Regex in KornShell

Question

I am trying to check whether a variable is exactly two numbers but I can not seem to figure it out.

How do you do check regular expressions (regex) in KornShell (ksh

Answer 1

Where I come from, this is more likely to validate numeric months:

if (( $month >= 1 && $month <= 12 ))

or

[[ $month =~ ^([1-9]|1[012])$ ]]

or to include a leading zero for single-digit months:

[[ $month =~ ^(0[1-9]|1[012])$ ]]