getopts: add page (#15237)

pages/common/getopts.md

@@ -0,0 +1,25 @@
+# getopts
+
+> Parse shell options from arguments.
+> This command does not support longform options and thus using `getopt` is recommended instead.
+> More information: <https://www.gnu.org/software/bash/manual/bash.html#index-getopts>.
+
+- Check if an option is set:
+
+`getopts {{x}} {{opt}}; echo $opt`
+
+- Set an option to require an argument and check said argument:
+
+`getopts {{x}}: {{opt}}; echo $OPTARG`
+
+- Check for multiple options:
+
+`while getopts {{xyz}} {{opt}}; do case $opt in x) echo x is set;; y) echo y is set;; z) echo z is set;; esac; done`
+
+- Set `getopts` to silent mode and handle option errors:
+
+`while getopts :{{x:}} {{opt}}; do case $opt in x) ;; :) echo "Argument required";; ?) echo "Invalid argument" esac;; done`
+
+- Reset `getopts`:
+
+`OPTIND=1`