From: J. Bruce Fields Date: Sun, 21 May 2006 20:54:05 +0000 (-0400) Subject: tutorial: expanded discussion of commit history X-Git-Tag: v1.4.0-rc1~103 X-Git-Url: https://git.tokkee.org/?a=commitdiff_plain;h=f1fe3846e4236a05879d7f84b11ae8ea64dd8d0d;p=git.git tutorial: expanded discussion of commit history Expand the history-browsing section of the tutorial a bit, in part to address Junio's suggestion that we mention "git grep" and Linus's complaint that people are missing the flexibility of the commandline interfaces for selecting commits. This reads a little more like a collection of examples than a "tutorial", but maybe that's what people need at this point. Signed-off-by: J. Bruce Fields Signed-off-by: Junio C Hamano --- diff --git a/Documentation/tutorial.txt b/Documentation/tutorial.txt index cd0f0df59..4c298c6e7 100644 --- a/Documentation/tutorial.txt +++ b/Documentation/tutorial.txt @@ -288,103 +288,162 @@ Git can also be used in a CVS-like mode, with a central repository that various users push changes to; see gitlink:git-push[1] and link:cvs-migration.html[git for CVS users]. -Keeping track of history ------------------------- +Exploring history +----------------- -Git history is represented as a series of interrelated commits. The -most recent commit in the currently checked-out branch can always be -referred to as HEAD, and the "parent" of any commit can always be -referred to by appending a caret, "^", to the end of the name of the -commit. So, for example, +Git history is represented as a series of interrelated commits. We +have already seen that the git log command can list those commits. +Note that first line of each git log entry also gives a name for the +commit: ------------------------------------- -git diff HEAD^ HEAD +$ git log +commit c82a22c39cbc32576f64f5c6b3f24b99ea8149c7 +Author: Junio C Hamano +Date: Tue May 16 17:18:22 2006 -0700 + + merge-base: Clarify the comments on post processing. ------------------------------------- -shows the difference between the most-recently checked-in state of -the tree and the previous state, and +We can give this name to git show to see the details about this +commit. ------------------------------------- -git diff HEAD^^ HEAD^ +$ git show c82a22c39cbc32576f64f5c6b3f24b99ea8149c7 ------------------------------------- -shows the difference between that previous state and the state two -commits ago. Also, HEAD~5 can be used as a shorthand for HEAD{caret}{caret}{caret}{caret}{caret}, -and more generally HEAD~n can refer to the nth previous commit. -Commits representing merges have more than one parent, and you can -specify which parent to follow in that case; see -gitlink:git-rev-parse[1]. +But there other ways to refer to commits. You can use any initial +part of the name that is long enough to uniquely identify the commit: -The name of a branch can also be used to refer to the most recent -commit on that branch; so you can also say things like +------------------------------------- +$ 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 has at least one "parent" commit, which points to the +previous state of the project: ------------------------------------- -git diff HEAD experimental +$ 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 ------------------------------------- -to see the difference between the most-recently committed tree in -the current branch and the most-recently committed tree in the -experimental branch. +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 +------------------------------------- -But you may find it more useful to see the list of commits made in -the experimental branch but not in the current branch, and +You can also give commits names of your own; after running ------------------------------------- -git log HEAD..experimental +$ git-tag v2.5 1b2e1d63ff ------------------------------------- -will do that, just as +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 +gitlink:git-tag[1] for details. + +Any git command that needs to know a commit can take any of these +names. For example: ------------------------------------- -git log experimental..HEAD +$ 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 its state at HEAD^ ------------------------------------- -will show the list of commits made on the HEAD but not included in -experimental. +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 "git reset" on a +publicly-visible branch that other developers pull from, as git will +be confused by history that disappears in this way.) -You can also give commits convenient names of your own: after running +The git grep command can search for strings in any version of your +project, so ------------------------------------- -$ git-tag v2.5 HEAD^^ +$ git grep "hello" v2.5 ------------------------------------- -you can refer to HEAD^^ 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 -gitlink:git-tag[1] for details. +searches for all occurences of "hello" in v2.5. -You can revisit the old state of a tree, and make further -modifications if you wish, using git branch: the command +If you leave out the commit name, git grep will search any of the +files it manages in your current directory. So ------------------------------------- -$ git branch stable-release v2.5 +$ git grep "hello" ------------------------------------- -will create a new branch named "stable-release" starting from the -commit which you tagged with the name v2.5. +is a quick way to search just the files that are tracked by git. -You can reset the state of any branch to an earlier commit at any -time with +Many git commands also take sets of commits, which can be specified +in a number of ways. Here are some examples with git log: ------------------------------------- -$ git reset --hard v2.5 +$ 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 ------------------------------------- -This will remove all later commits from this branch and reset the -working tree to the state it had when the given commit was made. If -this branch is the only branch containing the later commits, those -later changes will be lost. Don't use "git reset" on a -publicly-visible branch that other developers pull from, as git will -be confused by history that disappears in this way. +You can also give git log a "range" of commits where the first is not +necessarily an ancestor of the second; for example, if the tips of +the branches "stable-release" and "master" diverged from a common +commit some time ago, then + +------------------------------------- +$ git log stable..experimental +------------------------------------- + +will list commits made in the experimental branch but not in the +stable branch, while + +------------------------------------- +$ git log experimental..stable +------------------------------------- + +will show the list of commits made on the stable branch but not +the experimental branch. + +The "git log" 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 "git log" presents +those commits is meaningless. + +Most projects with multiple contributors (such as the linux kernel, +or git itself) have frequent merges, and gitk 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. + +Finally, most commands that take filenames will optionally allow you +to precede any filename by a commit, to specify a particular version +fo the file: + +------------------------------------- +$ git diff v2.5:Makefile HEAD:Makefile.in +------------------------------------- Next Steps ---------- Some good commands to explore next: - * gitlink:git-diff[1]: This flexible command does much more than - we've seen in the few examples above. - * gitlink:git-format-patch[1], gitlink:git-am[1]: These convert series of git commits into emailed patches, and vice versa, useful for projects such as the linux kernel which rely heavily