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git/Documentation/git-patch-id.txt
Junio C Hamano 33e8fc8740 usage: do not insist that standard input must come from a file
The synopsys text and the usage string of subcommands that read list
of things from the standard input are often shown like this:

	git gostak [--distim] < <list-of-doshes>

This is problematic in a number of ways:

 * The way to use these commands is more often to feed them the
   output from another command, not feed them from a file.

 * Manual pages outside Git, commands that operate on the data read
   from the standard input, e.g "sort", "grep", "sed", etc., are not
   described with such a "< redirection-from-file" in their synopsys
   text.  Our doing so introduces inconsistency.

 * We do not insist on where the output should go, by saying

	git gostak [--distim] < <list-of-doshes> > <output>

 * As it is our convention to enclose placeholders inside <braket>,
   the redirection operator followed by a placeholder filename
   becomes very hard to read, both in the documentation and in the
   help text.

Let's clean them all up, after making sure that the documentation
clearly describes the modes that take information from the standard
input and what kind of things are expected on the input.

[jc: stole example for fmt-merge-msg from Jonathan]

Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2015-10-16 15:27:52 -07:00

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git-patch-id(1)
===============
NAME
----
git-patch-id - Compute unique ID for a patch
SYNOPSIS
--------
[verse]
'git patch-id' [--stable | --unstable]
DESCRIPTION
-----------
Read a patch from the standard input and compute the patch ID for it.
A "patch ID" is nothing but a sum of SHA-1 of the file diffs associated with a
patch, with whitespace and line numbers ignored. As such, it's "reasonably
stable", but at the same time also reasonably unique, i.e., two patches that
have the same "patch ID" are almost guaranteed to be the same thing.
IOW, you can use this thing to look for likely duplicate commits.
When dealing with 'git diff-tree' output, it takes advantage of
the fact that the patch is prefixed with the object name of the
commit, and outputs two 40-byte hexadecimal strings. The first
string is the patch ID, and the second string is the commit ID.
This can be used to make a mapping from patch ID to commit ID.
OPTIONS
-------
--stable::
Use a "stable" sum of hashes as the patch ID. With this option:
- Reordering file diffs that make up a patch does not affect the ID.
In particular, two patches produced by comparing the same two trees
with two different settings for "-O<orderfile>" result in the same
patch ID signature, thereby allowing the computed result to be used
as a key to index some meta-information about the change between
the two trees;
- Result is different from the value produced by git 1.9 and older
or produced when an "unstable" hash (see --unstable below) is
configured - even when used on a diff output taken without any use
of "-O<orderfile>", thereby making existing databases storing such
"unstable" or historical patch-ids unusable.
This is the default if patchid.stable is set to true.
--unstable::
Use an "unstable" hash as the patch ID. With this option,
the result produced is compatible with the patch-id value produced
by git 1.9 and older. Users with pre-existing databases storing
patch-ids produced by git 1.9 and older (who do not deal with reordered
patches) may want to use this option.
This is the default.
<patch>::
The diff to create the ID of.
GIT
---
Part of the linkgit:git[1] suite