$ streamlink --show-matchers twitch
- name: player
  pattern: https?://player\.twitch\.tv/\?.+
- name: clip
  pattern: https?://(?:clips\.twitch\.tv|(?:[\w-]+\.)?twitch\.tv/(?:[\w-]+/)?clip)/(?P<clip_id>[^/?]+)
- name: vod
  pattern: https?://(?:[\w-]+\.)?twitch\.tv/(?:[\w-]+/)?v(?:ideos?)?/(?P<video_id>\d+)
- name: live
  pattern: https?://(?:(?!clips\.)[\w-]+\.)?twitch\.tv/(?P<channel>(?!v(?:ideos?)?/|clip/)[^/?]+)/?(?:\?|$)

$ streamlink --show-matchers twitch --json
[
  {
    "name": "player",
    "priority": 20,
    "flags": 0,
    "pattern": "https?://player\\.twitch\\.tv/\\?.+"
  },
  {
    "name": "clip",
    "priority": 20,
    "flags": 0,
    "pattern": "https?://(?:clips\\.twitch\\.tv|(?:[\\w-]+\\.)?twitch\\.tv/(?:[\\w-]+/)?clip)/(?P<clip_id>[^/?]+)"
  },
  {
    "name": "vod",
    "priority": 20,
    "flags": 0,
    "pattern": "https?://(?:[\\w-]+\\.)?twitch\\.tv/(?:[\\w-]+/)?v(?:ideos?)?/(?P<video_id>\\d+)"
  },
  {
    "name": "live",
    "priority": 20,
    "flags": 0,
    "pattern": "https?://(?:(?!clips\\.)[\\w-]+\\.)?twitch\\.tv/(?P<channel>(?!v(?:ideos?)?/|clip/)[^/?]+)/?(?:\\?|$)"
  }
]

$ streamlink --show-matchers hls
- pattern: hls(?:variant)?://(?P<url>\S+)(?:\s(?P<params>.+))?$
- priority: LOW
  flags: IGNORECASE
  pattern: (?P<url>[^/]+/\S+\.m3u8(?:\?\S*)?)(?:\s(?P<params>.+))?$

$ streamlink --show-matchers steam
- pattern: https?://steamcommunity\.com/broadcast/watch/(\d+)
- pattern: https?://steam\.tv/(\w+)

$ streamlink --show-matchers ustreamtv
- flags: VERBOSE
  pattern:
    https?://(?:(?:www\.)?ustream\.tv|video\.ibm\.com)
    (?:
        /combined-embed
        /(?P<combined_channel_id>\d+)
        (?:/video/(?P<combined_video_id>\d+))?
        |
        (?:(?:/embed/|/channel/(?:id/)?)(?P<channel_id>\d+))?
        (?:(?:/embed)?/recorded/(?P<video_id>\d+))?
    )

$ streamlink --show-matchers ustreamtv --json
[
  {
    "name": null,
    "priority": 20,
    "flags": 64,
    "pattern": "https?://(?:(?:www\\.)?ustream\\.tv|video\\.ibm\\.com)\n(?:\n    /combined-embed\n    /(?P<combined_channel_id>\\d+)\n    (?:/video/(?P<combined_video_id>\\d+))?\n    |\n    (?:(?:/embed/|/channel/(?:id/)?)(?P<channel_id>\\d+))?\n    (?:(?:/embed)?/recorded/(?P<video_id>\\d+))?\n)"
  }
]

$ streamlink --show-matchers doesnotexist; echo $?
error: Plugin not found
1

$ streamlink --show-matchers doesnotexist --json; echo $?
{
  "error": "Plugin not found"
}
1