Make a Shell Script with Arguments (Native)

Posted by in Software, Tutorial

I was building a bash script and I needed several arguments to make it more versatile (e.g. dry-run). The list of parameters was:

  • help as -h or --help
  • dry run ad -d or --dry-run to go through the motions without actually executing commands
  • keep last N images ad -k num or --keep num to keep last N images (default 5)

As one can see, none of the parameters are compulsory and have default values:

The snipped taking care of my input parameters is:

The idea is that we loop through all script arguments and shift accordingly. Since the parameters are space separated, we shiftonce for flags without parameters (e.g. --help) and twice for flags with parameters (e.g. --keep).

Once the input parameters are processed, all variables are initialised accordingly.

Note: If you have compulsory parameters, you’ll need to check their presence (e.g. via a variable initialised empty) before further processing.

Help

It’s good to add a help function. Some languages like python have arguments modules with advanced processing and generate help information by default. Unfortunately, the exclusive-shell variant doesn’t do that (unless you want to over-engineer) and you need to do it manually. I ended up having a function like:

This function can be called from the shell processor:


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