replace placeholders in bash

how-to-replace-placeholders-in-a-text-file-using-bash.md

To me this is the easiest and most powerful solution, you can even include other templates using the command eval echo "$(<template.txt):

Example with nested template

1. create the template files, the variables are in regular bash syntax ${VARIABLE_NAME} or $VARIABLE_NAME

you have to escape special characters with \ in your templates otherwhise they will be interpreted by eval.

template.txt

Hello ${name}!
eval echo $(<nested-template.txt)

nested-template.txt

Nice to have you here ${name} :\)

2. create source file

template.source

declare name=royman 

3. parse the template

source template.source && eval echo "$(<template.txt)"

4. the output

Hello royman!
Nice to have you here royman :)