Greg Vaughn posted this cool alias the other day:
copr = "!f() { git fetch -fu origin refs/pull/$1/head:pr-$1; git checkout pr-$1; } ; f"
Preferring to be a stock-tools person, I wanted to deconstruct this to see how I'd use it off-the-shelf without the alias.
git fetch -- I'm already familiar with this command
-fu -- these two flags I'm not sure are necessary, esp. -u since the help says,
"unless you are implementing your own Porcelain you are not supposed to use
it." - and since I don't know what Porcelain is, I presume I'm in the general camp.
origin -- I also know this is the repo (the remote name from `git remote`)
Now to some new stuff for my brain:
refs/pull/$1/head:pr-$1
I know the $1 is just a variable for the PR number. This whole thing is the refspec according to git help fetch:
<refspec>
The format of a <refspec> parameter is an optional plus +, followed by the source ref <src>,
followed by a colon :, followed by the destination ref <dst>.
The remote ref that matches <src> is fetched, and if <dst> is not empty string, the local ref
that matches it is fast-forwarded using <src>. If the optional plus + is used, the local ref is
updated even if it does not result in a fast-forward update.
Since I have a git completion script installed, I realize I can see the list of available refspecs with:
git fetch origin [<tab><tab>]
[chrismo@momac foo (master)]$ git fetch origin
HEAD:HEAD refs/pull/2/merge:refs/pull/2/merge
master:master refs/pull/3/head:refs/pull/3/head
refs/pull/2/head:refs/pull/2/head refs/pull/3/merge:refs/pull/3/merge
These can be explicitly listed (without auto-completion magic) with git ls-remote origin
[chrismo@momac foo (master)]$ git ls-remote origin
f2720fe21c9e6b92ede4f9f99598f60d3251b0b1 HEAD
f2720fe21c9e6b92ede4f9f99598f60d3251b0b1 refs/heads/master
594fe52884ca771c26a70a45402f9cfedf58c3ae refs/pull/2/head
3dd41b7ac6db8160e61ee89d920894ab20ea0b28 refs/pull/2/merge
00d5916224d47fa99cf76ceb5e2b81ca76cd1f62 refs/pull/3/head
07f43e1ce5ae8abc3afb2d27b5a845de67819029 refs/pull/3/merge
Back to the refspec help from the fetch command, I see that refs/pull/2/head is the src and whatever is on the right side of the colon is the dst. So ...
git fetch origin refs/pull/2/head:pr-2
... simply means, fetch the contents of pull request 2 and put it into a new local branch called pr-2 -- the destination local branch could be named whatever I want.