twitch-dl/docs/environment_variables.md

Environment variables

Introduced in twitch-dl 2.2.0

twitch-dl allows setting defaults for parameters via environment variables.

Environment variables should be named TWITCH_DL_<COMMAND_NAME>_<OPTION_NAME>.

For example, when invoking twitch-dl download, if you always set --quality source you can set the following environment variable to make this the default:

TWITCH_DL_DOWNLOAD_QUALITY="source"