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git-fast-import(1)                 Git Manual                 git-fast-import(1)




NAME

       git-fast-import - Backend for fast Git data importers


SYNOPSIS

       frontend | git fast-import [<options>]



DESCRIPTION

       This program is usually not what the end user wants to run directly. Most
       end users want to use one of the existing frontend programs, which parses
       a specific type of foreign source and feeds the contents stored there to
       git fast-import.

       fast-import reads a mixed command/data stream from standard input and
       writes one or more packfiles directly into the current repository. When
       EOF is received on standard input, fast import writes out updated branch
       and tag refs, fully updating the current repository with the newly
       imported data.

       The fast-import backend itself can import into an empty repository (one
       that has already been initialized by git init) or incrementally update an
       existing populated repository. Whether or not incremental imports are
       supported from a particular foreign source depends on the frontend
       program in use.


OPTIONS

       --force
           Force updating modified existing branches, even if doing so would
           cause commits to be lost (as the new commit does not contain the old
           commit).

       --quiet
           Disable the output shown by --stats, making fast-import usually be
           silent when it is successful. However, if the import stream has
           directives intended to show user output (e.g.  progress directives),
           the corresponding messages will still be shown.

       --stats
           Display some basic statistics about the objects fast-import has
           created, the packfiles they were stored into, and the memory used by
           fast-import during this run. Showing this output is currently the
           default, but can be disabled with --quiet.

       --allow-unsafe-features
           Many command-line options can be provided as part of the fast-import
           stream itself by using the feature or option commands. However, some
           of these options are unsafe (e.g., allowing fast-import to access the
           filesystem outside of the repository). These options are disabled by
           default, but can be allowed by providing this option on the command
           line. This currently impacts only the export-marks, import-marks, and
           import-marks-if-exists feature commands.

               Only enable this option if you trust the program generating the
               fast-import stream! This option is enabled automatically for
               remote-helpers that use the `import` capability, as they are
               already trusted to run their own code.

   Options for Frontends
       --cat-blob-fd=<fd>
           Write responses to get-mark, cat-blob, and ls queries to the file
           descriptor <fd> instead of stdout. Allows progress output intended
           for the end-user to be separated from other output.

       --date-format=<fmt>
           Specify the type of dates the frontend will supply to fast-import
           within author, committer and tagger commands. See "Date Formats"
           below for details about which formats are supported, and their
           syntax.

       --done
           Terminate with error if there is no done command at the end of the
           stream. This option might be useful for detecting errors that cause
           the frontend to terminate before it has started to write a stream.

   Locations of Marks Files
       --export-marks=<file>
           Dumps the internal marks table to <file> when complete. Marks are
           written one per line as :markid SHA-1. Frontends can use this file to
           validate imports after they have been completed, or to save the marks
           table across incremental runs. As <file> is only opened and truncated
           at checkpoint (or completion) the same path can also be safely given
           to --import-marks.

       --import-marks=<file>
           Before processing any input, load the marks specified in <file>. The
           input file must exist, must be readable, and must use the same format
           as produced by --export-marks. Multiple options may be supplied to
           import more than one set of marks. If a mark is defined to different
           values, the last file wins.

       --import-marks-if-exists=<file>
           Like --import-marks but instead of erroring out, silently skips the
           file if it does not exist.

       --[no-]relative-marks
           After specifying --relative-marks the paths specified with
           --import-marks= and --export-marks= are relative to an internal
           directory in the current repository. In git-fast-import this means
           that the paths are relative to the .git/info/fast-import directory.
           However, other importers may use a different location.

           Relative and non-relative marks may be combined by interweaving
           --(no-)-relative-marks with the --(import|export)-marks= options.

   Submodule Rewriting
       --rewrite-submodules-from=<name>:<file>,
       --rewrite-submodules-to=<name>:<file>
           Rewrite the object IDs for the submodule specified by <name> from the
           values used in the from <file> to those used in the to <file>. The
           from marks should have been created by git fast-export, and the to
           marks should have been created by git fast-import when importing that
           same submodule.

           <name> may be any arbitrary string not containing a colon character,
           but the same value must be used with both options when specifying
           corresponding marks. Multiple submodules may be specified with
           different values for <name>. It is an error not to use these options
           in corresponding pairs.

           These options are primarily useful when converting a repository from
           one hash algorithm to another; without them, fast-import will fail if
           it encounters a submodule because it has no way of writing the object
           ID into the new hash algorithm.

   Performance and Compression Tuning
       --active-branches=<n>
           Maximum number of branches to maintain active at once. See "Memory
           Utilization" below for details. Default is 5.

       --big-file-threshold=<n>
           Maximum size of a blob that fast-import will attempt to create a
           delta for, expressed in bytes. The default is 512m (512 MiB). Some
           importers may wish to lower this on systems with constrained memory.

       --depth=<n>
           Maximum delta depth, for blob and tree deltification. Default is 50.

       --export-pack-edges=<file>
           After creating a packfile, print a line of data to <file> listing the
           filename of the packfile and the last commit on each branch that was
           written to that packfile. This information may be useful after
           importing projects whose total object set exceeds the 4 GiB packfile
           limit, as these commits can be used as edge points during calls to
           git pack-objects.

