Add options 'Yes,' 'always yes,' 'skip,' 'always skip,' and 'abort' when target file exists

Skip the current file if it already exists without prompting

They're insidious

"Aye-Aye" is in twitch's clip url dictionary. It has a hyphen. The clip URL pattern has been modified to support hyphens.

Highlights:
--all: Download all videos on a channel
--execute-before and --execute-after: Run a command before and after downloading a file, optionally skipping the download when running --execute-before if the script returns non-zero

Other commands added to support my use case.