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GNU Core-utils

16.3.4 String tests

These options test string characteristics. Strings are not quoted for test, though you may need to quote them to protect characters with special meaning to the shell, e.g., spaces.

`-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 not equal.