git_tutorial.txt

GITTUTORIAL(7)                    Git Manual                    GITTUTORIAL(7)


NNAAMMEE
       gittutorial - A tutorial introduction to Git

SSYYNNOOPPSSIISS
       git *


DDEESSCCRRIIPPTTIIOONN
       This tutorial explains how to import a new project into Git, make
       changes to it, and share changes with other developers.

       If you are instead primarily interested in using Git to fetch a
       project, for example, to test the latest version, you may prefer to
       start with the first two chapters of TThhee GGiitt UUsseerr''ss MMaannuuaall[1].

       First, note that you can get documentation for a command such as ggiitt
       lloogg ----ggrraapphh with:

           $ man git-log


       or:

           $ git help log


       With the latter, you can use the manual viewer of your choice; see ggiitt--
       hheellpp(1) for more information.

       It is a good idea to introduce yourself to Git with your name and
       public email address before doing any operation. The easiest way to do
       so is:

           $ git config --global user.name "Your Name Comes Here"
           $ git config --global user.email you@yourdomain.example.com


IIMMPPOORRTTIINNGG AA NNEEWW PPRROOJJEECCTT
       Assume you have a tarball project.tar.gz with your initial work. You
       can place it under Git revision control as follows.

           $ tar xzf project.tar.gz
           $ cd project
           $ git init


       Git will reply

           Initialized empty Git repository in .git/


       You've now initialized the working directory--you may notice a new
       directory created, named ".git".

       Next, tell Git to take a snapshot of the contents of all files under
       the current directory (note the _.), with _g_i_t _a_d_d:

           $ git add .


       This snapshot is now stored in a temporary staging area which Git calls
       the "index". You can permanently store the contents of the index in the
       repository with _g_i_t _c_o_m_m_i_t:

           $ git commit


       This will prompt you for a commit message. You've now stored the first
       version of your project in Git.

MAKING CHANGES
       Modify some files, then add their updated contents to the index:

           $ git add file1 file2 file3


       You are now ready to commit. You can see what is about to be committed
       using _g_i_t _d_i_f_f with the --cached option:

           $ git diff --cached


       (Without --cached, _g_i_t _d_i_f_f will show you any changes that you've made
       but not yet added to the index.) You can also get a brief summary of
       the situation with _g_i_t _s_t_a_t_u_s:

           $ git status
           On branch master
           Changes to be committed:
           Your branch is up-to-date with 'origin/master'.
             (use "git reset HEAD <file>..." to unstage)

                   modified:   file1
                   modified:   file2
                   modified:   file3


       If you need to make any further adjustments, do so now, and then add
       any newly modified content to the index. Finally, commit your changes
       with:

           $ git commit


       This will again prompt you for a message describing the change, and
       then record a new version of the project.

       Alternatively, instead of running _g_i_t _a_d_d beforehand, you can use

           $ git commit -a


       which will automatically notice any modified (but not new) files, add
       them to the index, and commit, all in one step.

       A note on commit messages: Though not required, it's a good idea to
       begin the commit message with a single short (less than 50 character)
       line summarizing the change, followed by a blank line and then a more
       thorough description. The text up to the first blank line in a commit
       message is treated as the commit title, and that title is used
       throughout Git. For example, ggiitt--ffoorrmmaatt--ppaattcchh(1) turns a commit into
       email, and it uses the title on the Subject line and the rest of the
       commit in the body.

GGIITT TTRRAACCKKSS CCOONNTTEENNTT NNOOTT FFIILLEESS
       Many revision control systems provide an aadddd command that tells the
       system to start tracking changes to a new file. Git's aadddd command does
       something simpler and more powerful: _g_i_t _a_d_d is used both for new and
       newly modified files, and in both cases it takes a snapshot of the
       given files and stages that content in the index, ready for inclusion
       in the next commit.

VVIIEEWWIINNGG PPRROOJJEECCTT HHIISSTTOORRYY
       At any point you can view the history of your changes using

           $ git log


       If you also want to see complete diffs at each step, use

           $ git log -p


       Often the overview of the change is useful to get a feel of each step

           $ git log --stat --summary


MANAGING BRANCHES
       A single Git repository can maintain multiple branches of development.
       To create a new branch named "experimental", use

           $ git branch experimental


       If you now run

           $ git branch


       you'll get a list of all existing branches:

             experimental
           * master


       The "experimental" branch is the one you just created, and the "master"
       branch is a default branch that was created for you automatically. The
       asterisk marks the branch you are currently on; type

           $ git checkout experimental


       to switch to the experimental branch. Now edit a file, commit the
       change, and switch back to the master branch:

           (edit file)
           $ git commit -a
           $ git checkout master


       Check that the change you made is no longer visible, since it was made
       on the experimental branch and you're back on the master branch.

