Append file content to the source file

Soak up the input before writing the output file.
More information: <https://manned.org/sponge>.
Trick copyright: tl;dr; <https://github.com/tldr-pages/tldr>

cat {{path/to/file}} | sponge -a {{path/to/file}}

click the source code to copy install sponge on any operating system with command-not-found.com