How to read a file in shell, fill its variables from exports, and rewrite it to a new file?

Asked Jul 15 '21 at 11:21

Active Jul 15 '21 at 11:21

Viewed 26 times

Let's say I have this file:

/temp/original_file.txt

The content of this file is:

Hello $FirstName, you have to accomplish $Task

I need to read this file, set variables dynamically, and write the result in a new file. For example if FirstName=Jack and Task=Cooking, and the new file is located in /temp/new_file.txt, the content of the new file would be:

Hello Jack, you have to accomplish Cooking

How can I achieve this in shell?

asked Jul 15 '21 at 11:21

Hossein Fallah

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https://stackoverflow.com/a/17030953/9072753 does https://stackoverflow.com/questions/415677/how-to-replace-placeholders-in-a-text-file answer your question? – KamilCuk Jul 15 '21 at 11:24
You find a proper templating tool. – chepner Jul 15 '21 at 11:37
@chepner, I only want to use shell. – Hossein Fallah Jul 15 '21 at 11:54
@KamilCuk, it seems that `eval` might help. I'm testing those answers. – Hossein Fallah Jul 15 '21 at 11:54
Eval is evil. Use `envsubst`. – KamilCuk Jul 15 '21 at 13:02
Does this answer your question? [How to replace ${} placeholders in a text file?](https://stackoverflow.com/questions/415677/how-to-replace-placeholders-in-a-text-file) – KamilCuk Jul 16 '21 at 08:24
Yeah, https://stackoverflow.com/a/17030953/16304630 helped me. But I had to change it a little bit. Basically it goes `envsubst < original_file_path > target_file_path` – Hossein Fallah Jul 16 '21 at 08:26

How to read a file in shell, fill its variables from exports, and rewrite it to a new file?

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