bash-scripting.md

Overview

Setup

#!/usr/bin/env bash

set -u
set -e
set -o pipefail

USAGE="Usage: $(basename "$0") gpr[wbaskvh]

ARGUMENTS
-g              : description of the argument

DEPENDENCIES
aws (cli)

EXAMPLES
Some nice example implementations of this script
"

• set -u: Treat unset variables as an error
• set -e: Exit on an error that isn't scoped by a loop or if statement
• set -x: Show all of the expanded commands in a script as they happen
• set -o pipefail: Exit if any command in a pipeline (like if statement) fails

Parameters

Useful link: https://www.shellscript.sh/tips/getopts/

MY_VAR=false

while getopts 'g:n:wvh' OPTION; do
case $OPTION in
    g)  GIT_REPO="$OPTARG"          ;;
    n)  NAME="$OPTARG"              ;;
    w)  MY_VAR=true                 ;;
    v)  set -x;                     ;;
    [h?]) echo "$USAGE"; exit 0     ;;
esac
done
shift "$((OPTIND - 1))"

: "${GIT_REPO:?}"
: "${NAME:?}"

• 'g:n:wvh': names the flags for this script. Single ones require input, grouped ones are just flags (like tar -xvf my.tar
• g) GIT_REPO="$OPTARG";;: Uses the passed value to set an internal variable
• v) set -x;: sets the -x flag to make this verbose
• [h?]) echo "$USAGE";: outputs the contents of USAGE
• shift "$((OPTIND - 1))": gets rid of the arguments that have been parsed leaving what's left for $1
• : "${NAME:?}": test the named variable has been set up by the script variables

Looping

while

while [ <some test> ]; do
    <commands>
done

for

for var in <list>
do
<commands>
done

break and continue work

source: https://ryanstutorials.net/bash-scripting-tutorial/bash-loops.php

If statements