Argument defaults in shell scripts

Regularly when writing a shell script I find that I want to be able to pass an argument into the script but only sometimes. For example if I want the script to output to /tmp folder for the most part but I’d like the opportunity to select the output myself.

Default arguments can be used in scripts using the following simple syntax

#!/bin/sh

# example script to write to output folder

OUTPUT_PATH=${1:-/tmp/output}

echo "some arbitrary process" > ${OUTPUT_PATH}/arbitrary_output.output

This will either used the first parameter passed in for the output path or a default value of /tmp/output if that isn’t provided

sh example_script.sh # outputs to /tmp/output

sh example_script.sh /var/tmp/special # outputs to /var/tmp/special