       You can make a different change on the master branch:

           (edit file)
           $ git commit -a


       at this point the two branches have diverged, with different changes
       made in each. To merge the changes made in experimental into master,
       run

           $ git merge experimental


       If the changes don't conflict, you're done. If there are conflicts,
       markers will be left in the problematic files showing the conflict;

           $ git diff


       will show this. Once you've edited the files to resolve the conflicts,

           $ git commit -a


       will commit the result of the merge. Finally,

           $ gitk


       will show a nice graphical representation of the resulting history.

       At this point you could delete the experimental branch with

           $ git branch -d experimental


       This command ensures that the changes in the experimental branch are
       already in the current branch.

       If you develop on a branch crazy-idea, then regret it, you can always
       delete the branch with

           $ git branch -D crazy-idea


       Branches are cheap and easy, so this is a good way to try something
       out.

UUSSIINNGG GGIITT FFOORR CCOOLLLLAABBOORRAATTIIOONN
       Suppose that Alice has started a new project with a Git repository in
       /home/alice/project, and that Bob, who has a home directory on the same
       machine, wants to contribute.

       Bob begins with:

           bob$ git clone /home/alice/project myrepo


       This creates a new directory "myrepo" containing a clone of Alice's
       repository. The clone is on an equal footing with the original project,
       possessing its own copy of the original project's history.

       Bob then makes some changes and commits them:

           (edit files)
           bob$ git commit -a
           (repeat as necessary)


       When he's ready, he tells Alice to pull changes from the repository at
       /home/bob/myrepo. She does this with:

           alice$ cd /home/alice/project
           alice$ git pull /home/bob/myrepo master


       This merges the changes from Bob's "master" branch into Alice's current
       branch. If Alice has made her own changes in the meantime, then she may
       need to manually fix any conflicts.

       The "pull" command thus performs two operations: it fetches changes
       from a remote branch, then merges them into the current branch.

       Note that in general, Alice would want her local changes committed
       before initiating this "pull". If Bob's work conflicts with what Alice
       did since their histories forked, Alice will use her working tree and
       the index to resolve conflicts, and existing local changes will
       interfere with the conflict resolution process (Git will still perform
       the fetch but will refuse to merge --- Alice will have to get rid of
       her local changes in some way and pull again when this happens).

       Alice can peek at what Bob did without merging first, using the "fetch"
       command; this allows Alice to inspect what Bob did, using a special
       symbol "FETCH_HEAD", in order to determine if he has anything worth
       pulling, like this:

           alice$ git fetch /home/bob/myrepo master
           alice$ git log -p HEAD..FETCH_HEAD


       This operation is safe even if Alice has uncommitted local changes. The
       range notation "HEAD..FETCH_HEAD" means "show everything that is
       reachable from the FETCH_HEAD but exclude anything that is reachable
       from HEAD". Alice already knows everything that leads to her current
       state (HEAD), and reviews what Bob has in his state (FETCH_HEAD) that
       she has not seen with this command.

       If Alice wants to visualize what Bob did since their histories forked
       she can issue the following command:

           $ gitk HEAD..FETCH_HEAD


       This uses the same two-dot range notation we saw earlier with _g_i_t _l_o_g.

       Alice may want to view what both of them did since they forked. She can
       use three-dot form instead of the two-dot form:

           $ gitk HEAD...FETCH_HEAD


       This means "show everything that is reachable from either one, but
       exclude anything that is reachable from both of them".

       Please note that these range notation can be used with both gitk and
       "git log".

       After inspecting what Bob did, if there is nothing urgent, Alice may
       decide to continue working without pulling from Bob. If Bob's history
       does have something Alice would immediately need, Alice may choose to
       stash her work-in-progress first, do a "pull", and then finally unstash
       her work-in-progress on top of the resulting history.

