How can I preview a merge in git

Question

I have a git branch  the mainline  for example  and I want to merge in another development branch  Or do I   In order to decide whether I really want to merge this branch in  i d like to see some sort of preview of what the merge will do  Preferably with the ability to see the list of commits that are being applied   So far  the best I can come up with is merge --no-ff --no-commit  and then diff HEAD

User · Accepted Answer

I ve found that the solution the works best for me is to just perform the merge and abort it if there are conflicts  This particular syntax feels clean and simple to me  This is Strategy 2 below  However  if you want to ensure you don t mess up your current branch  or you re just not ready to merge regardless of the existence of conflicts  simply create a new sub-branch off of it and merge that  Strategy 1  The safe way     merge off a temporary branch  git checkout mybranch git checkout -b mynew-temporary-branch git merge some-other-branch  That way you can simply throw away the temporary branch if you just want to see what the conflicts are  You don t need to bother  quot aborting quot  the merge  and you can go back to your work -- simply checkout  mybranch  again and you won t have any merged code or merge conflicts in your branch  This is basically a dry-run  Strategy 2  When you definitely want to merge  but only if there aren t conflicts git checkout mybranch git merge some-other-branch  If git reports conflicts  and ONLY IF THERE ARE conflicts  you can then do  git merge --abort  If the merge is successful  you cannot abort it  only reset   If you re not ready to merge  use the safer way above   EDIT  2016-Nov - I swapped strategy 1 for 2  because it seems to be that most people are looking for  quot the safe way quot   Strategy 2 is now more of a note that you can simply abort the merge if the merge has conflicts that you re not ready to deal with  Keep in mind if reading comments

User · Answer

If you re like me  you re looking for equivalent to svn update -n  The following appears to do the trick  Note that make sure to do a git fetch first so that your local repo has the appropriate updates to compare against     git fetch origin   git diff --name-status origin master D       TableAudit Step0 DeleteOldFiles sh D       TableAudit Step1 PopulateRawTableList sh A       manbuild staff companies sql M       update-all-slave-dbs sh   or if you want a diff from your head to the remote     git fetch origin   git diff origin master     IMO this solution is much easier and less error prone  and therefore much less risky  than the top solution which proposes  merge then abort

User · Answer

If you already fetched the changes  my favourite is   git log      u    That needs git 1 7 x I believe though  The    u  notation is a  shorthand  for the upstream branch so it s a little more versatile than git log    origin master   Note  If you use zsh and the extended glog thing on  you likely have to do something like   git log       u

User · Answer

git log currentbranch  otherbranch will give you the list of commits that will go into the current branch if you do a merge  The usual arguments to log which give details on the commits will give you more information    git diff currentbranch otherbranch will give you the diff between the two commits that will become one  This will be a diff that gives you everything that will get merged    Would these help

User · Answer

I do not want to use the git merge command as the precursor to reviewing conflicting files   I don t want to do a merge  I want to identify potential problems before I merge - problems that auto-merge might hide from me   The solution I have been searching for is how to have git spit out a list of files that have been changed in both branches that will be merged together in the future  relative to some common ancestor   Once I have that list  I can use other file comparison tools to scout things out further   I have searched multiple times  and I still haven t found what I want in a native git command     Here is my workaround  in case it helps anyone else out there   In this scenario I have a branch called QA that has many changes in it since the last production release   Our last production release is tagged with  15 20 1    I have another development branch called new stuff that I want to merge into the QA branch   Both QA and new stuff point to commits that  follow   as reported by gitk  the 15 20 1 tag    git checkout QA git pull git diff 15 20 1 --name-only  gt  QA files git checkout new stuff git pull git diff 15 20 1 --name-only  gt  new stuff files comm -12 QA files new stuff files   Here are some discussions that hit on why I m interested in targeting these specific files   How can I trust Git merge   https   softwareengineering stackexchange com questions 199780 how-far-do-you-trust-automerge

