What does -n in if [ -n "${TEMP_FILE_LIST}" ] do?

What does -n in if [ -n "${TEMP_FIL开发者_运维问答E_LIST}" ] do for this shell script?

From help test:

  -n STRING
     STRING      True if string is not empty.

-n tests for a non-zero-length string

if [ -n "${TEMP_FILE_LIST}" ] 

tests if the argument "${TEMP_FILE_LIST}" does not have zero length.

You can also check

if [ ! -z "${TEMP_FILE_LIST}" ]