在bash脚本中一次运行多个循环

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

Answer 1

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

Answer 2

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