Mercurial allows you to customize output of commands through
templates. You can either pass in a template or select an existing
template-style from the command line, via the --template option.

You can customize output for any "log-like" command: log,
outgoing, incoming, tip, parents, and heads.

Five styles are packaged with Mercurial: default (the style used
when no explicit preference is passed), compact, changelog, phases
and xml.
Usage::

    $ hg log -r1 --template changelog

A template is a piece of text, with markup to invoke variable
expansion::

    $ hg log -r1 --template "{node}\n"
    b56ce7b07c52de7d5fd79fb89701ea538af65746

Strings in curly braces are called keywords. The availability of
keywords depends on the exact context of the templater. These
keywords are usually available for templating a log-like command:

.. keywordsmarker

The "date" keyword does not produce human-readable output. If you
want to use a date in your output, you can use a filter to process
it. Filters are functions which return a string based on the input
variable. Be sure to use the stringify filter first when you're
applying a string-input filter to a list-like input variable.
You can also use a chain of filters to get the desired output::

   $ hg tip --template "{date|isodate}\n"
   2008-08-21 18:22 +0000

List of filters:

.. filtersmarker

Note that a filter is nothing more than a function call, i.e.
``expr|filter`` is equivalent to ``filter(expr)``.

In addition to filters, there are some basic built-in functions:

- date(date[, fmt])

- fill(text[, width])

- get(dict, key)

- if(expr, then[, else])

- ifcontains(expr, expr, then[, else])

- ifeq(expr, expr, then[, else])

- join(list, sep)

- label(label, expr)

- revset(query[, formatargs])

- rstdoc(text, style)

- shortest(node)

- startswith(string, text)

- strip(text[, chars])

- sub(pat, repl, expr)

- word(number, text[, separator])

Also, for any expression that returns a list, there is a list operator:

- expr % "{template}"

Some sample command line templates:

- Format lists, e.g. files::

   $ hg log -r 0 --template "files:\n{files % '  {file}\n'}"

- Join the list of files with a ", "::

   $ hg log -r 0 --template "files: {join(files, ', ')}\n"

- Modify each line of a commit description::

   $ hg log --template "{splitlines(desc) % '**** {line}\n'}"

- Format date::

   $ hg log -r 0 --template "{date(date, '%Y')}\n"

- Output the description set to a fill-width of 30::

   $ hg log -r 0 --template "{fill(desc, '30')}"

- Use a conditional to test for the default branch::

   $ hg log -r 0 --template "{ifeq(branch, 'default', 'on the main branch',
   'on branch {branch}')}\n"

- Append a newline if not empty::

   $ hg tip --template "{if(author, '{author}\n')}"

- Label the output for use with the color extension::

   $ hg log -r 0 --template "{label('changeset.{phase}', node|short)}\n"

- Invert the firstline filter, i.e. everything but the first line::

   $ hg log -r 0 --template "{sub(r'^.*\n?\n?', '', desc)}\n"

- Display the contents of the 'extra' field, one per line::

   $ hg log -r 0 --template "{join(extras, '\n')}\n"

- Mark the current bookmark with '*'::

   $ hg log --template "{bookmarks % '{bookmark}{ifeq(bookmark, current, \"*\")} '}\n"

- Mark the working copy parent with '@'::

   $ hg log --template "{ifcontains(rev, revset('.'), '@')}\n"

- Show only commit descriptions that start with "template"::

   $ hg log --template "{startswith(\"template\", firstline(desc))}\n"

- Print the first word of each line of a commit message::

   $ hg log --template "{word(\"0\", desc)}\n"