When I'm using a REPL I generally have all my function definitions in a file I edit in Sublime, which I reload from the REPL, then I just type in commands in the REPL to try out those functions. That way I don't have to copy-paste much, but if you don't like that style I think a Sublime plugin that used Applescript to paste into iTerm2 wouldn't be too hard.

Also for git there is https://github.com/divmain/GitSavvy which is almost as good and sometimes better than magit. There's also terminal git, I generally use a combination of terminal and GitSavvy.