Passing variables to a bash script with default values

Question

I currently have a bash script in which I have hard coded certain variables, and I was hoping to be able to set these variables by passing arguments.

A simple example: consider the script example.sh where I have hard coded values for the variables data_names and run_this

#!/bin/bash

data_names=("apple_picking" "iris")
run_this="TRUE"    

#remainder of script runs things using these hard coded variables

I am wondering if it is possible to edit this script so that:

I can set the values of data_names and run_this by passing arguments when I run bash example.sh
If no arguments are passed for either data_names and run_this to the script, then the variables should take on default (hard coded) values.

Yes, it is possible. What have you tried so far and what happened? — Robert
– Robert, Commented Dec 10, 2014 at 22:14

Gilles Quénot · Accepted Answer · 2014-12-10 22:20:55Z

2

If you want something robust, clear & elegant, you should take a look to getopts to set run_this

Tutorial: http://wiki.bash-hackers.org/howto/getopts_tutorial Examples: http://mywiki.wooledge.org/BashFAQ/035

I think of something like :

./script --run-this=true "apple_picking" "iris"

answered Dec 10, 2014 at 22:20

Gilles Quénot

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2 Comments

Berk U. Over a year ago

Thank you for this! This is the best option by far since it doesn't require input arguments to be specified in a given order / can handle multiple input arguments.

Gilles Quénot Over a year ago

Sure, that's the goal of the proposed solution HTH

anubhava · Accepted Answer · 2014-12-10 22:15:01Z

0

You can use:

#!/bin/bash

# create a BASH array using passed arguments
data_names=("$@")

# if array is empty assign hard coded values
[[ ${#data_names[@]} -eq 0 ]] && data_names=("apple_picking" "iris")

# print argument array or do something else
printf "%s\n" "${data_names[@]}";

answered Dec 10, 2014 at 22:15

anubhava

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Comments

Wrikken · Accepted Answer · 2014-12-10 22:34:09Z

0

Another option is like this:

  run_this=${1:-TRUE}
  IFS=',' read -a data_names <<< "${2:-apple_picking,iris}"

Assuming your script is called like:

 ./script.sh first_argument array,values,in,second,argument

answered Dec 10, 2014 at 22:34

Wrikken

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