https://www.computerhope.com/unix/test.htm

Note: Some shells also accept "==" for string comparison; this is NOT portable, 
a single "=" should be used for strings, and "-eq" for integers.

if [ "$a" = "myString" ] # note [ is test
test 100 -gt 199 && printf "100>99\n" || printf "less"

string OP
	=	note: ==  no good for its bad portability
	!=

int OP
	-ge -gt :great_or_equal greter
	-le -lt :less_or_equal less
	-eq -ne :equal not_equal

Q: mutiple operation using test?
A: using &&
test 5 -gt 4 && printf "5 " && printf "> 4\n"