Linux shell: What does -f do?

Question

I have a linux .sh file with something like:

scripts_dir='/opt/myapp/scripts'
[ -f "${scripts_dir}/common.sh" ] && . "${scripts_dir}/common.sh"

scripts_dir defines a variable to represent a directory.

What are we then trying to do in next line?

Answer 1

if child script file exists, run the child script and will update current shell environment of the running script.

Run a shell file in the current environment