git/Documentation/git-sh-setup.txt
Junio C Hamano c3e2d18996 setup_reflog_action: document the rules for using GIT_REFLOG_ACTION
The set_reflog_action helper (in git-sh-setup) is designed to be
used once at the very top of a program, like this in "git am", for
example:

	set_reflog_action am

The helper function sets the given string to GIT_REFLOG_ACTION only
when GIT_REFLOG_ACTION is not yet set.  Thanks to this, "git am",
when run as the top-level program, will use "am" in GIT_REFLOG_ACTION
and the reflog entries made by whatever it does will record the
updates of refs done by "am".

Because of the conditional assignment, when "git am" is run as a
subprogram (i.e. an implementation detail) of "git rebase" that
already sets GIT_REFLOG_ACTION to its own name, the call in "git am"
to the helper function at the beginning will *not* have any effect.

So "git rebase" can do this:

	set_reflog_action rebase
	... do its own preparation, like checking out "onto" commit
        ... decide to do "format-patch" to "am" pipeline
        	git format-patch --stdout >mbox
		git am mbox

and the reflog entries made inside "git am" invocation will say
"rebase", not "am".

Calls to "git" commands that update refs would use GIT_REFLOG_ACTION
to record who did that update.  Most such calls in scripted Porcelains
do not define custom reflog message and rely on GIT_REFLOG_ACTION to
contain its (or its caller's, when it is called as a subprogram) name.

If a scripted Porcelain wants to record a custom reflog message for
a single invocation of "git" command (e.g. when "git rebase" uses
"git checkout" to detach HEAD at the commit a series is to be
replayed on), it needs to set GIT_REFLOG_ACTION to the custom
message and export it while calling the "git" command, but such an
assignment must be restricted to that single "git" invocation and
should not be left behind to affect later codepath.

Document the rules to avoid future confusion.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2013-06-19 10:54:00 -07:00

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git-sh-setup(1)
===============
NAME
----
git-sh-setup - Common Git shell script setup code
SYNOPSIS
--------
[verse]
'. "$(git --exec-path)/git-sh-setup"'
DESCRIPTION
-----------
This is not a command the end user would want to run. Ever.
This documentation is meant for people who are studying the
Porcelain-ish scripts and/or are writing new ones.
The 'git sh-setup' scriptlet is designed to be sourced (using
`.`) by other shell scripts to set up some variables pointing at
the normal Git directories and a few helper shell functions.
Before sourcing it, your script should set up a few variables;
`USAGE` (and `LONG_USAGE`, if any) is used to define message
given by `usage()` shell function. `SUBDIRECTORY_OK` can be set
if the script can run from a subdirectory of the working tree
(some commands do not).
The scriptlet sets `GIT_DIR` and `GIT_OBJECT_DIRECTORY` shell
variables, but does *not* export them to the environment.
FUNCTIONS
---------
die::
exit after emitting the supplied error message to the
standard error stream.
usage::
die with the usage message.
set_reflog_action::
Set GIT_REFLOG_ACTION environment to a given string (typically
the name of the program) unless it is already set. Whenever
the script runs a `git` command that updates refs, a reflog
entry is created using the value of this string to leave the
record of what command updated the ref.
git_editor::
runs an editor of user's choice (GIT_EDITOR, core.editor, VISUAL or
EDITOR) on a given file, but error out if no editor is specified
and the terminal is dumb.
is_bare_repository::
outputs `true` or `false` to the standard output stream
to indicate if the repository is a bare repository
(i.e. without an associated working tree).
cd_to_toplevel::
runs chdir to the toplevel of the working tree.
require_work_tree::
checks if the current directory is within the working tree
of the repository, and otherwise dies.
require_work_tree_exists::
checks if the working tree associated with the repository
exists, and otherwise dies. Often done before calling
cd_to_toplevel, which is impossible to do if there is no
working tree.
require_clean_work_tree <action> [<hint>]::
checks that the working tree and index associated with the
repository have no uncommitted changes to tracked files.
Otherwise it emits an error message of the form `Cannot
<action>: <reason>. <hint>`, and dies. Example:
+
----------------
require_clean_work_tree rebase "Please commit or stash them."
----------------
get_author_ident_from_commit::
outputs code for use with eval to set the GIT_AUTHOR_NAME,
GIT_AUTHOR_EMAIL and GIT_AUTHOR_DATE variables for a given commit.
GIT
---
Part of the linkgit:git[1] suite