Check for IP validity

Question

How do I check the validity of an IP address in a shell script, that is within the range 0.0.0.0 to 255.255.255.255?

Answer 1

The typical solutions for this all seem to use regular expressions, but it occurs to me that it might be a better approach to do something like:

if echo "$ip" | { IFS=. read a b c d e;
    test "$a" -ge 0 && test "$a" -le 255 &&
    test "$b" -ge 0 && test "$b" -le 255 &&
    test "$c" -ge 0 && test "$c" -le 255 &&
    test "$d" -ge 0 && test "$d" -le 255 &&
    test -z "$e"; }; then echo is valid; fi