Use $(< file) instead of $(cat file)

[akihiro17]

I think it's better to use $(< file) instead of $(cat file)

ref. https://www.gnu.org/software/bash/manual/html_node/Command-Substitution.html

The command substitution $(cat file) can be replaced by the equivalent but faster $(< file).

[Mte90]

Tested with shellcheck and it is valid bash:

#!/usr/bin/bash

echo $(< "test")

I learned something new but it is better as it is pure bash.

[Ph0enixKM]

I learned something new as well! Great PR