       When you are working in a small closely knit group, it is not unusual
       to interact with the same repository over and over again. By defining
       _r_e_m_o_t_e repository shorthand, you can make it easier:

           alice$ git remote add bob /home/bob/myrepo


       With this, Alice can perform the first part of the "pull" operation
       alone using the _g_i_t _f_e_t_c_h command without merging them with her own
       branch, using:

           alice$ git fetch bob


       Unlike the longhand form, when Alice fetches from Bob using a remote
       repository shorthand set up with _g_i_t _r_e_m_o_t_e, what was fetched is stored
       in a remote-tracking branch, in this case bboobb//mmaasstteerr. So after this:

           alice$ git log -p master..bob/master


       shows a list of all the changes that Bob made since he branched from
       Alice's master branch.

       After examining those changes, Alice could merge the changes into her
       master branch:

           alice$ git merge bob/master


       This mmeerrggee can also be done by _p_u_l_l_i_n_g _f_r_o_m _h_e_r _o_w_n _r_e_m_o_t_e_-_t_r_a_c_k_i_n_g
       _b_r_a_n_c_h, like this:

           alice$ git pull . remotes/bob/master


       Note that git pull always merges into the current branch, regardless of
       what else is given on the command line.

       Later, Bob can update his repo with Alice's latest changes using

           bob$ git pull


       Note that he doesn't need to give the path to Alice's repository; when
       Bob cloned Alice's repository, Git stored the location of her
       repository in the repository configuration, and that location is used
       for pulls:

           bob$ git config --get remote.origin.url
           /home/alice/project


       (The complete configuration created by _g_i_t _c_l_o_n_e is visible using ggiitt
       ccoonnffiigg --ll, and the ggiitt--ccoonnffiigg(1) man page explains the meaning of each
       option.)

       Git also keeps a pristine copy of Alice's master branch under the name
       "origin/master":

           bob$ git branch -r
             origin/master


       If Bob later decides to work from a different host, he can still
       perform clones and pulls using the ssh protocol:

           bob$ git clone alice.org:/home/alice/project myrepo


       Alternatively, Git has a native protocol, or can use http; see ggiitt--
       ppuullll(1) for details.

       Git can also be used in a CVS-like mode, with a central repository that
       various users push changes to; see ggiitt--ppuusshh(1) and ggiittccvvss--mmiiggrraattiioonn(7).

EEXXPPLLOORRIINNGG HHIISSTTOORRYY
       Git history is represented as a series of interrelated commits. We have
       already seen that the _g_i_t _l_o_g command can list those commits. Note that
       first line of each git log entry also gives a name for the commit:

           $ git log
           commit c82a22c39cbc32576f64f5c6b3f24b99ea8149c7
           Author: Junio C Hamano <junkio@cox.net>
           Date:   Tue May 16 17:18:22 2006 -0700

               merge-base: Clarify the comments on post processing.


       We can give this name to _g_i_t _s_h_o_w to see the details about this commit.

           $ git show c82a22c39cbc32576f64f5c6b3f24b99ea8149c7


       But there are other ways to refer to commits. You can use any initial
       part of the name that is long enough to uniquely identify the commit:

           $ git show c82a22c39c   # the first few characters of the name are
                                   # usually enough
           $ git show HEAD         # the tip of the current branch
           $ git show experimental # the tip of the "experimental" branch


       Every commit usually has one "parent" commit which points to the
       previous state of the project:

           $ git show HEAD^  # to see the parent of HEAD
           $ git show HEAD^^ # to see the grandparent of HEAD
           $ git show HEAD~4 # to see the great-great grandparent of HEAD


       Note that merge commits may have more than one parent:

           $ git show HEAD^1 # show the first parent of HEAD (same as HEAD^)
           $ git show HEAD^2 # show the second parent of HEAD


       You can also give commits names of your own; after running

           $ git tag v2.5 1b2e1d63ff


       you can refer to 1b2e1d63ff by the name "v2.5". If you intend to share
       this name with other people (for example, to identify a release
       version), you should create a "tag" object, and perhaps sign it; see
       ggiitt--ttaagg(1) for details.

       Any Git command that needs to know a commit can take any of these
       names. For example:

           $ git diff v2.5 HEAD     # compare the current HEAD to v2.5
           $ git branch stable v2.5 # start a new branch named "stable" based
                                    # at v2.5
           $ git reset --hard HEAD^ # reset your current branch and working
                                    # directory to its state at HEAD^


       Be careful with that last command: in addition to losing any changes in
       the working directory, it will also remove all later commits from this
       branch. If this branch is the only branch containing those commits,
       they will be lost. Also, don't use _g_i_t _r_e_s_e_t on a publicly-visible
       branch that other developers pull from, as it will force needless
       merges on other developers to clean up the history. If you need to undo
       changes that you have pushed, use _g_i_t _r_e_v_e_r_t instead.

