Chapter 11. Customizing the output of Mercurial
Table of Contents
Mercurial provides a powerful mechanism to let you control how it displays information. The mechanism is based on templates. You can use templates to generate specific output for a single command, or to customize the entire appearance of the built-in web interface.
Using precanned output styles
Packaged with Mercurial are some output styles that you can use immediately. A style is simply a precanned template that someone wrote and installed somewhere that Mercurial can find.
Before we take a look at Mercurial's bundled styles, let's review its normal output.
$hg log -r1changeset: 1:107e439be01c tag: mytag user: Bryan O'Sullivan <bos@serpentine.com> date: Tue May 05 06:55:46 2009 +0000 summary: added line to end of <<hello>> file.
This is somewhat informative, but it takes up a lot of
space—five lines of output per changeset. The
compact style reduces this to three lines,
presented in a sparse manner.
$hg log --style compact3[tip] 65efccbd2729 2009-05-05 06:55 +0000 bos Added tag v0.1 for changeset 59abc8be7140 2[v0.1] 59abc8be7140 2009-05-05 06:55 +0000 bos Added tag mytag for changeset 107e439be01c 1[mytag] 107e439be01c 2009-05-05 06:55 +0000 bos added line to end of <<hello>> file. 0 5ce2a492c569 2009-05-05 06:55 +0000 bos added hello
The changelog style hints at the
expressive power of Mercurial's templating engine. This style
attempts to follow the GNU Project's changelog
guidelines[web:changelog].
$hg log --style changelog2009-05-05 Bryan O'Sullivan <bos@serpentine.com> * .hgtags: Added tag v0.1 for changeset 59abc8be7140 [65efccbd2729] [tip] * .hgtags: Added tag mytag for changeset 107e439be01c [59abc8be7140] [v0.1] * goodbye, hello: added line to end of <<hello>> file. in addition, added a file with the helpful name (at least i hope that some might consider it so) of goodbye. [107e439be01c] [mytag] * hello: added hello [5ce2a492c569]
You will not be shocked to learn that Mercurial's default
output style is named default.
Setting a default style
You can modify the output style that Mercurial will use
for every command by editing your ~/.hgrc file, naming the style
you would prefer to use.
[ui] style = compact
If you write a style of your own, you can use it by either
providing the path to your style file, or copying your style
file into a location where Mercurial can find it (typically
the templates subdirectory of your
Mercurial install directory).
Commands that support styles and templates
All of Mercurial's
“log-like” commands let you use
styles and templates: hg
incoming, hg log,
hg outgoing, and hg tip.
As I write this manual, these are so far the only commands that support styles and templates. Since these are the most important commands that need customizable output, there has been little pressure from the Mercurial user community to add style and template support to other commands.
The basics of templating
At its simplest, a Mercurial template is a piece of text. Some of the text never changes, while other parts are expanded, or replaced with new text, when necessary.
Before we continue, let's look again at a simple example of Mercurial's normal output.
$hg log -r1changeset: 1:107e439be01c tag: mytag user: Bryan O'Sullivan <bos@serpentine.com> date: Tue May 05 06:55:46 2009 +0000 summary: added line to end of <<hello>> file.
Now, let's run the same command, but using a template to change its output.
$hg log -r1 --template 'i saw a changeset\n'i saw a changeset
The example above illustrates the simplest possible
template; it's just a piece of static text, printed once for
each changeset. The --template option to the hg log command tells Mercurial to use
the given text as the template when printing each
changeset.
Notice that the template string above ends with the text
“\n”. This is an
escape sequence, telling Mercurial to print
a newline at the end of each template item. If you omit this
newline, Mercurial will run each piece of output together. See
the section called “Escape sequences” for more details
of escape sequences.
A template that prints a fixed string of text all the time isn't very useful; let's try something a bit more complex.
$hg log --template 'i saw a changeset: {desc}\n'i saw a changeset: Added tag v0.1 for changeset 59abc8be7140 i saw a changeset: Added tag mytag for changeset 107e439be01c i saw a changeset: added line to end of <<hello>> file. in addition, added a file with the helpful name (at least i hope that some might consider it so) of goodbye. i saw a changeset: added hello
As you can see, the string
“{desc}” in the template has
been replaced in the output with the description of each
changeset. Every time Mercurial finds text enclosed in curly
braces (“{” and
“}”), it will try to replace the
braces and text with the expansion of whatever is inside. To
print a literal curly brace, you must escape it, as described in
the section called “Escape sequences”.
