Check for empty file in Unix systems

Often, there arises a need to check if a particular file exists and/or is it empty ?, this usually is the scenario when developing shell scripts to automate stuff and a file is created by the script to hold intermediate results. So when the script is scheduled to run next time, it has to execute a sequence of commands if the file exists or it would execute a different set of commands when the file is no longer available.

Here is a simple code snippet which checks for the existence of a file and that it is NOT empty to return TRUE and it returns FALSE otherwise.

if [ -s test_file ]  ### if the test_file exists and that it is not empty
                     ### i.e., file has contents
then
echo "TRUE"          ### returns 'true' ONLY if the file exists and it is NOT empty,
                     ### i.e., file has contents - file is not of 0 bytes in size
else
echo "FALSE"         ### returns 'false' if the file exists and it is empty
                     ### (0 bytes in size).
                     ### returns 'false' also if the file does not exist
fi

For different results to appear, try creating a file 'test_file' and by changing its contents to make it a sized file and/or to make it an empty file.