       The _g_i_t _g_r_e_p command can search for strings in any version of your
       project, so

           $ git grep "hello" v2.5


       searches for all occurrences of "hello" in v2.5.

       If you leave out the commit name, _g_i_t _g_r_e_p will search any of the files
       it manages in your current directory. So

           $ git grep "hello"


       is a quick way to search just the files that are tracked by Git.

       Many Git commands also take sets of commits, which can be specified in
       a number of ways. Here are some examples with _g_i_t _l_o_g:

           $ git log v2.5..v2.6            # commits between v2.5 and v2.6
           $ git log v2.5..                # commits since v2.5
           $ git log --since="2 weeks ago" # commits from the last 2 weeks
           $ git log v2.5.. Makefile       # commits since v2.5 which modify
                                           # Makefile


       You can also give _g_i_t _l_o_g a "range" of commits where the first is not
       necessarily an ancestor of the second; for example, if the tips of the
       branches "stable" and "master" diverged from a common commit some time
       ago, then

           $ git log stable..master


       will list commits made in the master branch but not in the stable
       branch, while

           $ git log master..stable


       will show the list of commits made on the stable branch but not the
       master branch.

       The _g_i_t _l_o_g command has a weakness: it must present commits in a list.
       When the history has lines of development that diverged and then merged
       back together, the order in which _g_i_t _l_o_g presents those commits is
       meaningless.

       Most projects with multiple contributors (such as the Linux kernel, or
       Git itself) have frequent merges, and _g_i_t_k does a better job of
       visualizing their history. For example,

           $ gitk --since="2 weeks ago" drivers/


       allows you to browse any commits from the last 2 weeks of commits that
       modified files under the "drivers" directory. (Note: you can adjust
       gitk's fonts by holding down the control key while pressing "-" or
       "+".)

       Finally, most commands that take filenames will optionally allow you to
       precede any filename by a commit, to specify a particular version of
       the file:

           $ git diff v2.5:Makefile HEAD:Makefile.in


       You can also use _g_i_t _s_h_o_w to see any such file:

           $ git show v2.5:Makefile


NNEEXXTT SSTTEEPPSS
       This tutorial should be enough to perform basic distributed revision
       control for your projects. However, to fully understand the depth and
       power of Git you need to understand two simple ideas on which it is
       based:

       +o   The object database is the rather elegant system used to store the
           history of your project--files, directories, and commits.

       +o   The index file is a cache of the state of a directory tree, used to
           create commits, check out working directories, and hold the various
           trees involved in a merge.

       Part two of this tutorial explains the object database, the index file,
       and a few other odds and ends that you'll need to make the most of Git.
       You can find it at ggiittttuuttoorriiaall--22(7).

       If you don't want to continue with that right away, a few other
       digressions that may be interesting at this point are:

       +o   ggiitt--ffoorrmmaatt--ppaattcchh(1), ggiitt--aamm(1): These convert series of git commits
           into emailed patches, and vice versa, useful for projects such as
           the Linux kernel which rely heavily on emailed patches.

       +o   ggiitt--bbiisseecctt(1): When there is a regression in your project, one way
           to track down the bug is by searching through the history to find
           the exact commit that's to blame. Git bisect can help you perform a
           binary search for that commit. It is smart enough to perform a
           close-to-optimal search even in the case of complex non-linear
           history with lots of merged branches.

       +o   ggiittwwoorrkkfflloowwss(7): Gives an overview of recommended workflows.

       +o   ggiitteevveerryyddaayy(7): Everyday Git with 20 Commands Or So.

       +o   ggiittccvvss--mmiiggrraattiioonn(7): Git for CVS users.

SSEEEE AALLSSOO
       ggiittttuuttoorriiaall--22(7), ggiittccvvss--mmiiggrraattiioonn(7), ggiittccoorree--ttuuttoorriiaall(7),
       ggiittgglloossssaarryy(7), ggiitt--hheellpp(1), ggiittwwoorrkkfflloowwss(7), ggiitteevveerryyddaayy(7), TThhee GGiitt
       UUsseerr''ss MMaannuuaall[1]

GGIITT
       Part of the ggiitt(1) suite.

NNOOTTEESS
        1. The Git User's Manual
           git-htmldocs/user-manual.html


Git 2.10.0                        09/02/2016                    GITTUTORIAL(7)