$ streamlink -l debug --plugin-dir /tmp/foo --plugin-dir /tmp/bar --plugin-dirs /tmp/baz,/tmp/qux
[cli][warning] Plugin path /tmp/foo does not exist or is not a directory!
[cli][warning] Plugin path /tmp/bar does not exist or is not a directory!
[cli][warning] Plugin path /tmp/baz does not exist or is not a directory!
[cli][warning] Plugin path /tmp/qux does not exist or is not a directory!
[cli][debug] OS:         Linux-6.7.6-1-git-x86_64-with-glibc2.39
[cli][debug] Python:     3.12.2
[cli][debug] OpenSSL:    OpenSSL 3.2.1 30 Jan 2024
[cli][debug] Streamlink: 6.6.2+6.geef44a16
[cli][debug] Dependencies:
[cli][debug]  certifi: 2024.2.2
[cli][debug]  isodate: 0.6.1
[cli][debug]  lxml: 5.1.0
[cli][debug]  pycountry: 23.12.11
[cli][debug]  pycryptodome: 3.20.0
[cli][debug]  PySocks: 1.7.1
[cli][debug]  requests: 2.31.0
[cli][debug]  trio: 0.24.0
[cli][debug]  trio-websocket: 0.11.1
[cli][debug]  typing-extensions: 4.9.0
[cli][debug]  urllib3: 2.2.1
[cli][debug]  websocket-client: 1.7.0
[cli][debug] Arguments:
[cli][debug]  --plugin-dir=['/tmp/foo', '/tmp/bar', '/tmp/baz', '/tmp/qux']
[cli][debug]  --loglevel=debug
[cli][debug]  --player=/usr/bin/mpv
usage: streamlink [OPTIONS] <URL> [STREAM]

Use -h/--help to see the available options or read the manual at https://streamlink.github.io