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+git-p4 - Perforce <-> Git converter using git-fast-import
+
+Usage
+=====
+
+git-p4 can be used in two different ways:
+
+1) To import changes from Perforce to a Git repository, using "git-p4 sync".
+
+2) To submit changes from Git back to Perforce, using "git-p4 submit".
+
+Importing
+=========
+
+Simply start with
+
+  git-p4 clone //depot/path/project
+
+or
+
+  git-p4 clone //depot/path/project myproject
+
+This will:
+
+1) Create an empty git repository in a subdirectory called "project" (or
+"myproject" with the second command)
+
+2) Import the head revision from the given Perforce path into a git branch
+called "p4" (remotes/p4 actually)
+
+3) Create a master branch based on it and check it out.
+
+If you want the entire history (not just the head revision) then you can simply
+append a "@all" to the depot path:
+
+  git-p4 clone //depot/project/main@all myproject
+
+
+
+If you want more control you can also use the git-p4 sync command directly:
+
+  mkdir repo-git
+  cd repo-git
+  git init
+  git-p4 sync //path/in/your/perforce/depot
+
+This will import the current head revision of the specified depot path into a
+"remotes/p4/master" branch of your git repository. You can use the
+--branch=mybranch option to import into a different branch.
+
+If you want to import the entire history of a given depot path simply use:
+
+  git-p4 sync //path/in/depot@all
+
+
+Note:
+
+To achieve optimal compression you may want to run 'git repack -a -d -f' after
+a big import. This may take a while.
+
+Incremental Imports
+===================
+
+After an initial import you can continue to synchronize your git repository
+with newer changes from the Perforce depot by just calling
+
+  git-p4 sync
+
+in your git repository. By default the "remotes/p4/master" branch is updated.
+
+Advanced Setup
+==============
+
+Suppose you have a periodically updated git repository somewhere, containing a
+complete import of a Perforce project. This repository can be cloned and used
+with git-p4. When updating the cloned repository with the "sync" command,
+git-p4 will try to fetch changes from the original repository first. The git
+protocol used with this is usually faster than importing from Perforce
+directly.
+
+This behaviour can be disabled by setting the "git-p4.syncFromOrigin" git
+configuration variable to "false".
+
+Updating
+========
+
+A common working pattern is to fetch the latest changes from the Perforce depot
+and merge them with local uncommitted changes. The recommended way is to use
+git's rebase mechanism to preserve linear history. git-p4 provides a convenient
+
+  git-p4 rebase
+
+command that calls git-p4 sync followed by git rebase to rebase the current
+working branch.
+
+Submitting
+==========
+
+git-p4 has support for submitting changes from a git repository back to the
+Perforce depot. This requires a Perforce checkout separate from your git
+repository. To submit all changes that are in the current git branch but not in
+the "p4" branch (or "origin" if "p4" doesn't exist) simply call
+
+    git-p4 submit
+
+in your git repository. If you want to submit changes in a specific branch that
+is not your current git branch you can also pass that as an argument:
+
+    git-p4 submit mytopicbranch
+
+You can override the reference branch with the --origin=mysourcebranch option.
+
+If a submit fails you may have to "p4 resolve" and submit manually. You can
+continue importing the remaining changes with
+
+  git-p4 submit --continue
+
+Example
+=======
+
+# Clone a repository
+  git-p4 clone //depot/path/project
+# Enter the newly cloned directory
+  cd project
+# Do some work...
+  vi foo.h
+# ... and commit locally to gi
+  git commit foo.h
+# In the meantime somebody submitted changes to the Perforce depot. Rebase your latest
+# changes against the latest changes in Perforce:
+  git-p4 rebase
+# Submit your locally committed changes back to Perforce
+  git-p4 submit
+# ... and synchronize with Perforce
+  git-p4 rebase
+
+
+Configuration parameters
+========================
+
+git-p4.user ($P4USER)
+
+Allows you to specify the username to use to connect to the Perforce repository.
+
+  git config [--global] git-p4.user public
+
+git-p4.password ($P4PASS)
+
+Allows you to specify the password to use to connect to the Perforce repository.
+Warning this password will be visible on the command-line invocation of the p4 binary.
+
+  git config [--global] git-p4.password public1234
+
+git-p4.port ($P4PORT)
+
+Specify the port to be used to contact the Perforce server. As this will be passed
+directly to the p4 binary, it may be in the format host:port as well.
+
+  git config [--global] git-p4.port codes.zimbra.com:2666
+
+git-p4.host ($P4HOST)
+
+Specify the host to contact for a Perforce repository.
+
+  git config [--global] git-p4.host perforce.example.com
+
+git-p4.client ($P4CLIENT)
+
+Specify the client name to use
+
+  git config [--global] git-p4.client public-view
+
+git-p4.allowSubmit
+
+  git config [--global] git-p4.allowSubmit false
+
+git-p4.syncFromOrigin
+
+A useful setup may be that you have a periodically updated git repository
+somewhere that contains a complete import of a Perforce project. That git
+repository can be used to clone the working repository from and one would
+import from Perforce directly after cloning using git-p4. If the connection to
+the Perforce server is slow and the working repository hasn't been synced for a
+while it may be desirable to fetch changes from the origin git repository using
+the efficient git protocol. git-p4 supports this setup by calling "git fetch origin"
+by default if there is an origin branch. You can disable this using:
+
+  git config [--global] git-p4.syncFromOrigin false
+
+git-p4.useclientspec
+
+  git config [--global] git-p4.useclientspec false
+
+Implementation Details...
+=========================
+
+* Changesets from Perforce are imported using git fast-import.
+* The import does not require anything from the Perforce client view as it just uses
+  "p4 print //depot/path/file#revision" to get the actual file contents.
+* Every imported changeset has a special [git-p4...] line at the
+  end of the log message that gives information about the corresponding
+  Perforce change number and is also used by git-p4 itself to find out
+  where to continue importing when doing incremental imports.
+  Basically when syncing it extracts the perforce change number of the
+  latest commit in the "p4" branch and uses "p4 changes //depot/path/...@changenum,#head"
+  to find out which changes need to be imported.
+* git-p4 submit uses "git rev-list" to pick the commits between the "p4" branch
+  and the current branch.
+  The commits themselves are applied using git diff/format-patch ... | git apply
+