Basics for Bash CLI Programs
CLI Arguments
Passing arguments or flags is a common way to modify the behaviours of a CLI or extend some particular functionality.
In this code snippet, upon execution, the script will iterate through everything right of the shell argument ($0).
We have facilitated a name and age argument.
./my-cli --name "Keanu Reeves" --age 142
vim my-cli
#!/bin/bash
POS_ARGS=()
# iterate all of the space separated arguments
while [[ $# -gt 0 ]]; do
case $1 in
# single dash and double dash is a shorthand and longhand names for a key: value argument
-n|--name)
name="$2"
shift # continue pass the argument key
shift # continue pass the argument value
;;
-a|--age)
age="$2"
shift # continue pass the argument key
shift # continue pass the argument value
;;
-*|--*)
echo "This key is not an accepted argument $1"
exit 1
;;
*)
POS_ARGS+=("$1") # save positional arg
shift # continue pass the argument value
;;
# esac is to case what fi is to if ;) https://en.wikipedia.org/wiki/ALGOL_68
esac
done
echo ${name}
echo ${age}
Basic Animation
To add a little spice to your CLIs during synchronous operations.
The following creates a little alternating animation between sleep statements.
#!/usr/bin/env bash
while true; do
printf "\r | waiting ..."
sleep 0.25
printf "\r - waiting ..."
sleep 0.25
done
