Added getopts post

content/posts/getopts.md

@@ -0,0 +1,42 @@
+---
+title: "CLI flag handling in Bash using getopts"
+date: 2021-08-04T20:49:37+01:00
+draft: false
+tags:
+  - bash
+images:
+- https://opengraph.cluster.fun/opengraph/?siteTitle=Today%20I%20learnt...&title=CLI%20flag%20handling%20in%20Bash%20using%20getopts&tags=bash&image=https%3A%2F%2Fmarcusnoble.co.uk%2Fimages%2Fmarcus.jpg&twitter=Marcus_Noble_&github=AverageMarcus&website=www.MarcusNoble.co.uk
+---
+
+I'm not sure how I've never come across this before but while looking through the [Scaleway Kosmos](https://www.scaleway.com/en/betas/#kuberneteskosmos) multi-cloud init script I dicovered the [`getopts`](https://www.man7.org/linux/man-pages/man1/getopts.1p.html) utility.
+
+`getopts` makes it easier to parse arguments passed to a shell script by defining which letters your script supports. It supports both boolean and string style arguments but only supports single letter flags. (e.g. `-h` and not `--help`)
+
+Example usage:
+
+```sh
+#!/bin/bash
+
+NAME="World"
+FORCE=false
+
+showHelp() {
+    echo "Usage: example.sh [args]"
+    exit 0
+}
+
+while getopts 'hfn:' FLAG
+do
+  case $FLAG in
+    h) showHelp ;;
+    f) FORCE=true ;;
+    n) NAME=$OPTARG ;;
+    *) echo "Unsupported argument flag passed" ;;
+  esac
+done
+
+echo "Hello, $NAME"
+
+```
+
+Notice the `:` following the `n`? That indicates that a value should follow the argument flag (`n` in this example) and will be made available as the `OPTARG` variable.