Creating an Easy Lookup Table in a Shell Script

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 seperate 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’ and ‘awk,’ and xml parsers would have done the job, but they added complexity so I stayed away from them (although I do 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). The script we actually use at work also sets target directories, service names, and website urls, 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 <<EOF

Env Server Database User ID

— ———————— ——— ———-

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`

set — $line

export AppServer=$2

export DataBase=$3

export UserID=$4

#

# Show environment settings:

echo “AppServer = $AppServer”

echo “DataBase = $DataBase”

echo “UserID = $UserID”

Sample run:

$ ./Lookup.sh DEV

AppServer = dev.myapp.mybusiness.com

DataBase = myappdev

UserID = devappuser

$

Using the Technique

Knowing how this script works is not essential to using the technique, as long as you realize that you can expand it by adding more values to the ends of the input lines, and creating enough values with the ‘export’ statements to accomodate the new values.

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