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?

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From help test:

  -n STRING
     STRING      True if string is not empty.

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-n tests for a non-zero-length string

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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}" ]