The test -a and -o binary operators aren't required on all POSIX systems (but are currently required on a UNIX branded systems). With some expressions -a and -o can lead to ambiguities in the grammar; so they are likely to be deprecated in the next revision of the POSIX standards. (That doesn't mean that they'll every actually be removed from the shells, but the shell developers all advise against using them.)

Fortunately, test and [ are built-ins in current shells so you don't actually have to fork and exec /usr/bin/test twice so the penalty for using test twice isn't nearly as high as it was in early shells.

On OS X (which is what wisecracker is using), both bash and ksh support the command:

Code:

if [[ num >= 100 && num <= 199 ]]

which is handled as part of the shell's grammar, not as a built-in utility (which makes it even faster and gets rid of the ambiguity in the test syntax). This form isn't in the standards yet, but is also likely to be added in the next revision.