$ cat >> $HGRCPATH << EOF

  > [extensions]

  > show =

  > EOF

No arguments shows available views

  $ hg init empty

  $ cd empty

  $ hg show

  available views:

  bookmarks -- bookmarks and their associated changeset

  work -- changesets that aren't finished

  abort: no view requested

  (use "hg show VIEW" to choose a view)

  [255]

`hg help show` prints available views

  $ hg help show

  hg show VIEW

  show various repository information

      A requested view of repository data is displayed.

      If no view is requested, the list of available views is shown and the

      command aborts.

      Note:

         There are no backwards compatibility guarantees for the output of this

         command. Output may change in any future Mercurial release.

         Consumers wanting stable command output should specify a template via

         "-T/--template".

      List of available views:

      bookmarks   bookmarks and their associated changeset

      work        changesets that aren't finished

  (use 'hg help -e show' to show help for the show extension)

  options:

   -T --template TEMPLATE display with template

  (some details hidden, use --verbose to show complete help)

Unknown view prints error

  $ hg show badview

  abort: unknown view: badview

  (run "hg show" to see available views)

  [255]

HGPLAIN results in abort

  $ HGPLAIN=1 hg show bookmarks

  abort: must specify a template in plain mode

  (invoke with -T/--template to control output format)

  [255]

But not if a template is specified

  $ HGPLAIN=1 hg show bookmarks -T '{bookmark}\n'

  (no bookmarks set)

  $ cd ..

bookmarks view with no bookmarks prints empty message

  $ hg init books

  $ cd books

  $ touch f0

  $ hg -q commit -A -m initial

  $ hg show bookmarks

  (no bookmarks set)

bookmarks view shows bookmarks in an aligned table

  $ echo book1 > f0

  $ hg commit -m 'commit for book1'

  $ echo book2 > f0

  $ hg commit -m 'commit for book2'

  $ hg bookmark -r 1 book1

  $ hg bookmark a-longer-bookmark

  $ hg show bookmarks

  * a-longer-bookmark    7b570

    book1                b757f

A custom bookmarks template works

  $ hg show bookmarks -T '{node} {bookmark} {active}\n'

  7b5709ab64cbc34da9b4367b64afff47f2c4ee83 a-longer-bookmark True

  b757f780b8ffd71267c6ccb32e0882d9d32a8cc0 book1 False

bookmarks JSON works

  $ hg show bookmarks -T json

  [

   {

    "active": true,

    "bookmark": "a-longer-bookmark",

    "longestbookmarklen": 17,

    "node": "7b5709ab64cbc34da9b4367b64afff47f2c4ee83"

   },

   {

    "active": false,

    "bookmark": "book1",

    "longestbookmarklen": 17,

    "node": "b757f780b8ffd71267c6ccb32e0882d9d32a8cc0"

   }

  ]

JSON works with no bookmarks

  $ hg book -d a-longer-bookmark

  $ hg book -d book1

  $ hg show bookmarks -T json

  [

  ]

  $ cd ..