How is a tag different from a branch in Git Which should I use here

Question

I am having some difficulty understanding how to use tags versus branches in git   I just moved the current version of our code from cvs to git  and now I m going to be working on a subset of that code for a particular feature  A few other developers will be working on this as well  but not all developers in our group are going to care about this feature  Should I be creating a branch or a tag  In what situations should I be using one versus the other

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simple      Tags are expected to always point at the same version of a project  while heads are expected to advance as development progresses    Git User Manual

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The Git Parable explains how a typical DVCS gets created and why their creators did what they did  Also  you might want to take a look at Git for Computer Scientist  it explains what each type of object in Git does  including branches and tags

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Tags can be either signed or unsigned  branches are never signed   Signed tags can never move because they are cryptographically bound  with a signature  to a particular commit  Unsigned tags are not bound and it is possible to move them  but moving tags is not a normal use case    Branches can not only move to a different commit but are expected to do so  You should use a branch for your local development project  It doesn t quite make sense to commit work to a Git repository  on a tag

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A tag is used to mark a version  more specifically it references a point in time on a branch  A branch is typically used to add features to a project

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Branches are made of wood and grow from the trunk of the tree   Tags are made of paper  derivative of wood  and hang like Christmas Ornaments from various places in the tree   Your project is the tree  and your feature that will be added to the project will grow on a branch   The answer is branch

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A tag represents a version of a particular branch at a moment in time   A branch represents a separate thread of development that may run concurrently with other development efforts on the same code base   Changes to a branch may eventually be merged back into another branch to unify them   Usually you ll tag a particular version so that you can recreate it  e g   this is the version we shipped to XYZ Corp    A branch is more of a strategy to provide on-going updates on a particular version of the code while continuing to do development on it   You ll make a branch of the delivered version  continue development on the main line  but make bug fixes to the branch that represents the delivered version   Eventually  you ll merge these bug fixes back into the main line   Often you ll use both branching and tagging together   You ll have various tags that may apply both to the main line and its branches marking particular versions  those delivered to customers  for instance  along each branch that you may want to recreate -- for delivery  bug diagnosis  etc   It s actually more complicated than this -- or as complicated as you want to make it -- but these examples should give you an idea of the differences

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If you think of your repository as a book that chronicles progress on your project     Branches  You can think of a branch as one of those sticky bookmarks     A brand new repository has only one of those  called master   which automatically moves to the latest page  think commit  you ve written  However  you re free to create and use more bookmarks  in order to mark other points of interest in the book  so you can return to them quickly    Also  you can always move a particular bookmark to some other page of the book  using git-reset  for instance   points of interest typically vary over time   Tags  You can think of tags as chapter headings     It may contain a title  think annotated tags  or not  A tag is similar but different to a branch  in that it marks a point of historical interest in the book   To maintain its historical aspect  once you ve shared a tag  i e  pushed it to a shared remote   you re not supposed to move it to some other place in the book

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From the theoretical point of view    tags are symbolic names for a given revision   They always point to the same object  usually  to the same revision   they do not change  branches are symbolic names for line of development   New commits are created on top of branch   The branch pointer naturally advances  pointing to newer and newer commits      From the technical point of view    tags reside in refs tags  namespace  and can point to tag objects  annotated and optionally GPG signed tags  or directly to commit object  less used lightweight tag for local names   or in very rare cases even to tree object or blob object  e g  GPG signature   branches reside in refs heads  namespace  and can point only to commit objects   The HEAD pointer must refer to a branch  symbolic reference  or directly to a commit  detached HEAD or unnamed branch   remote-tracking branches reside in refs remotes  lt remote gt   namespace  and follow ordinary branches in remote repository  lt remote gt       See also gitglossary manpage      branch             A  branch  is an active line of development  The most recent commit on a branch is referred to as the tip of that branch  The tip of the branch is referenced by a branch head  which moves forward as additional development is done on the branch  A single git repository can track an arbitrary number of branches  but your working tree is associated with just one of them  the  current  or  checked out  branch   and HEAD points to that branch          tag           A ref pointing to a tag or commit object  In contrast to a head  a tag is not changed by a commit  Tags  not tag objects  are stored in  GIT DIR refs tags          A tag is most typically used to mark a particular point in the commit ancestry chain          tag object           An object containing a ref pointing to another object  which can contain a message just like a commit object  It can also contain a  PGP  signature  in which case it is called a  signed tag object

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What you need to realize  coming from CVS  is that you no longer create directories when setting up a branch  No more  sticky tag   which can be applied to just one file   or  branch tag   Branch and tags are two different objects in Git  and they always apply to the all repo   You would no longer  with SVN this time  have to explicitly structure your repository with   branches    myFirstBranch      myProject        mySubDirs    mySecondBranch          tags    myFirstTag      myProject        mySubDirs    mySecondTag          That structure comes from the fact CVS is a revision system and not a version system  see Source control vs  Revision Control    That means branches are emulated through tags for CVS  directory copies for SVN   Your question makes senses if you are used to checkout a tag  and start working in it  Which you shouldn t    A tag is supposed to represent an immutable content  used only to access it with the guarantee to get the same content every time   In Git  the history of revisions is a series of commits  forming a graph  A branch is one path of that graph  x--x--x--x--x   one branch             --y----y   another branch        1 1                               a tag pointing to a commit    If you checkout a tag  you will need to create a branch to start working from it  If you checkout a branch  you will directly see the latest commit it  HEAD   of that branch    See Jakub Narebski s answer for all the technicalities  but frankly  at this point  you do not need  yet  all the details     The main point is  a tag being a simple pointer to a commit  you will never be able to modify its content  You need a branch     In your case  each developer working on a specific feature    should create their own branch in their respective repository track branches from their colleague s repositories  the one working on the same feature  pulling pushing in order to share your work with your peers    Instead of tracking directly the branches of your colleagues  you could track only the branch of one  official  central repository to which everyone pushes his her work in order to integrate and share everyone s work for this particular feature

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the simple answer is      branch    the current branch pointer moves with every commit to the repository   but     tag  the commit that a tag points doesn t change  in fact the tag is a snapshot of that commit

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I like to think of branches as where you re going  tags as where you ve been   A tag feels like a bookmark of a particular important point in the past  such as a version release   Whereas a branch is a particular path the project is going down  and thus the branch marker advances with you  When you re done you merge delete the branch  i e  the marker   Of course  at that point you could choose to tag that commit

User · Answer

It looks like the best way to explain is that tags act as read only branches   You can use a branch as a tag  but you may inadvertently update it with new commits   Tags are guaranteed to point to the same commit as long as they exist

[git] How is a tag different from a branch in Git? Which should I use, here?

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