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This tutorial will cover fast-forwarding when merging branches in Git.

Git is a version control system used in collaborative development environments to track changes made to files.

In a Git repository, we create many branches from the mainline branch for different purposes. We may eventually merge changes from these branches into the mainline branch to provide a release.

Sometimes the target branch is simply fast-forwarded by Git during a merge, rather than doing an actual merge.

We will now illustrate this with an example.

Fast-forward merges in Git

In a collaborative development environment, we may create multiple branches from the mainline branch in a Git repository. For example, for a bug fix, we create a branch, and say we may create another branch for feature development purposes.

Eventually, we merge these branches into the mainline branch to integrate the changes from these branches to provide a cohesive build.

Sometimes, we create a branch from the mainline branch, work on it, and make some commits on the new branch. Then, we decide to merge this branch with our mainline branch.

Now, if there is a linear path from the current branch tip to the target branch (mainline branch), then a fast-forward of the branch occurs instead of a merge commit in the target (mainline) branch.

Suppose we have a feature1branch called ; we are merging feature1changes from into our mainline branch main.

Now, suppose that commit mainof branch -i HEADis feature1an ancestor of commit of branch -i, the one we want to merge.

In this case, there is no need to merge branches, and all Git needs to do to integrate history is to move (i.e.) fast-forward the current branch tip to the target branch tip.

So, in our example, by fast-forwarding, mainthe current position of the branch HEADwill move up to feature1the branch tip.

mainPlease see the following figure for the situation of branches and before merging feature1.

              E---F---G feature1
             /
A---B---C---D main

So, in this case, when we git mergemerge two branches using the command, a fast-forward will occur.

To do the merge, we execute the following command.

$ git merge feature1

After executing the command, mainthe branch will be fast-forwarded.

See the fast forward illustration below.

              E---F---G feature1, main
             /
A---B---C---D

So now mainthe branch's current HEADis fast-forwarded. Git does not create a merge commit in this case.

Therefore, we have covered in detail the fast-forward operation when merging branches in Git.