# using rev-list to tell if a branch is behind or ahead

2 messages from 2008-05-20 to 2008-05-20. Participants: Tim Harper, Shawn O. Pearce.
Thread: https://gitlist.dev/t/13590

## Tim Harper, 2008-05-20 20:14

Subject: using rev-list to tell if a branch is behind or ahead
Message-ID: <3703BF54-3619-432F-8B65-09AF17299CAD@gmail.com>
URL: https://gitlist.dev/e/3703BF54-3619-432F-8B65-09AF17299CAD%40gmail.com

```
I'm implementing a ruby interface to git and am wanting to be able to  
ask if a branch is ahead or behind.

I looked in the builtin-checkout.c file and see this code:

	/* Run "rev-list --left-right ours...theirs" internally... */
	rev_argc = 0;
	rev_argv[rev_argc++] = NULL;
	rev_argv[rev_argc++] = "--left-right";
	rev_argv[rev_argc++] = symmetric;
	rev_argv[rev_argc++] = "--";
	rev_argv[rev_argc] = NULL;

	strcpy(symmetric, sha1_to_hex(ours->object.sha1));
	strcpy(symmetric + 40, "...");
	strcpy(symmetric + 43, sha1_to_hex(theirs->object.sha1));

	init_revisions(&revs, NULL);
	setup_revisions(rev_argc, rev_argv, &revs, NULL);
	prepare_revision_walk(&revs);

	/* ... and count the commits on each side. */
	num_ours = 0;
	num_theirs = 0;
	while (1) {
		struct commit *c = get_revision(&revs);
		if (!c)
			break;
		if (c->object.flags & SYMMETRIC_LEFT)
			num_ours++;
		else
			num_theirs++;
	}


It looks like it's calling rev-parse.  But, when I call it with the  
same arguments (using branches or commit sha1's), it only will list  
commits that are in right and not in left.  I need it to show both  
ways: commits that are in the right and not in left, and commits that  
are in the left but not in right.

Do I need to call rev-parse twice to achieve this?

Here's a sample of what I'm trying currently:
~ $ mkdir test
~ $ cd test/
~/test $ git init
Initialized empty Git repository in .git/
~/test $ git
~/test $ echo content > file.txt
~/test $ git add file.txt && git commit -m "Initial commit"
Created initial commit f5e4160: Initial commit
  1 files changed, 1 insertions(+), 0 deletions(-)
  create mode 100644 file.txt
~/test master$ git co -b task
Switched to a new branch "task"
~/test task$ echo changes >> file.txt
~/test task$ git add file.txt && git commit -m "Some changes"
Created commit 96492ee: Some changes
  1 files changed, 1 insertions(+), 0 deletions(-)
~/test task$ git rev-list --left-right task..master --
~/test task$ git rev-list --left-right master..task --
 >96492ee80143f43417b00699ff29330d0027df7f


Thanks,

Tim

```

## Shawn O. Pearce, 2008-05-20 20:24

Subject: Re: using rev-list to tell if a branch is behind or ahead
Message-ID: <20080520202438.GG29038@spearce.org>
URL: https://gitlist.dev/e/20080520202438.GG29038%40spearce.org
In-Reply-To: <3703BF54-3619-432F-8B65-09AF17299CAD@gmail.com>

```
Tim Harper <timcharper@gmail.com> wrote:
> I'm implementing a ruby interface to git and am wanting to be able to  
> ask if a branch is ahead or behind.
> 
> I looked in the builtin-checkout.c file and see this code:
> 
> 	/* Run "rev-list --left-right ours...theirs" internally... */
...
> It looks like it's calling rev-parse.  But, when I call it with the  
> same arguments (using branches or commit sha1's), it only will list  
> commits that are in right and not in left.  I need it to show both  
> ways: commits that are in the right and not in left, and commits that  
> are in the left but not in right.
> 
> Do I need to call rev-parse twice to achieve this?

No.  You need to use the triple dot operator ("...") not the
double dot operator ("..").

> Here's a sample of what I'm trying currently:
> ~ $ mkdir test
> ~ $ cd test/
> ~/test $ git init
> Initialized empty Git repository in .git/
> ~/test $ git
> ~/test $ echo content > file.txt
> ~/test $ git add file.txt && git commit -m "Initial commit"
> Created initial commit f5e4160: Initial commit
>  1 files changed, 1 insertions(+), 0 deletions(-)
>  create mode 100644 file.txt
> ~/test master$ git co -b task
> Switched to a new branch "task"
> ~/test task$ echo changes >> file.txt
> ~/test task$ git add file.txt && git commit -m "Some changes"
> Created commit 96492ee: Some changes
>  1 files changed, 1 insertions(+), 0 deletions(-)
> ~/test task$ git rev-list --left-right task..master --

You need an extra "." between task and master, this should be:

  git rev-list --left-right task...master --

> ~/test task$ git rev-list --left-right master..task --
> >96492ee80143f43417b00699ff29330d0027df7f

-- 
Shawn.

```