A script that works in the folder where you wrote it is not finished. The next person runs it from elsewhere, on a different day, with different files present. Making a script location independent is the step that turns a command you remember into a tool you can hand over.
About 2 min of reading
Make a script location independent.
Write it
Before you run it, say out loud what it will print. Then open the answer.
Run it from two places
Before you run it, say out loud what it will print. Then open the answer.
Resolve paths, check arguments, and set the options that make it stop on failure, all before any work begins. A script whose setup is visible in the first ten lines can be reviewed without running it.
Build the output in a temporary folder and move it into place at the end. If the run fails halfway, the previous good output is still there, which is the difference between a broken deploy and a half written one.
Take the directory the script lives in rather than the directory you are standing in. Then the paths inside it are the same whether you ran it from the terminal, from another folder, or from a build tool.
Take the input path as an argument with a default, and check it exists. A script that assumes a filename will be there fails silently the month the file is renamed.
If a script writes into a folder, confirm the folder is the one it expects before writing. One check at the top prevents the run that put a hundred files in the wrong directory.
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.