Document git-filter-branch

This moves the documentation in git-filter-branch.sh to its own
man page, with a few touch ups (incorporating comments by Frank
Lichtenheld).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 3 insertions, 184 deletions

diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index 3772951..22fb5bf 100644
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -4,190 +4,9 @@
 # Copyright (c) Petr Baudis, 2006
 # Minimal changes to "port" it to core-git (c) Johannes Schindelin, 2007
 #
-# Lets you rewrite GIT revision history by creating a new branch from
-# your current branch by applying custom filters on each revision.
-# Those filters can modify each tree (e.g. removing a file or running
-# a perl rewrite on all files) or information about each commit.
-# Otherwise, all information (including original commit times or merge
-# information) will be preserved.
-#
-# The command takes the new branch name as a mandatory argument and
-# the filters as optional arguments. If you specify no filters, the
-# commits will be recommitted without any changes, which would normally
-# have no effect and result with the new branch pointing to the same
-# branch as your current branch. (Nevertheless, this may be useful in
-# the future for compensating for some Git bugs or such, therefore
-# such a usage is permitted.)
-#
-# WARNING! The rewritten history will have different ids for all the
-# objects and will not converge with the original branch. You will not
-# be able to easily push and distribute the rewritten branch. Please do
-# not use this command if you do not know the full implications, and
-# avoid using it anyway - do not do what a simple single commit on top
-# of the current version would fix.
-#
-# Always verify that the rewritten version is correct before disposing
-# the original branch.
-#
-# Note that since this operation is extensively I/O expensive, it might
-# be a good idea to do it off-disk, e.g. on tmpfs. Reportedly the speedup
-# is very noticeable.
-#
-# OPTIONS
-# -------
-# -d TEMPDIR:: The path to the temporary tree used for rewriting
-#	When applying a tree filter, the command needs to temporary
-#	checkout the tree to some directory, which may consume
-#	considerable space in case of large projects. By default it
-#	does this in the '.git-rewrite/' directory but you can override
-#	that choice by this parameter.
-#
-# Filters
-# ~~~~~~~
-# The filters are applied in the order as listed below. The COMMAND
-# argument is always evaluated in shell using the 'eval' command.
-# The $GIT_COMMIT environment variable is permanently set to contain
-# the id of the commit being rewritten. The author/committer environment
-# variables are set before the first filter is run.
-#
-# A 'map' function is available that takes an "original sha1 id" argument
-# and outputs a "rewritten sha1 id" if the commit has been already
-# rewritten, fails otherwise; the 'map' function can return several
-# ids on separate lines if your commit filter emitted multiple commits
-# (see below).
-#
-# --env-filter COMMAND:: The filter for modifying environment
-#	This is the filter for modifying the environment in which
-#	the commit will be performed. Specifically, you might want
-#	to rewrite the author/committer name/email/time environment
-#	variables (see `git-commit` for details). Do not forget to
-#	re-export the variables.
-#
-# --tree-filter COMMAND:: The filter for rewriting tree (and its contents)
-#	This is the filter for rewriting the tree and its contents.
-#	The COMMAND argument is evaluated in shell with the working
-#	directory set to the root of the checked out tree. The new tree
-#	is then used as-is (new files are auto-added, disappeared files
-#	are auto-removed - .gitignore files nor any other ignore rules
-#	HAVE NO EFFECT!).
-#
-# --index-filter COMMAND:: The filter for rewriting index
-#	This is the filter for rewriting the Git's directory index.
-#	It is similar to the tree filter but does not check out the
-#	tree, which makes it much faster. However, you must use the
-#	lowlevel Git index manipulation commands to do your work.
-#
-# --parent-filter COMMAND:: The filter for rewriting parents
-#	This is the filter for rewriting the commit's parent list.
-#	It will receive the parent string on stdin and shall output
-#	the new parent string on stdout. The parent string is in
-#	format accepted by `git commit-tree`: empty for initial
-#	commit, "-p parent" for a normal commit and "-p parent1