Common template keywords
You can start writing simple templates immediately using the keywords below.
branches: String. The name of the branch on which the changeset was committed. Will be empty if the branch name wasdefault.date: Date information. The date when the changeset was committed. This is not human-readable; you must pass it through a filter that will render it appropriately. See the section called “Filtering keywords to change their results” for more information on filters. The date is expressed as a pair of numbers. The first number is a Unix UTC timestamp (seconds since January 1, 1970); the second is the offset of the committer's timezone from UTC, in seconds.files: List of strings. All files modified, added, or removed by this changeset.file_dels: List of strings. Files removed by this changeset.node: String. The changeset identification hash, as a 40-character hexadecimal string.rev: Integer. The repository-local changeset revision number.tags: List of strings. Any tags associated with the changeset.
A few simple experiments will show us what to expect when we use these keywords; you can see the results below.
$hg log -r1 --template 'author: {author}\n'author: Bryan O'Sullivan <bos@serpentine.com>$hg log -r1 --template 'desc:\n{desc}\n'desc: added line to end of <<hello>> file. in addition, added a file with the helpful name (at least i hope that some might consider it so) of goodbye.$hg log -r1 --template 'files: {files}\n'files: goodbye hello$hg log -r1 --template 'file_adds: {file_adds}\n'file_adds: goodbye$hg log -r1 --template 'file_dels: {file_dels}\n'file_dels:$hg log -r1 --template 'node: {node}\n'node: 107e439be01c456e8e32f719558cb7ea693b60fd$hg log -r1 --template 'parents: {parents}\n'parents:$hg log -r1 --template 'rev: {rev}\n'rev: 1$hg log -r1 --template 'tags: {tags}\n'tags: mytag
As we noted above, the date keyword does not produce human-readable output, so we must treat it specially. This involves using a filter, about which more in the section called “Filtering keywords to change their results”.
$hg log -r1 --template 'date: {date}\n'date: 1241506546.00$hg log -r1 --template 'date: {date|isodate}\n'date: 2009-05-05 06:55 +0000
Escape sequences
Mercurial's templating engine recognises the most commonly
used escape sequences in strings. When it sees a backslash
(“\”) character, it looks at the
following character and substitutes the two characters with a
single replacement, as described below.
As indicated above, if you want the expansion of a template
to contain a literal “\”,
“{”, or
“{” character, you must escape
it.
Filtering keywords to change their results
Some of the results of template expansion are not
immediately easy to use. Mercurial lets you specify an optional
chain of filters to modify the result of
expanding a keyword. You have already seen a common filter,
isodate, in
action above, to make a date readable.
Below is a list of the most commonly used filters that Mercurial supports. While some filters can be applied to any text, others can only be used in specific circumstances. The name of each filter is followed first by an indication of where it can be used, then a description of its effect.
addbreaks: Any text. Add an XHTML “<br/>” tag before the end of every line except the last. For example, “foo\nbar” becomes “foo<br/>\nbar”.age:datekeyword. Render the age of the date, relative to the current time. Yields a string like “10 minutes”.basename: Any text, but most useful for thefileskeyword and its relatives. Treat the text as a path, and return the basename. For example, “foo/bar/baz” becomes “baz”.date:datekeyword. Render a date in a similar format to the Unixdatecommand, but with timezone included. Yields a string like “Mon Sep 04 15:13:13 2006 -0700”.domain: Any text, but most useful for theauthorkeyword. Finds the first string that looks like an email address, and extract just the domain component. For example, “Bryan O'Sullivan <bos@serpentine.com>” becomes “serpentine.com”.email: Any text, but most useful for theauthorkeyword. Extract the first string that looks like an email address. For example, “Bryan O'Sullivan <bos@serpentine.com>” becomes “bos@serpentine.com”.escape: Any text. Replace the special XML/XHTML characters “&”, “<” and “>” with XML entities.fill68: Any text. Wrap the text to fit in 68 columns. This is useful before you pass text through thetabindentfilter, and still want it to fit in an 80-column fixed-font window.firstline: Any text. Yield the first line of text, without any trailing newlines.hgdate:datekeyword. Render the date as a pair of readable numbers. Yields a string like “1157407993 25200”.isodate:datekeyword. Render the date as a text string in ISO 8601 format. Yields a string like “2006-09-04 15:13:13 -0700”.obfuscate: Any text, but most useful for theauthorkeyword. Yield the input text rendered as a sequence of XML entities. This helps to defeat some particularly stupid screen-scraping email harvesting spambots.person: Any text, but most useful for theauthorkeyword. Yield the text before an email address. For example, “Bryan O'Sullivan <bos@serpentine.com>” becomes “Bryan O'Sullivan”.rfc822date:datekeyword. Render a date using the same format used in email headers. Yields a string like “Mon, 04 Sep 2006 15:13:13 -0700”.short: Changeset hash. Yield the short form of a changeset hash, i.e. a 12-character hexadecimal string.shortdate:datekeyword. Render the year, month, and day of the date. Yields a string like “2006-09-04”.strip: Any text. Strip all leading and trailing whitespace from the string.tabindent: Any text. Yield the text, with every line except the first starting with a tab character.urlescape: Any text. Escape all characters that are considered “special” by URL parsers. For example,foo barbecomesfoo%20bar.user: Any text, but most useful for theauthorkeyword. Return the “user” portion of an email address. For example, “Bryan O'Sullivan <bos@serpentine.com>” becomes “bos”.
