16.3.4 String tests

These options test string characteristics. You may need to quote string arguments for the shell. For example:

test -n "$V"

The quotes here prevent the wrong arguments from being passed to test if ‘$V’ is empty or contains special characters.

-z string

True if the length of string is zero.

-n string
string

True if the length of string is nonzero.

string1 = string2

True if the strings are equal.

string1 == string2

True if the strings are equal (synonym for =).

string1 != string2

True if the strings are not equal.