if(   ($SRVCH =~ /\D/) # a non-digit
   || ($SRVCH > 22)    # or greater 22
   ||($SRVCH < 1)      # or smaller than 1
   ||($SRVCH =~ /(\s+)/) # or empty string (but see above)
   ||($SRVCH =~ /[a-zA-Z]/) # or a to z
){ ...