User · Answer

Adding to the existing answers  an alias could be created to show the diff and or log prior to a merge   Many answers omit the fetch to be done first before  previewing  the merge  this is an alias that combines these two steps into one  emulating something similar to mercurial s hg incoming   outgoing   So  building on  git log   otherbranch   you can add the following to    gitconfig         alias        fetch and show what would be merged  use option  -p  to see patch      incoming     git remote update -p  git log     u     For symmetry  the following alias can be used to show what is committed and would be pushed  prior to pushing         what would be pushed  currently committed      outgoing   log   u      And then you can run  git incoming  to show a lot of changes  or  git incoming -p  to show the patch  i e   the  diff     git incoming --pretty oneline   for a terse summary  etc  You may then  optionally  run  git pull  to actually merge    Though  since you ve already fetched  the merge could be done directly    Likewise   git outgoing  shows what would be pushed if you were to run  git push

User · Answer

Maybe this can help you    git-diff-tree - Compares the content and mode of blobs found via two tree objects

User · Answer

Pull Request - I ve used most of the already submitted ideas but one that I also often use is   especially if its from another dev   doing a Pull Request which gives a handy way to review all of the changes in a merge before it takes place   I know that is GitHub not git but it sure is handy

User · Answer

Short of actually performing the merge in a throw away fashion  see Kasapo s answer   there doesn t seem to be a reliable way of seeing this   Having said that  here s a method that comes marginally close   git log TARGET BRANCH   SOURCE BRANCH --cherry   This gives a fair indication of which commits will make it into the merge   To see diffs  add -p   To see file names  add any of --raw  --stat  --name-only  --name-status   The problem with the git diff TARGET BRANCH   SOURCE BRANCH approach  see Jan Hudec s answer  is  you ll see diffs for changes already in your target branch if your source branch contains cross merges

User · Answer

git log   otherbranchlist of changes that will be merged into current branch  git diff    otherbranchdiff from common ancestor  merge base  to the head of what will be merged  Note the three dots  which have a special meaning compared to two dots  see below   gitk    otherbranchgraphical representation of the branches since they were merged last time    Empty string implies HEAD  so that s why just   otherbranch instead of HEAD  otherbranch   The two vs  three dots have slightly different meaning for diff than for the commands that list revisions  log  gitk etc    For log and others two dots  a  b  means everything that is in b but not a and three dots  a   b  means everything that is in only one of a or b  But diff works with two revisions and there the simpler case represented by two dots  a  b  is simple difference from a to b and three dots  a   b  mean difference between common ancestor and b  git diff   git merge-base a b   b

User · Answer

Most answers here either require a clean working directory and multiple interactive steps  bad for scripting   or don t work for all cases  e g  past merges which already bring some of the outstanding changes into your target branch  or cherry-picks doing the same   To truly see what would change in the master branch if you merged develop into it  right now   git merge-tree   git merge-base master develop  master develop      As it s a plumbing command  it does not guess what you mean  you have to be explicit  It also doesn t colorize the output or use your pager  so the full command would be    git merge-tree   git merge-base master develop  master develop   colordiff   less -R       https   git seveas net previewing-a-merge-result html   thanks to David Normington for the link   P S    If you would get merge conflicts  they will show up with the usual conflict markers in the output  e g      git merge-tree   git merge-base a b   a b  added in both   our    100644 78981922613b2afb6025042ff6bd878ac1994e85 a   their  100644 61780798228d17af2d34fce4cfbdf35556832472 a    -1  1 5      lt  lt  lt  lt  lt  lt  lt   our  a           b   gt  gt  gt  gt  gt  gt  gt   their   User  dreftymac makes a good point  this makes it unsuitable for scripting  because you can t easily catch that from the status code  The conflict markers can be quite different depending on circumstance  deleted vs modified  etc   which makes it hard to grep  too  Beware

[git] How can I preview a merge in git?

Strategy 1: The safe way – merge off a temporary branch:

Strategy 2: When you definitely want to merge, but only if there aren't conflicts

Examples related to git

Examples related to git-merge