-#	-p parent2 -p parent3 ..." for a merge commit.
-#
-# --msg-filter COMMAND:: The filter for rewriting commit message
-#	This is the filter for rewriting the commit messages.
-#	The COMMAND argument is evaluated in shell with the original
-#	commit message on standard input; its standard output is
-#	is used as the new commit message.
-#
-# --commit-filter COMMAND:: The filter for performing the commit
-#	If this filter is passed, it will be called instead of the
-#	`git commit-tree` command, with those arguments:
-#
-#		TREE_ID [-p PARENT_COMMIT_ID]...
-#
-#	and the log message on stdin. The commit id is expected on
-#	stdout. As a special extension, the commit filter may emit
-#	multiple commit ids; in that case, all of them will be used
-#	as parents instead of the original commit in further commits.
-#
-# --tag-name-filter COMMAND:: The filter for rewriting tag names.
-#	If this filter is passed, it will be called for every tag ref
-#	that points to a rewritten object (or to a tag object which
-#	points to a rewritten object). The original tag name is passed
-#	via standard input, and the new tag name is expected on standard
-#	output.
-#
-#	The original tags are not deleted, but can be overwritten;
-#	use "--tag-name-filter=cat" to simply update the tags. In this
-#	case, be very careful and make sure you have the old tags
-#	backed up in case the conversion has run afoul.
-#
-#	Note that there is currently no support for proper rewriting of
-#	tag objects; in layman terms, if the tag has a message or signature
-#	attached, the rewritten tag won't have it. Sorry. (It is by
-#	definition impossible to preserve signatures at any rate, though.)
-#
-# --subdirectory-filter DIRECTORY:: Only regard the history, as seen by
-#	the given subdirectory. The result will contain that directory as
-#	its project root.
-#
-# EXAMPLE USAGE
-# -------------
-# Suppose you want to remove a file (containing confidential information
-# or copyright violation) from all commits:
-#
-#	git-filter-branch --tree-filter 'rm filename' newbranch
-#
-# A significantly faster version:
-#
-#	git-filter-branch --index-filter 'git update-index --remove filename' newbranch
-#
-# Now, you will get the rewritten history saved in the branch 'newbranch'
-# (your current branch is left untouched).
-#
-# To "etch-graft" a commit to the revision history (set a commit to be
-# the parent of the current initial commit and propagate that):
-#
-#	git-filter-branch --parent-filter sed\ 's/^$/-p graftcommitid/' newbranch
-#
-# (if the parent string is empty - therefore we are dealing with the
-# initial commit - add graftcommit as a parent). Note that this assumes
-# history with a single root (that is, no git-merge without common ancestors
-# happened). If this is not the case, use:
-#
-#	git-filter-branch --parent-filter 'cat; [ "$GIT_COMMIT" = "COMMIT" ] && echo "-p GRAFTCOMMIT"' newbranch
-#
-# To remove commits authored by "Darl McBribe" from the history:
-#
-#	git-filter-branch --commit-filter 'if [ "$GIT_AUTHOR_NAME" = "Darl McBribe" ]; then shift; while [ -n "$1" ]; do shift; echo "$1"; shift; done; else git commit-tree "$@"; fi' newbranch
-#
-# (the shift magic first throws away the tree id and then the -p
-# parameters). Note that this handles merges properly! In case Darl
-# committed a merge between P1 and P2, it will be propagated properly
-# and all children of the merge will become merge commits with P1,P2
-# as their parents instead of the merge commit.
-#
-# To restrict rewriting to only part of the history, specify a revision
-# range in addition to the new branch name. The new branch name will
-# point to the top-most revision that a 'git rev-list' of this range
-# will print.
-#
-# Consider this history:
-#
-#	     D--E--F--G--H
-#	    /     /
-#	A--B-----C
-#
-# To rewrite commits D,E,F,G,H, use:
-#
-#	git-filter-branch ... new-H C..H
-#
-# To rewrite commits E,F,G,H, use one of these:
-#
-#	git-filter-branch ... new-H C..H --not D
-#	git-filter-branch ... new-H D..H --not C
-#
-# To move the whole tree into a subdirectory, or remove it from there:
-#
-# git-filter-branch --index-filter \
-#	'git ls-files -s | sed "s-\t-&newsubdir/-" |
-#		GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
-#			git update-index --index-info &&
-#	 mv $GIT_INDEX_FILE.new $GIT_INDEX_FILE' directorymoved
-
-# Testsuite: TODO
+# Lets you rewrite the revision history of the current branch, creating
+# a new branch. You can specify a number of filters to modify the commits,
+# files and trees.
 
 set -e