@pixellany: I tried man string, but it points to C/C++ functions related to string operations. I've never heard of a string command, except for the command strings to print ascii characters from a binary.
@jkeertir: it depends on how do you want to compare them. In awk the string and numeric comparison operators are the same, so you can use = != > >= and so on. In bash the string comparison is done by = != > >= and so on, whereas the numeric comparison uses -eq -ne -gt -ge and so on.