$hg log -r1 --template '{author}\n'Bryan O'Sullivan <bos@serpentine.com>$hg log -r1 --template '{author|domain}\n'serpentine.com$hg log -r1 --template '{author|email}\n'bos@serpentine.com$hg log -r1 --template '{author|obfuscate}\n' | cut -c-76Bryan O'Sulli$hg log -r1 --template '{author|person}\n'Bryan O'Sullivan$hg log -r1 --template '{author|user}\n'bos$hg log -r1 --template 'looks almost right, but actually garbage: {date}\n'looks almost right, but actually garbage: 1241506546.00$hg log -r1 --template '{date|age}\n'2 seconds$hg log -r1 --template '{date|date}\n'Tue May 05 06:55:46 2009 +0000$hg log -r1 --template '{date|hgdate}\n'1241506546 0$hg log -r1 --template '{date|isodate}\n'2009-05-05 06:55 +0000$hg log -r1 --template '{date|rfc822date}\n'Tue, 05 May 2009 06:55:46 +0000$hg log -r1 --template '{date|shortdate}\n'2009-05-05$hg log -r1 --template '{desc}\n' | cut -c-76added line to end of <<hello>> file. in addition, added a file with the helpful name (at least i hope that some m$hg log -r1 --template '{desc|addbreaks}\n' | cut -c-76added line to end of <<hello>> file.<br/> <br/> in addition, added a file with the helpful name (at least i hope that some m$hg log -r1 --template '{desc|escape}\n' | cut -c-76added line to end of <<hello>> file. in addition, added a file with the helpful name (at least i hope that some m$hg log -r1 --template '{desc|fill68}\n'added line to end of <<hello>> file. in addition, added a file with the helpful name (at least i hope that some might consider it so) of goodbye.$hg log -r1 --template '{desc|fill76}\n'added line to end of <<hello>> file. in addition, added a file with the helpful name (at least i hope that some might consider it so) of goodbye.$hg log -r1 --template '{desc|firstline}\n'added line to end of <<hello>> file.$hg log -r1 --template '{desc|strip}\n' | cut -c-76added line to end of <<hello>> file. in addition, added a file with the helpful name (at least i hope that some m$hg log -r1 --template '{desc|tabindent}\n' | expand | cut -c-76added line to end of <<hello>> file. in addition, added a file with the helpful name (at least i hope tha$hg log -r1 --template '{node}\n'107e439be01c456e8e32f719558cb7ea693b60fd$hg log -r1 --template '{node|short}\n'107e439be01c
![[Note]](/support/figs/note.png)
Combining filters
It is easy to combine filters to yield output in the form you would like. The following chain of filters tidies up a description, then makes sure that it fits cleanly into 68 columns, then indents it by a further 8 characters (at least on Unix-like systems, where a tab is conventionally 8 characters wide).
$hg log -r1 --template 'description:\n\t{desc|strip|fill68|tabindent}\n'description: added line to end of <<hello>> file. in addition, added a file with the helpful name (at least i hope that some might consider it so) of goodbye.
Note the use of “\t” (a
tab character) in the template to force the first line to be
indented; this is necessary since tabindent indents all
lines except the first.
Keep in mind that the order of filters in a chain is
significant. The first filter is applied to the result of the
keyword; the second to the result of the first filter; and so
on. For example, using fill68|tabindent
gives very different results from
tabindent|fill68.
From templates to styles
A command line template provides a quick and simple way to format some output. Templates can become verbose, though, and it's useful to be able to give a template a name. A style file is a template with a name, stored in a file.
More than that, using a style file unlocks the power of
Mercurial's templating engine in ways that are not possible
using the command line --template option.
The simplest of style files
Our simple style file contains just one line:
$echo 'changeset = "rev: {rev}\n"' > rev$hg log -l1 --style ./revrev: 3
This tells Mercurial, “if you're printing a changeset, use the text on the right as the template”.
