What is -z in if [ -z "${FILE_LIST}" ]

Question

Came across this, what is -z in the shell script if [ -z "${FILE_LIST}" ]?

Answer 1

[ is the same as test. And man test gives:

   -z STRING
          the length of STRING is zero

Note: On some platforms, [ is a symlink or hardlink to test

Answer 2

From help test:

  -z STRING      True if string is empty.