Julia 1.9 includes the ability to edit the current input in an editor. Per the 1.9 Release Notes:
Alt-e now opens the current input in an editor. The content (if modified) will be executed upon exiting the editor (#33759).
What is the equivalent shortcut on a Mac?
The documentation says:
The Julia REPL makes great use of key bindings. Several control-key bindings were already introduced above (^D to exit, ^R and ^S for searching), but there are many more. In addition to the control-key, there are also meta-key bindings. These vary more by platform, but most terminals default to using alt- or option- held down with a key to send the meta-key (or can be configured to do so), or pressing Esc and then the key.
"meta key" is a concept familiar to Unix developers. On macs try "pressing and releasing Esc" followed by e