[PATCH STABLE v2] help: scripting help topic
Gregory Szorc
gregory.szorc at gmail.com
Thu Jul 30 03:53:16 UTC 2015
# HG changeset patch
# User Gregory Szorc <gregory.szorc at gmail.com>
# Date 1437264628 25200
# Sat Jul 18 17:10:28 2015 -0700
# Branch stable
# Node ID 625913c1ab0c79f8a584581913bf99d281cd005b
# Parent 85785cd3b69f09f2e6ffa78dac75d68d08e400bd
help: scripting help topic
There are a lot of non-human consumers of Mercurial. And the challenges
and considerations for machines consuming Mercurial is significantly
different from what humans face.
I think there are enough special considerations around how machines
consume Mercurial that a dedicated help topic is warranted. I concede
the audience for this topic is probably small compared to the general
audience. However, lots of normal Mercurial users do things like create
one-off shell scripts for common workflows that I think this is useful
enough to be in the install (as opposed to, say, a wiki page - which
most users will likely never find).
This text is by no means perfect. But you have to start somewhere. I
think I did cover the important parts, though.
diff --git a/mercurial/help.py b/mercurial/help.py
--- a/mercurial/help.py
+++ b/mercurial/help.py
@@ -165,8 +165,10 @@ helptable = sorted([
(["glossary"], _("Glossary"), loaddoc('glossary')),
(["hgignore", "ignore"], _("Syntax for Mercurial Ignore Files"),
loaddoc('hgignore')),
(["phases"], _("Working with Phases"), loaddoc('phases')),
+ (['scripting'], _('Using Mercurial from scripts and automation'),
+ loaddoc('scripting')),
])
# Map topics to lists of callable taking the current topic help and
# returning the updated version
diff --git a/mercurial/help/scripting.txt b/mercurial/help/scripting.txt
new file mode 100644
--- /dev/null
+++ b/mercurial/help/scripting.txt
@@ -0,0 +1,174 @@
+It is common for machines (as opposed to humans) to consume Mercurial.
+This help topic describes some of the considerations for interfacing
+machines with Mercurial.
+
+Choosing an Interface
+=====================
+
+Machines have a choice of several methods to interface with Mercurial.
+These include:
+
+- Executing the ``hg`` process
+- Querying a HTTP server
+- Calling out to a command server
+
+Executing ``hg`` processes is very similar to how humans interact with
+Mercurial in the shell. It should already be familar to you.
+
+:hg:`serve` can be used to start a server. By default, this will start
+a "hgweb" HTTP server. This HTTP server has support for machine-readable
+output, such as JSON. For more, see :hg:`help hgweb`.
+
+:hg:`serve` can also start a "command server." Clients can connect
+to this server and issue Mercurial commands over a special protocol.
+For more details on the command server, including links to client
+libraries, see https://mercurial.selenic.com/wiki/CommandServer.
+
+:hg:`serve` based interfaces (the hgweb and command servers) have the
+advantage over simple ``hg`` process invocations in that they are
+likely more efficient. This is because there is significant overhead
+to spawn new Python processes.
+
+.. tip::
+
+ If you need to invoke several ``hg`` processes in short order and/or
+ performance is important to you, use of a server-based interface
+ is highly recommended.
+
+Environment Variables
+=====================
+
+As documented in :hg:`help environment`, various environment variables
+influence the operation of Mercurial. The following are particularly
+relevant for machines consuming Mercurial:
+
+HGPLAIN
+ If not set, Mercurial's output could be influenced by configuration
+ settings that impact its encoding, verbose mode, localization, etc.
+
+ It is highly recommended for machines to set this variable when
+ invoking ``hg`` processes.
+
+HGENCODING
+ If not set, the locale used by Mercurial will be detected from the
+ environment. If the determined locale does not support display of
+ certain characters, Mercurial may render these character sequences
+ incorrectly (often by using "?" as a placeholder for invalid
+ characters in the current locale).
+
+ Explcitly setting this environment variable is a good practice to
+ guarantee consistent results. "utf-8" is a good choice on UNIX-like
+ environments.
+
+HGRCPATH
+ If not set, Mercurial will inherit config options from config files
+ using the process described in :hg:`help config`. This includes
+ inheriting user or system-wide config files.
+
+ When utmost control over the Mercurial configuration is desired, the
+ value of ``HGRCPATH`` can be set to an explicit file with known good
+ configs. In rare cases, the value can be set to an empty file or the
+ null device (often ``/dev/null``) to bypass loading of any user or
+ system config files. Note that these approaches can have unintended
+ consequences, as the user and system config files often define things
+ like the username and extensions that may be required to interface
+ with a repository.
+
+Consuming Command Output
+========================
+
+It is common for machines to need to parse the output of Mercurial
+commands for relevant data. This section describes the various
+techniques for doing so.
+
+Parsing Raw Command Output
+--------------------------
+
+Likely the simplest and most effective solution for consuming command
+output is to simply invoke ``hg`` commands as you would as a user and
+parse their output.
+
+The output of many commands can easily be parsed with tools like
+``grep``, ``sed``, and ``awk``.
+
+A potential downside with parsing command output is that the output
+of commands can change when Mercurial is upgraded. While Mercurial
+does generally strive for strong backwards compatibility, command
+output does occasionally change. Having tests for your automated
+interactions with ``hg`` commands is generally recommended, but is
+even more important when raw command output parsing is involved.
