Echo value from reassigned variable in linux

Question

I'm newly writing a bash script. I have a configuration file that sets some variables:

environment_information.conf

SIT_SERVER_IP=xxx.xx.xx.xx
SIT_SERVER_PASSWORD=******

I read the conf file and try to echo with predefined keys

echo $SIT_SERVER_IP
echo $SIT_SERVER_PASSWORD

It is working fine without any problem. In my scenario, I will read the values when executing a shell script.

automation_script.sh

#!/bin/sh
. ./environment_information.conf
environment_name=$1"_SERVER_IP";
# test="${environment_prefix}";  # Error
test="${environment_name}";
echo "$.$test";
echo $SIT_SERVER_IP

I tried to get value from conf using input and some constant value:

$ ./automation_script.sh SIT
$.SIT_SERVER_IP
xxx.xx.xx.xx
$

It always prints SIT_SERVER_IP string.

But I'm expecting value from conf file for this SIT_SERVER_IP .

Answer 1

I think you're looking for indirect expansion (paragraph 4 of Shell parameter expansion ):

test=${!environment_name}

This expands to the value of the variable whose name is held in $environment_name .

---

Proof of concept script, loosely based on your code ( automation_script.sh ):

: "${1:?}"  # Check that a parameter (SIT) was passed.

#. ./environment_information.conf
SIT_SERVER_IP="192.10.29.31"   # Surrogate for configuration file
SIT_SERVER_PASSWORD="secret"   # Surrogate for configuration file

echo "SIT_SERVER_IP=${SIT_SERVER_IP}"
echo "SIT_SERVER_PASSWORD=${SIT_SERVER_PASSWORD}"

environment_name="${1}_SERVER_IP"
echo "${environment_name}"
echo "${environment_name}=${!environment_name}"

environment_name="${1}_SERVER_PASSWORD"
echo "${environment_name}"
echo "${environment_name}=${!environment_name}"

Output from running the script:

$ bash automation_script.sh SIT
SIT_SERVER_IP=192.10.29.31
SIT_SERVER_PASSWORD=secret
SIT_SERVER_IP
SIT_SERVER_IP=192.10.29.31
SIT_SERVER_PASSWORD
SIT_SERVER_PASSWORD=secret
$

With the environment_information.conf file from the updated question:

: "${1:?}"

. ./environment_information.conf
#SIT_SERVER_IP="192.10.29.31"
#SIT_SERVER_PASSWORD="secret"

echo "SIT_SERVER_IP=${SIT_SERVER_IP}"
echo "SIT_SERVER_PASSWORD=${SIT_SERVER_PASSWORD}"

environment_name="${1}_SERVER_IP"
echo "${environment_name}"
echo "${environment_name}=${!environment_name}"

environment_name="${1}_SERVER_PASSWORD"
echo "${environment_name}"
echo "${environment_name}=${!environment_name}"

Running that yields:

$ bash automation_script.sh SIT
SIT_SERVER_IP=xxx.xx.xx.xx
SIT_SERVER_PASSWORD=******
SIT_SERVER_IP
SIT_SERVER_IP=xxx.xx.xx.xx
SIT_SERVER_PASSWORD
SIT_SERVER_PASSWORD=******
$