Style file syntax
The syntax rules for a style file are simple.
If a line starts with either of the characters “
#” or “;”, the entire line is treated as a comment, and skipped as if empty.A line starts with a keyword. This must start with an alphabetic character or underscore, and can subsequently contain any alphanumeric character or underscore. (In regexp notation, a keyword must match
[A-Za-z_][A-Za-z0-9_]*.)The next element must be an “
=” character, which can be preceded or followed by an arbitrary amount of white space.If the rest of the line starts and ends with matching quote characters (either single or double quote), it is treated as a template body.
If the rest of the line does not start with a quote character, it is treated as the name of a file; the contents of this file will be read and used as a template body.
Style files by example
To illustrate how to write a style file, we will construct a few by example. Rather than provide a complete style file and walk through it, we'll mirror the usual process of developing a style file by starting with something very simple, and walking through a series of successively more complete examples.
Identifying mistakes in style files
If Mercurial encounters a problem in a style file you are working on, it prints a terse error message that, once you figure out what it means, is actually quite useful.
$cat broken.stylechangeset =
Notice that broken.style attempts to
define a changeset keyword, but forgets to
give any content for it. When instructed to use this style
file, Mercurial promptly complains.
$hg log -r1 --style broken.styleabort: broken.style:1: parse error
This error message looks intimidating, but it is not too hard to follow.
The first component is simply Mercurial's way of saying “I am giving up”.
___abort___: broken.style:1: parse error
Next comes the name of the style file that contains the error.
abort: ___broken.style___:1: parse error
Following the file name is the line number where the error was encountered.
abort: broken.style:___1___: parse error
Finally, a description of what went wrong.
abort: broken.style:1: ___parse error___
The description of the problem is not always clear (as in this case), but even when it is cryptic, it is almost always trivial to visually inspect the offending line in the style file and see what is wrong.
Uniquely identifying a repository
If you would like to be able to identify a Mercurial repository “fairly uniquely” using a short string as an identifier, you can use the first revision in the repository.
$hg log -r0 --template '{node}'189e736977c29ea3835dfc7e332794a24f479c51
This is likely to be unique, and so it is useful in many cases. There are a few caveats.
Listing files on multiple lines
Suppose we want to list the files changed by a changeset, one per line, with a little indentation before each file name.
$cat > multiline << EOF>changeset = "Changed in {node|short}:\n{files}">file = " {file}\n">EOF$hg log --style multilineChanged in ae47487e0fed: .bashrc .hgrc test.c
Mimicking Subversion's output
Let's try to emulate the default output format used by another revision control tool, Subversion.
$svn log -r9653------------------------------------------------------------------------ r9653 | sean.hefty | 2006-09-27 14:39:55 -0700 (Wed, 27 Sep 2006) | 5 lines On reporting a route error, also include the status for the error, rather than indicating a status of 0 when an error has occurred. Signed-off-by: Sean Hefty <sean.hefty@intel.com> ------------------------------------------------------------------------
Since Subversion's output style is fairly simple, it is easy to copy-and-paste a hunk of its output into a file, and replace the text produced above by Subversion with the template values we'd like to see expanded.
$cat svn.templater{rev} | {author|user} | {date|isodate} ({date|rfc822date}) {desc|strip|fill76} ------------------------------------------------------------------------
There are a few small ways in which this template deviates from the output produced by Subversion.
Subversion prints a “readable” date (the “
Wed, 27 Sep 2006” in the example output above) in parentheses. Mercurial's templating engine does not provide a way to display a date in this format without also printing the time and time zone.We emulate Subversion's printing of “separator” lines full of “
-” characters by ending the template with such a line. We use the templating engine'sheaderkeyword to print a separator line as the first line of output (see below), thus achieving similar output to Subversion.Subversion's output includes a count in the header of the number of lines in the commit message. We cannot replicate this in Mercurial; the templating engine does not currently provide a filter that counts the number of lines the template generates.
It took me no more than a minute or two of work to replace literal text from an example of Subversion's output with some keywords and filters to give the template above. The style file simply refers to the template.
$cat svn.styleheader = '------------------------------------------------------------------------\n\n' changeset = svn.template
We could have included the text of the template file
directly in the style file by enclosing it in quotes and
replacing the newlines with
“\n” sequences, but it would
have made the style file too difficult to read. Readability
is a good guide when you're trying to decide whether some text
belongs in a style file, or in a template file that the style
file points to. If the style file will look too big or
cluttered if you insert a literal piece of text, drop it into
a template instead.
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