20180520-parse-arguments-in-bash-script.md

Parse arguments in bash script

Arguments can be passed to a bash script either positionally or with flags.

Positional arguments

Arguments are stored in an 0 based array and can be read via index prepended with a $.

Argument $0 is the name of the script

Using the $@ symbol, we can iterate over the arguments

#!/bin/bash

# store the first argument in variable a
a=$1
# store the second argument in variable b
b=$2

# print a response
echo "Ryu's signature move is the $a$b"

for ARG in "$@"
do
echo "parsed: $ARG"
done

Then call the script with 2 parameters

$ sh ./cool-script.sh 'hadou' 'ken'

Flags

Flags are key / value pairs passed along to the script

#!/bin/bash
move=''

while getopts 'm:v' flag; do
  case "${flag}" in
    m) move="${OPTARG}" ;;
    *) error "Unexpected option ${flag}" ;;
  esac

  echo "Ryu's signature move is the $move"
done

Then call the script as so

$ sh ./cool-script.sh -m 'hadouken'

Links

• getopts tutorial
• How to pass arguments to a bash script