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What does git rev-parse do?
I have read the man page but it raised more questions than answers. Things like:
Pick out and massage parameters
Massage? What does that mean?
I'm using as a resolver (to SHA1) of revision specifiers, like
git rev-parse HEAD^ or
git rev-parse origin/master Is this the command’s purpose? If not, is even correct to use it to achieve this?
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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.
git rev-parse --show-toplevel gets you the repo root dir directly.
The git status command displays the state of the working directory and the staging area. It lets you see which changes have been staged, which haven't, and which files aren't being tracked by Git. Status output does not show you any information regarding the committed project history.
When working with Git, only one branch can be checked out at a time - and this is what's called the "HEAD" branch. Often, this is also referred to as the "active" or "current" branch. Git makes note of this current branch in a file located inside the Git repository, in .
git rev-parse is an ancillary plumbing command primarily used for manipulation.
One common usage of git rev-parse is to print the SHA1 hashes given a revision specifier. In addition, it has various options to format this output such as --short for printing a shorter unique SHA1.
There are other use cases as well (in scripts and other tools built on top of git) that I've used for:
--verify to verify that the specified object is a valid git object.--git-dir for displaying the abs/relative path of the the .git directory.--is-inside-git-dir or within a work-tree using --is-inside-work-tree --is-bare-repository --branches), tags (--tags) and the refs can also be filtered based on the remote (using --remote)--parse-opt to normalize arguments in a script (kind of similar to getopt) and print an output string that can be used with eval Massage just implies that it is possible to convert the info from one form into another i.e. a transformation command. These are some quick examples I can think of:
A..B for git log or git diff into the equivalent arguments for the underlying plumbing command as B ^A
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Just to elaborate on the etymology of the command name rev-parse, Git consistently uses the term rev in plumbing commands as short for "revision" and generally meaning the 40-character SHA1 hash for a commit. The command rev-list for example prints a list of 40-char commit hashes for a branch or whatever.
In this case the name might be expanded to parse-a-commitish-to-a-full-SHA1-hash. While the command has the several ancillary functions mentioned in Tuxdude's answer, its namesake appears to be the use case of transforming a user-friendly reference like a branch name or abbreviated hash into the unambiguous 40-character SHA1 hash most useful for many programming/plumbing purposes.
I know I was thinking it was "reverse-parse" something for quite a while before I figured it out and had the same trouble making sense of the terms "massaging" and "manipulation" :)
Anyway, I find this "parse-to-a-revision" notion a satisfying way to think of it, and a reliable concept for bringing this command to mind when I need that sort of thing. Frequently in scripting Git you take a user-friendly commit reference as user input and generally want to get it resolved to a validated and unambiguous working reference as soon after receiving it as possible. Otherwise input translation and validation tends to proliferate through the script.
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