Add text to the beginning of every file

While converting a JavaScript create-react-app project to TypeScript, I wanted a single line of text to every .tsx file. Searching for an answer brought me to this question on StackExchange, specifically this answer.

Using echo and cat, you can add new text to the old file's contents and send it to the original file. Combined with a for loop to iterate over the matching files, I came up with a one-liner^[1] that saved me a lot of time:

for f in **/*.tsx; do echo "// @ts-nocheck
$(cat "$f")" > "$f"; done

This script looks for all .tsx files in any directory, then adds // @ts-nocheck and a newline to the beginning of the file. But there is nothing magic about the selector or added text; you can use whatever you want for those values.

Hope that saves you a bit of time too!

Happy scripting!