# specifying "fast-forward" only in git-pull 3 messages from 2007-03-28 to 2007-03-28. Participants: David Tweed, Junio C Hamano, Shawn O. Pearce. Thread: https://gitlist.dev/t/7457 ## David Tweed, 2007-03-28 21:12 Subject: specifying "fast-forward" only in git-pull Message-ID: URL: https://gitlist.dev/e/e1dab3980703281412m78c2481bj9b9f7ec885dbbe4f%40mail.gmail.com ``` Hi, I'm looking through the documentation on git-pull and I see that I can specify a particular (sequence of) merge strategies, but I can't see a way to say "only do a fast forward, stopping if a fast forward doesn't apply". (Fast-forward doesn't appear to be a named strategy, which is why I can't use it with -s). Is there a way to do this? Rationale: I have a repository on several machines that are synchronised via usb-stick. 99.9% of the time a fast forward is all that is needed, and for scripting the synchronisation I'd like to restrict it so that only fast-forwards can happen automatically and everything else I have to do by invoking git myself. (Somehow I managed to get a merge that gave a weird result without me actually noticing for a couple of days, which combined with my chronological version scripts seemed to put new trees onto an unnamed branch. I've got the repo sorted out now, but I want to avoid the same issue in future.) Many thanks for any help. -- cheers, dave tweed__________________________ david.tweed@gmail.com Rm 124, School of Systems Engineering, University of Reading. Details are all that matters; God dwells there, and you never get to see Him if you don't struggle to get them right. -- Stephen Jay Gould ``` ## Junio C Hamano, 2007-03-28 21:26 Subject: Re: specifying "fast-forward" only in git-pull Message-ID: <7vbqidf4a8.fsf@assigned-by-dhcp.cox.net> URL: https://gitlist.dev/e/7vbqidf4a8.fsf%40assigned-by-dhcp.cox.net In-Reply-To: ``` "David Tweed" writes: > Hi, I'm looking through the documentation on git-pull and > I see that I can specify a particular (sequence of) merge > strategies, but I can't see a way to say "only do a fast > forward, stopping if a fast forward doesn't apply". > (Fast-forward doesn't appear to be a named strategy, > which is why I can't use it with -s). Is there a way to > do this? > > Rationale: I have a repository on several machines that > are synchronised via usb-stick. 99.9% of the time a fast > forward is all that is needed, and for scripting the > synchronisation I'd like to restrict it so that only > fast-forwards can happen automatically and everything > else I have to do by invoking git myself. Presumably you are scripting around "git pull" and wondering if there is a way to let you say "git pull -s ffonly $stick". Why don't you script around "git fetch" instead? #!/bin/sh stick=$1 git fetch "$stick" not_in_stick=$(git rev-list FETCH_HEAD..HEAD) if test -z "$not_in_stick" then : stick fast forwards git merge FETCH_HEAD else echo >&2 "Our HEAD has things the stick does not." exit 1 fi ``` ## Shawn O. Pearce, 2007-03-28 21:30 Subject: Re: specifying "fast-forward" only in git-pull Message-ID: <20070328213006.GO13247@spearce.org> URL: https://gitlist.dev/e/20070328213006.GO13247%40spearce.org In-Reply-To: ``` David Tweed wrote: > Hi, I'm looking through the documentation on git-pull and > I see that I can specify a particular (sequence of) merge > strategies, but I can't see a way to say "only do a fast > forward, stopping if a fast forward doesn't apply". > (Fast-forward doesn't appear to be a named strategy, > which is why I can't use it with -s). Is there a way to > do this? > > Rationale: I have a repository on several machines that > are synchronised via usb-stick. 99.9% of the time a fast > forward is all that is needed, and for scripting the > synchronisation I'd like to restrict it so that only > fast-forwards can happen automatically and everything > else I have to do by invoking git myself. (Somehow I managed to get > a merge that gave a weird result without me actually > noticing for a couple of days, which combined with > my chronological version scripts seemed to put new > trees onto an unnamed branch. I've got the repo sorted > out now, but I want to avoid the same issue in future.) If you are running a pull automatically and want to make sure its strictly a fast-forward, use something like: git fetch && b=$(git merge-base FETCH_HEAD HEAD) && test $b = $(git rev-parse HEAD^0) && git merge FETCH_HEAD The idea here is that if the merge base of the current branch and the incoming branch is the current branch, then the incoming branch is a superset of the current branch, and git-merge will perform a fast-forward. -- Shawn. ```