Compute unique ID for a patch


gitpatch -id [ --stable | --unstable]


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 "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 gitdiff -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 .


--stable Use a "stable" sum of hashes as the patch ID . With this option:

'-04' '+03' .sp -1

2.3 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;
'-04' '+03' .sp -1

2.3 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 .
.RS 4
This is the default if patchid .stable is set to true . .RE

--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 .
.RS 4
This is the default . .RE


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