bash - using getopts with an associative array in a bash script

Question

I'm using getopts along with an associate array in my code below. What I can't figure out is how to correctly call my values, given that I'm asking for (2) alias(s) using the same flag.

Here's what I have so far:

#!/bin/bash

set -e

usage () {
    echo "Usage: $0 -c alias1  -c alias2"
}

while getopts ":c:" opt; do
  case $opt in
    c) alias="$OPTARG";;
    *) echo "Error unknown option -$OPTARG"
       usage
       exit 1
       ;;
  esac
done

# Testing use off array
declare -A alias=( [alias1]=myhost-01.com \
                   [alias2]=myhost-02.com \
                   [alias3]=myhost-03.com \
                   [alias4]=myhost-04.com )

echo "This is my source host:${alias}"
echo "This is my target host:${alias}"

This is how I would like to execute it (or better suggeested way):

-bash-4.1$ ./test-array2.sh -c alias1 -c alias4
This is my source host:
This is my target host:

Obviously, I'm not getting my expected result which would be this:

This is my source host: myhost-01.com
This is my target host: myhost-04.com

How can I do this? I want to pass in (2) aliases which uses my alias mapping (associative array) to grab the correct key value pair or maybe my approach is wrong and I can't use -c twice? Thanks.

IIRC, array access is ${array[$index]}. So I believe the source would be ${alias[alias1]}, and the target ${alias[alias4]}. I would normally use indices, i.e. 0 insteead of alias1, etc., but that's me. I don't do a lot with Bash, though. — Claudia
– Claudia, Commented Apr 30, 2016 at 17:56
so call it by number on the command line? ./test-array2.sh -c 0 -c3? — noober
– noober, Commented Apr 30, 2016 at 18:15

jil · Accepted Answer · 2016-04-30 18:30:12Z

2

You could use an array to store the aliases e.g.

aliases=()
while getopts ":c:" opt; do
    case $opt in
        c) aliases+=( "$OPTARG" );;
    # ...
    esac
done

And then you use the this array to index your associative array:

echo "This is my source host:${alias_to_host[${aliases[0]}]}"
echo "This is my target host:${alias_to_host[${aliases[1]}]}"

But if the input options are representing aliases for source and destination host and there always is exactly two hosts, it would be much cleaner to use separate options (e.g. -s and -d) and separate variables for these than reusing the switch -c:

# ...
    case $opt in
        s) source=$OPTARG;;
        d) destination=$OPTARG;;
        # ...
    esac
# ...

echo "This is my source host:${alias_to_host[$source]}"
echo "This is my target host:${alias_to_host[$destination]}"

edited Apr 30, 2016 at 18:30

answered Apr 30, 2016 at 18:21

jil

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3 Comments

noober Over a year ago

I agree, using 2 switches would be cleaner. But in my getopts, can I call aliases with two different switches?

jil Over a year ago

Yes, you could still use the same alias_to_host map. Please note that I renamed your original alias associative array to alias_to_host to be more descriptive.

noober Over a year ago

Perfect! Works great. Thanks :-)

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