of setting RSTART to the offset in $0 where the first of zero decimal digits was found (5 being the address of the null byte terminating the string) and setting RLENGTH to the number of decimal digits found at the end of the $0 (0 in this case). (If the ERE had been [[:digit:]]+$ which matches one or more decimal digits at the end of the string instead of [[:digit:]]*$ which matches zero of more decimal digits at the end of the string, different problems would arise. This code was designed to work under several assumption including:

Code:

	PREFIX = substr($0, 1, PRELEN = (RSTART - 1))

sets PREFIX to the prefix (your alphabetic part, but this will use the longest string at the start of the line that does not end in a decimal digit). And it sets PRELEN to the length of that string (4 = 5 - 1 in this case).

Code:

	DIGITS = LEN - PRELEN

sets DIGITS to the length of the string you want (8) minus the length of PREFIX (PRELEN), which in this case is 4 (8 - 4).

Code:

	printf "%s%0*d\n", PREFIX, DIGITS, NUMBER

and here we print the PREFIX saved above and uses the same %04d format to print the decimal digits found at the end of your input. And, since there weren't any digits at the end of the string and the awk printf %d specifier treats an empty string as the numeric value zero, it prints the entire input string as the prefix followed by four zeros:

Code:

S2  0000

If I was writing production code, I would test that the input meets the stated assumptions and produce a diagnostic message for that input line instead of producing garbage output from garbage input. If anyone wants to turn sample code provided by the volunteers here at The UNIX & Linux Forums into production code, verifying that input meets the stated input requirements is part of that task. (Note that I stated the input and output assumptions used by my script in post #10 in this thread. When the input meets all of the input assumptions, it produces the desired output. If one or more of those assumptions are not met, I make no claims about the output produced by my sample code as a result.)