diff mercurial/helptext/scripting.txt @ 43632:2e017696181f

help: create packages for the help text

These files need to be loaded as resources with PyOxidizer, instead of using
filesystem representations.  AFAICT, the resource loading mechanisms only work
for the named package given to it, and can't reach into a subdirectory.

While here, the `help` directory is renamed to `helptext`.  Without this, trying
to load external help text crashed in mercurial/help.py when importing `.i18n`,
saying there's no `mercurial.help.i18n` module.

Differential Revision: https://phab.mercurial-scm.org/D7376

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mercurial/helptext/scripting.txt	Wed Nov 13 21:52:25 2019 -0500
@@ -0,0 +1,202 @@
+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 familiar 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://www.mercurial-scm.org/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).
+
+    Explicitly 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.
+
+Command-line Flags
+==================
+
+Mercurial's default command-line parser is designed for humans, and is not
+robust against malicious input. For instance, you can start a debugger by
+passing ``--debugger`` as an option value::
+
+    $ REV=--debugger sh -c 'hg log -r "$REV"'
+
+This happens because several command-line flags need to be scanned without
+using a concrete command table, which may be modified while loading repository
+settings and extensions.
+
+Since Mercurial 4.4.2, the parsing of such flags may be restricted by setting
+``HGPLAIN=+strictflags``. When this feature is enabled, all early options
+(e.g. ``-R/--repository``, ``--cwd``, ``--config``) must be specified first
+amongst the other global options, and cannot be injected to an arbitrary
+location::
+
+    $ HGPLAIN=+strictflags hg -R "$REPO" log -r "$REV"
+
+In earlier Mercurial versions where ``+strictflags`` isn't available, you
+can mitigate the issue by concatenating an option value with its flag::
+
+    $ hg log -r"$REV" --keyword="$KEYWORD"
+
+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 ``cbor``, ``json``,
+and ``xml``, which provide CBOR, JSON, and XML output, respectively.
+These are useful for producing output that is machine readable as-is.
+
+(Mercurial 5.0 is required for CBOR style.)
+
+.. 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.