First note that unlike C functions, shell functions can't return negative values. (The exit code from a shell function is a value in the range 0 through 255, inclusive.) Looking at your original script, it uses only two return values: 0 and 77. However, I don't know what the calls to fail do in your script. If they exit, that would exit the shell script that calls your function instead of just returning an error code for your function.

The following replacement for your function assumes that fail is a function that prints a diagnostic message and returns to the caller. (So after calling fail, this version of your function returns a non-zero exit status indicating that the checkversion() function was not able to successfully compare to version strings.) If this version of checkversion() does successfully compare two version strings it returns 0 and sets the variable checkversion_result to an integral value that is zero if the versions are the same, a value greater than zero if the version found in the symbolic link identified by the 1st operand is greater than the version passed in as the 2nd operand, or a value less than zero if the version found in the symlink is less than the version given as the 2nd operand.

All of the command substitutions using cut to find various subfields have been replaced by parameter substitutions (so this should be considerably faster). Debugging printf statements have been added so you can see each test being performed and the values used to determine the final result that is returned. (If the code is giving you values that are appropriate for what you're trying to do, you can remove all of the printf statements that start at the left margin. Note that I am not at all sure that I have the results correct in one, and only one, of the version strings contains RC_.)

This should all work with any shell that performs the parameter expansions required by the POSIX standards. (It has been tested with bash and ksh.) Like your script, it will only work on a system that includes a readlink utility. (The readlink utility is provided by many systems, but is not required by the POSIX standards.)

Code:

checkversion_result=

checkversion() {
	checkversion_result=
	local mod="$1"
	local vers="$2"
	local slink="/app/mes_dwh/$mod/${mod}"
	local target=$(readlink "$slink")
	target=${target#*V}
	target=V${target%%V*}

	case "$target" in
        (V_[0-9]_[0-9]_[0-9]_RC_b* | V_[0-9]_[0-9]_[0-9]_b*)
		;;
        (*)	fail "bad version string: '$target'"
		return 1
		;;
	esac
	case "${target##*b}" in
        (*[!0-9]*)
        	fail "bad build number: '$target'"
		return 2
		;;
	esac
  
	#compare major version
	local old=${target#*_}
	old=${old%%_*}
	local new=${vers#*_}
	new=${new%%_*}
	checkversion_result=$((old - new))
printf 'major old:%s new:%s result:%s\n' "$old" "$new" "$checkversion_result"
	[ "$checkversion_result" -ne 0 ] && return 0
	#compare middle version
	old=${target#*_*_}
	old=${old%%_*}
	new=${vers#*_*_}
	new=${new%%_*}
	checkversion_result=$((old - new))
printf 'middle old:%s new:%s result:%s\n' "$old" "$new" "$checkversion_result"
	[ "$checkversion_result" -ne 0 ] && return 0
	#compare minor version
	old=${target#*_*_*_}
	old=${old%%_*}
	new=${vers#*_*_*_}
	new=${new%%_*}
	checkversion_result=$((old - new))
printf 'minor old:%s new:%s result:%s\n' "$old" "$new" "$checkversion_result"
	[ "$checkversion_result" -ne 0 ] && return 0
	#ocmpare RC_b versus b
	old=${target#*_*_*_*_}
	old=${old%%b*}
	new=${vers#*_*_*_*_}
	new=${new%%b*}
	if [ "$old" != "$new" ]
	then	[ "$old" = "" ] && checkversion_result=1 || \
				   checkversion_result=-1
	fi
printf 'RC old:%s new:%s result:%s\n' "$old" "$new" "$checkversion_result"
	[ "$checkversion_result" -ne 0 ] && return 0
	#compare build version
	old=${target##*b}
	new=${vers##*b}
	checkversion_result=$((old - new))
printf 'build old:%s new:%s result:%s\n' "$old" "$new" "$checkversion_result"
	return 0
}

The way to use this function would be something like:

Code:

if checkversion mod version
then	echo "version check completed successfully, result: $checkversion_result"
else	echo "version check failed; see diagnostics above"
fi