git-rev-parse

git rev-parse [ --option ] <args>...

Many Git porcelainish commands take mixture of flags (i.e. parameters that begin with a dash -) and parameters meant for the underlying git rev-list command they use internally and flags and parameters for the other commands they use downstream of git rev-list. This command is used to distinguish between them.

A revision parameter <rev> typically, but not necessarily, names a commit object. It uses what is called an extended SHA-1 syntax. Here are various ways to spell object names. The ones listed near the end of this list name trees and blobs contained in a commit.

<sha1>, e.g. dae86e1950b1277e545cee180551750029cfe735, dae86e

<describeOutput>, e.g. v1.7.4.2-679-g3bee7fb

<refname>, e.g. master, heads/master, refs/heads/master

@

<refname>@{<date>}, e.g. master@{yesterday}, HEAD@{5 minutes ago}

<refname>@{<n>}, e.g. master@{1}

@{<n>}, e.g. @{1}

@{-<n>}, e.g. @{-1}

<branchname>@{upstream}, e.g. master@{upstream}, @{u}

<rev>^, e.g. HEAD^, v1.5.1^0

<rev>~<n>, e.g. master~3

<rev>^{<type>}, e.g. v0.99.8^{commit}

<rev>^{}, e.g. v0.99.8^{}

<rev>^{/<text>}, e.g. HEAD^{/fix nasty bug}

:/<text>, e.g. :/fix nasty bug

<rev>:<path>, e.g. HEAD:README, :README, master:./README

:<n>:<path>, e.g. :0:README, :README

Here is an illustration, by Jon Loeliger. Both commit nodes B and C are parents of commit node A. Parent commits are ordered left-to-right.

G   H   I   J
 \ /     \ /
  D   E   F
   \  |  / \
    \ | /   |
     \|/    |
      B     C
       \   /
        \ /
         A

A =      = A^0
B = A^   = A^1     = A~1
C = A^2  = A^2
D = A^^  = A^1^1   = A~2
E = B^2  = A^^2
F = B^3  = A^^3
G = A^^^ = A^1^1^1 = A~3
H = D^2  = B^^2    = A^^^2  = A~2^2
I = F^   = B^3^    = A^^3^
J = F^2  = B^3^2   = A^^3^2

History traversing commands such as git log operate on a set of commits, not just a single commit. To these commands, specifying a single revision with the notation described in the previous section means the set of commits reachable from that commit, following the commit ancestry chain.

To exclude commits reachable from a commit, a prefix ^ notation is used. E.g. ^r1 r2 means commits reachable from r2 but exclude the ones reachable from r1.

This set operation appears so often that there is a shorthand for it. When you have two commits r1 and r2 (named according to the syntax explained in SPECIFYING REVISIONS above), you can ask for commits that are reachable from r2 excluding those that are reachable from r1 by ^r1 r2 and it can be written as r1..r2.

A similar notation r1...r2 is called symmetric difference of r1 and r2 and is defined as r1 r2 --not $(git merge-base --all r1 r2). It is the set of commits that are reachable from either one of r1 or r2 but not from both.

In these two shorthands, you can omit one end and let it default to HEAD. For example, origin.. is a shorthand for origin..HEAD and asks "What did I do since I forked from the origin branch?" Similarly, ..origin is a shorthand for HEAD..origin and asks "What did the origin do since I forked from them?" Note that .. would mean HEAD..HEAD which is an empty range that is both reachable and unreachable from HEAD.

Two other shorthands for naming a set that is formed by a commit and its parent commits exist. The r1^@ notation means all parents of r1. r1^! includes commit r1 but excludes all of its parents.

To summarize:

<rev>

^<rev>

<rev1>..<rev2>

<rev1>...<rev2>

<rev>^@, e.g. HEAD^@

<rev>^!, e.g. HEAD^!

Here are a handful of examples:

D                G H D
D F              G H I J D F
^G D             H D
^D B             E I J F B
B..C             C
B...C            G H D E B C
^D B C           E I J F B C
C                I J F C
C^@              I J F
C^!              C
F^! D            G H D F

In --parseopt mode, git rev-parse helps massaging options to bring to shell scripts the same facilities C builtins have. It works as an option normalizer (e.g. splits single switches aggregate values), a bit like getopt(1) does.

It takes on the standard input the specification of the options to parse and understand, and echoes on the standard output a string suitable for sh(1) eval to replace the arguments with normalized ones. In case of error, it outputs usage on the standard error stream, and exits with code 129.

Note: Make sure you quote the result when passing it to eval. See below for an example.

<opt_spec><flags>* SP+ help LF

OPTS_SPEC="\
some-command [options] <args>...
some-command does foo and bar!
--
h,help    show the help
foo       some nifty option --foo
bar=      some cool option --bar with an argument
  An option group Header
C?        option C with an optional argument"
eval "$(echo "$OPTS_SPEC" | git rev-parse --parseopt -- "$@" || echo exit $?)"

In --sq-quote mode, git rev-parse echoes on the standard output a single line suitable for sh(1) eval. This line is made by normalizing the arguments following --sq-quote. Nothing other than quoting the arguments is done.

If you want command input to still be interpreted as usual by git rev-parse before the output is shell quoted, see the --sq option.

$ cat >your-git-script.sh <<\EOF
#!/bin/sh
args=$(git rev-parse --sq-quote "$@")   # quote user-supplied arguments
command="git frotz -n24 $args"          # and use it inside a handcrafted
                                        # command line
eval "$command"
EOF
$ sh your-git-script.sh "a b'c"

Part of the git(1) suite