Bash Scripting Quick Reference

#!/usr/bin/env bash
set -euo pipefail

chmod +x script.sh

./script.sh

name="Ada"   # no spaces around =

echo "Hi $name"

today=$(date +%F)

read -rp "Name: " name

count=$((count + 1))

(( total += n ))

$1 $2 $3

"$@"   # all, safely quoted

$#

name="${1:-world}"

: "${1:?usage: $0 <file>}"

$0

dir="$(cd "$(dirname "$0")" && pwd)"

if [[ $n -gt 10 ]]; then
  echo big
elif [[ $n -eq 10 ]]; then
  echo ten
else
  echo small
fi

[[ $a == "$b" ]]

[[ -z $s ]]   # empty

[[ -n $s ]]   # not empty

[[ -f file ]]   # file exists

[[ -d dir ]]    # directory exists

-eq -ne -lt -le -gt -ge

case "$1" in
  start) start ;;
  stop)  stop ;;
  *)     echo "usage" ;;
esac

for name in ada grace linus; do
  echo "$name"
done

for f in *.txt; do
  echo "$f"
done

for i in {1..5}; do echo $i; done

for ((i=0; i<5; i++)); do echo $i; done

while IFS= read -r line; do
  echo "$line"
done < input.txt

greet() {
  local name=$1
  echo "Hello, $name"
}
greet Ada

files=(a.txt b.txt)

"${files[@]}"

${#files[@]}  # length

${#s}

${s:0:3}

${s/old/new}

${s//old/new}  # all

${file%.txt}

${path##*/}   # basename

${s^^}

${s,,}

$?

echo "failed" >&2
exit 1

trap 'rm -f "$tmp"' EXIT