regex

I just can't get over it, it's too hard for me.

match everything after match

the libexec part here is for macOS, you need gnu grep to do -P

/usr/local/opt/grep/libexec/gnubin/grep -oP '/repos/\K.*'

this will match everything after repos/, the K is important here. the .* says that it should match everything afterwards.

remove blank / empty lines

/^[\s]*$\n/

to use it in editors like bbedit, use ^[\s]*$\n

remove blank space end of line

\s+$

google re2 / golang(?)

match foo.example.com and foo-bar.example.com:

(foo|foo-bar|).example.com

you can test your expression here.