Bash file templating function.

README.md

File templating with Bash

Performs the application of given key/value pairs to a source template, with generated results written to an output file.

Functions applyTemplate accepts three arguments:

• Source template file.
• Target output file generated.
• List of key/value pairs as an array.

Example

With the given source template:

Hello, %%COMPUTER%%. Do you read me, %%COMPUTER%%?
Affirmative, %%SPACE_MAN%%. I read you.
Open the pod bay doors, %%COMPUTER%%.
I'm sorry, %%SPACE_MAN%%. I'm afraid I can't do that.

And by calling applyTemplate like so:

applyList=(
	"COMPUTER=HAL" \
	"SPACE_MAN=Dave"
)

applyTemplate \
	"./template.txt" \
	"./output.txt" \
	applyList

We end up with a result in output.txt of:

Hello, HAL. Do you read me, HAL?
Affirmative, Dave. I read you.
Open the pod bay doors, HAL.
I'm sorry, Dave. I'm afraid I can't do that.

applytemplate.sh

#!/bin/bash -e

function applyTemplate {
	# nameref name/value array, create temp file of template
	local -n nameValueList=$3
	local tempFile=$(mktemp)
	cp "$1" "$tempFile"

	# apply each value given
	local nameValueItem
	for nameValueItem in "${nameValueList[@]}"; do
		# split name/value as captures
		if [[ ! $nameValueItem =~ ^([A-Z][A-Z_]+[A-Z])=(.+)$ ]]; then
			continue
		fi

		# escape value for sed call
		local injectValue=$(echo "${BASH_REMATCH[2]}" | sed "s/[\/&]/\\\&/g")

		# apply value to template temp file
		sed \
			--in-place \
			"s/%%${BASH_REMATCH[1]}%%/$injectValue/g" \
			"$tempFile"
	done

	# move temp file to target
	mv "$tempFile" "$2"
	chmod --reference "$1" "$2"
}