process-template bash script

Simple placeholder replacing tool based on bash which uses environment variables. Used for initialization of docker containers by Lundegaard.

Usage

process-template [-f from-file] [-p placeholder-prefix] [-q] [-v] [-s] -t target-file
    -f | --from from-file      Template file to process. If not given, target is used as input.
    -t | --target target-file  Target file to write the result.
    -p | --prefix pattern      Prefix of the placeholders [Default: PLACEHOLDER_]
    -q | --quiet               Do not output any status messages
    -v | --verbose             Output detailed info including messages from log file
    -s | --strict              Exit with exitcode 4 when some placeholders in template are not in env

Script simply replaces placeholders in the template file with values from environment variables and writes the result into target file.

The script would try to replace all env variables, to avoid conflicts placeholders should have prefix (by default PLACEHOLDER_), so e.g. for env variable PASS is the placeholder PLACEHOLDER_PASS. Prefix is configurable via -p parameter.

If the resulting file still contains placeholders, you might want to fail, since some expected value was not in the env variables. Use -s parameter for this.

Example

We have template in file config.properties.tpl like this:

db.user=PLACEHOLDER_DB_USER
db.pass=PLACEHOLDER_DB_PASS

and the script to generate the config might look like this:

export DB_USER=test
export DB_PASS=mySuperSecret

process-template -f config.properties.tpl -t config.properties

then resulting config.properties file would contain:

db.user=test
db.pass=mySuperSecret

Tests

The script is tested using suite based on:

• https://github.com/sstephenson/bats/
• https://github.com/ztombol/bats-support
• https://github.com/ztombol/bats-assert

All these tools are ready in the docker.lnd.bz/bats:latest docker image.

Test suite can be easily run via the process-template.test.sh script.