Running multiple loop at once in bash script

Question

Below is the script that I am running

#!/bin/bash

region=('us-east-1' 'eu-central-1')
env=('prod' 'stage')


for region in "${region[@]}"
do
        for env in "${env[@]}"
        do
                echo "$region"
                echo "$env"
        done
done

The output that I am getting is

us-east-1
prod
us-east-1
stage
eu-central-1
stage
eu-central-1
stage

But my expectation was to get

us-east-1
prod
us-east-1
stage
eu-central-1
prod
eu-central-1
stage

The script should run for both env conditions, but its running only once for prod and thrice for stage. Where am I going wrong here, any pointers or advice would be appreciated

hek2mgl · Accepted Answer · 2021-11-03 08:48:04Z

6

You need to use a different variable for the loop than the initial array. Otherwise you are overwriting the array during the first iteration.

Here I'm using different variables for the array and the loop variable:

#!/bin/bash

regions=('us-east-1' 'eu-central-1')
envs=('prod' 'stage')
    
for region in "${regions[@]}"
do
    for env in "${envs[@]}"
    do
        echo "$region"
        echo "$env"
    done
done

Output:

us-east-1
prod
us-east-1
stage
eu-central-1
prod
eu-central-1
stage

PS: Another option would be to use a string of multiple words and have bash iterating over that:

for a in foo bar
do
    for b in baz qux
    do
        echo "${a}"
        echo "${b}"
    done
done

edited Nov 3, 2021 at 8:48

answered Nov 2, 2021 at 10:23

hek2mgl

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1 Comment

Devops-Learner Over a year ago

Thanks this is the easiest way to do that, apart from that i have included env=('prod' 'stage') within for loop of region. that also helps here

Andreas Louv · Accepted Answer · 2021-11-02 10:21:19Z

4

Arrays and scalar parameters lives in the same namespace, so the scalar will override the array in this example:

$ a=(hello world)
$ a=123
$ echo "${a[@]}"
123

In your example you are overriding the env variable in the inner loop, the execution is the following, in pseudo code:

expand "${region[@]}" into 'us-east-1' 'eu-central-1'
set region 'us-east-1'
expand "${env[@]}" into 'prod' 'stage'
set env 'prod'
... echo ...
set env 'stage'
... echo ...
set region 'us-central-1'
expand "${env[@]}" into 'stage'
...

Consider the following:

$ a="hello"; echo "${a[@]}"
hello

answered Nov 2, 2021 at 10:21

Andreas Louv

47.3k14 gold badges109 silver badges126 bronze badges

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