+
+Using Templates to Control Output
+---------------------------------
+
+Many ``hg`` commands support templatized output via the
+``-T/--template`` argument. For more, see :hg:`help templates`.
+
+Templates are useful for explicitly controlling output so that
+you get exactly the data you want formatted how you want it. For
+example, ``log -T {node}\n`` can be used to print a newline
+delimited list of changeset nodes instead of a human-tailored
+output containing authors, dates, descriptions, etc.
+
+.. tip::
+
+ If parsing raw command output is too complicated, consider
+ using templates to make your life easier.
+
+The ``-T/--template`` argument allows specifying pre-defined styles.
+Mercurial ships with the machine-readable styles ``json`` and ``xml``,
+which provide JSON and XML output, respectively. These are useful for
+producing output that is machine readable as-is.
+
+.. important::
+
+ The ``json`` and ``xml`` styles are considered experimental. While
+ they may be attractive to use for easily obtaining machine-readable
+ output, their behavior may change in subsequent versions.
+
+ These styles may also exhibit unexpected results when dealing with
+ certain encodings. Mercurial treats things like filenames as a
+ series of bytes and normalizing certain byte sequences to JSON
+ or XML with certain encoding settings can lead to surprises.
+
+Command Server Output
+---------------------
+
+If using the command server to interact with Mercurial, you are likely
+using an existing library/API that abstracts implementation details of
+the command server. If so, this interface layer may perform parsing for
+you, saving you the work of implementing it yourself.
+
+Output Verbosity
+----------------
+
+Commands often have varying output verbosity, even when machine
+readable styles are being used (e.g. ``-T json``). Adding
+``-v/--verbose`` and ``--debug`` to the command's arguments can
+increase the amount of data exposed by Mercurial.
+
+An alternate way to get the data you need is by explicitly specifying
+a template.
+
+Other Topics
+============
+
+revsets
+ Revisions sets is a functional query language for selecting a set
+ of revisions. Think of it as SQL for Mercurial repositories. Revsets
+ are useful for querying repositories for specific data.
+
+ See :hg:`help revsets` for more.
+
+share extension
+ The ``share`` extension provides functionality for sharing
+ repository data across several working copies. It can even
+ automatically "pool" storage for logically related repositories when
+ cloning.
+
+ Configuring the ``share`` extension can lead to significant resource
+ utilization reduction, particularly around disk space and the
+ network. This is especially true for continuous integration (CI)
+ environments.
+
+ See :hg:`help -e share` for more.
diff --git a/tests/test-globalopts.t b/tests/test-globalopts.t
--- a/tests/test-globalopts.t
+++ b/tests/test-globalopts.t
@@ -354,8 +354,9 @@ Testing -h/--help:
patterns File Name Patterns
phases Working with Phases
revisions Specifying Single Revisions
revsets Specifying Revision Sets
+ scripting Using Mercurial from scripts and automation
subrepos Subrepositories
templating Template Usage
urls URL Paths
@@ -435,8 +436,9 @@ Testing -h/--help:
patterns File Name Patterns
phases Working with Phases
revisions Specifying Single Revisions
revsets Specifying Revision Sets
+ scripting Using Mercurial from scripts and automation
subrepos Subrepositories
templating Template Usage
urls URL Paths
diff --git a/tests/test-help.t b/tests/test-help.t
--- a/tests/test-help.t
+++ b/tests/test-help.t
@@ -116,8 +116,9 @@ Short help:
patterns File Name Patterns
phases Working with Phases
revisions Specifying Single Revisions
revsets Specifying Revision Sets
+ scripting Using Mercurial from scripts and automation
subrepos Subrepositories
templating Template Usage
urls URL Paths
@@ -191,8 +192,9 @@ Short help:
patterns File Name Patterns
phases Working with Phases
revisions Specifying Single Revisions
revsets Specifying Revision Sets
+ scripting Using Mercurial from scripts and automation
subrepos Subrepositories
templating Template Usage
urls URL Paths
@@ -739,8 +741,9 @@ Test that default list of commands omits
patterns File Name Patterns
phases Working with Phases
revisions Specifying Single Revisions
revsets Specifying Revision Sets
+ scripting Using Mercurial from scripts and automation
subrepos Subrepositories
templating Template Usage
urls URL Paths
@@ -1405,8 +1408,15 @@ Dish up an empty repo; serve it cold.
</td><td>
Specifying Revision Sets
</td></tr>
<tr><td>
+ <a href="/help/scripting">
+ scripting
+ </a>
+ </td><td>
+ Using Mercurial from scripts and automation
+ </td></tr>
+ <tr><td>
<a href="/help/subrepos">
subrepos
</a>
</td><td>
diff --git a/tests/test-hgweb-json.t b/tests/test-hgweb-json.t
--- a/tests/test-hgweb-json.t
+++ b/tests/test-hgweb-json.t
@@ -1085,8 +1085,12 @@ help/ shows help topics
"summary": "Specifying Revision Sets",
"topic": "revsets"
},
{
+ "summary": "Using Mercurial from scripts and automation",
+ "topic": "scripting"
+ },
+ {
"summary": "Subrepositories",
"topic": "subrepos"
},
{
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