Creating an Easy Lookup Table in a UNIX or Linux Shell Script

A Script for Loading a Group of Variables with Environment-specific Values

As a Configuration Manager, I'm always looking for ways to improve the automation of the builds and deployments of my company's applications. We use scripts to compile the apps, replace certain token strings with environment-specific values, and copy the new executable code out to the production servers. Ideally, we should not have to use separate scripts when deploying to different run-time environments (development, integration test, production, etc.). We want instead to pass the target environment into these scripts, and use logic to determine environment-specific values. So I set out to create a Lookup Table to set the values according to the target environment.

I wanted to keep it simple so maintenance would be easy. I wanted it to run in a basic command shell (I use 'bash', but most other shells would work as well). UNIX and linux utilities like 'sed', 'awk,' and various xml parsers would have done the job, but they added complexity so I stayed away from them (although I did use 'grep'). The listing below is a simplified version of what I came up with. It takes one parameter representing the target environment, and sets 3 variables: the target server, the target database, and a process user ID. It then prints the new values to the screen for verification (an optional step). In reality, the unsimplified version of this script also defines target directories, service names, and website urls among other things, but this is enough to give you the idea:

Listing 1#!/bin/bash
# Sets environment variables based on lookup string
# Environments: DEV = Development, QA = Quality Assurance,
# UAT = User Acceptance Test, PROD = Production
ENVIRONMENT=$1

# Set server addresses, database names, and user IDs.
line=`grep ^$ENVIRONMENT --- ------------------------ --------- ----------
DEV dev.myapp.mybusiness.com myappdev devappuser
QA qa.myapp.mybusiness.com myappqa qaappuser
UAT uat.myapp.mybusiness.com myappuat uatappuser
PROD prod.myapp.mybusiness.com myappprod prodappuser
EOF`