       --max-pack-size=<n>
           Maximum size of each output packfile. The default is unlimited.

       fastimport.unpackLimit
           See git-config(1)


PERFORMANCE

       The design of fast-import allows it to import large projects in a minimum
       amount of memory usage and processing time. Assuming the frontend is able
       to keep up with fast-import and feed it a constant stream of data, import
       times for projects holding 10+ years of history and containing 100,000+
       individual commits are generally completed in just 1-2 hours on quite
       modest (~$2,000 USD) hardware.

       Most bottlenecks appear to be in foreign source data access (the source
       just cannot extract revisions fast enough) or disk IO (fast-import writes
       as fast as the disk will take the data). Imports will run faster if the
       source data is stored on a different drive than the destination Git
       repository (due to less IO contention).


DEVELOPMENT COST

       A typical frontend for fast-import tends to weigh in at approximately 200
       lines of Perl/Python/Ruby code. Most developers have been able to create
       working importers in just a couple of hours, even though it is their
       first exposure to fast-import, and sometimes even to Git. This is an
       ideal situation, given that most conversion tools are throw-away (use
       once, and never look back).


PARALLEL OPERATION

       Like git push or git fetch, imports handled by fast-import are safe to
       run alongside parallel git repack -a -d or git gc invocations, or any
       other Git operation (including git prune, as loose objects are never used
       by fast-import).

       fast-import does not lock the branch or tag refs it is actively
       importing. After the import, during its ref update phase, fast-import
       tests each existing branch ref to verify the update will be a
       fast-forward update (the commit stored in the ref is contained in the new
       history of the commit to be written). If the update is not a fast-forward
       update, fast-import will skip updating that ref and instead prints a
       warning message. fast-import will always attempt to update all branch
       refs, and does not stop on the first failure.

       Branch updates can be forced with --force, but it's recommended that this
       only be used on an otherwise quiet repository. Using --force is not
       necessary for an initial import into an empty repository.


TECHNICAL DISCUSSION

       fast-import tracks a set of branches in memory. Any branch can be created
       or modified at any point during the import process by sending a commit
       command on the input stream. This design allows a frontend program to
       process an unlimited number of branches simultaneously, generating
       commits in the order they are available from the source data. It also
       simplifies the frontend programs considerably.

       fast-import does not use or alter the current working directory, or any
       file within it. (It does however update the current Git repository, as
       referenced by GIT_DIR.) Therefore an import frontend may use the working
       directory for its own purposes, such as extracting file revisions from
       the foreign source. This ignorance of the working directory also allows
       fast-import to run very quickly, as it does not need to perform any
       costly file update operations when switching between branches.


INPUT FORMAT

       With the exception of raw file data (which Git does not interpret) the
       fast-import input format is text (ASCII) based. This text based format
       simplifies development and debugging of frontend programs, especially
       when a higher level language such as Perl, Python or Ruby is being used.

       fast-import is very strict about its input. Where we say SP below we mean
       exactly one space. Likewise LF means one (and only one) linefeed and HT
       one (and only one) horizontal tab. Supplying additional whitespace
       characters will cause unexpected results, such as branch names or file
       names with leading or trailing spaces in their name, or early termination
       of fast-import when it encounters unexpected input.

   Stream Comments
       To aid in debugging frontends fast-import ignores any line that begins
       with # (ASCII pound/hash) up to and including the line ending LF. A
       comment line may contain any sequence of bytes that does not contain an
       LF and therefore may be used to include any detailed debugging
       information that might be specific to the frontend and useful when
       inspecting a fast-import data stream.

   Date Formats
       The following date formats are supported. A frontend should select the
       format it will use for this import by passing the format name in the
       --date-format=<fmt> command-line option.

       raw
           This is the Git native format and is <time> SP <offutc>. It is also
           fast-import's default format, if --date-format was not specified.

           The time of the event is specified by <time> as the number of seconds
           since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is written as
           an ASCII decimal integer.

           The local offset is specified by <offutc> as a positive or negative
           offset from UTC. For example EST (which is 5 hours behind UTC) would
           be expressed in <tz> by "-0500" while UTC is "+0000". The local
           offset does not affect <time>; it is used only as an advisement to
           help formatting routines display the timestamp.

           If the local offset is not available in the source material, use
           "+0000", or the most common local offset. For example many
           organizations have a CVS repository which has only ever been accessed
           by users who are located in the same location and time zone. In this
           case a reasonable offset from UTC could be assumed.

           Unlike the rfc2822 format, this format is very strict. Any variation
           in formatting will cause fast-import to reject the value, and some
           sanity checks on the numeric values may also be performed.

       raw-permissive
           This is the same as raw except that no sanity checks on the numeric
           epoch and local offset are performed. This can be useful when trying
           to filter or import an existing history with e.g. bogus timezone
           values.

       rfc2822
           This is the standard email format as described by RFC 2822.

           An example value is "Tue Feb 6 11:22:18 2007 -0500". The Git parser
           is accurate, but a little on the lenient side. It is the same parser
           used by git am when applying patches received from email.

           Some malformed strings may be accepted as valid dates. In some of
           these cases Git will still be able to obtain the correct date from
           the malformed string. There are also some types of malformed strings
           which Git will parse wrong, and yet consider valid. Seriously
           malformed strings will be rejected.

           Unlike the raw format above, the time zone/UTC offset information
           contained in an RFC 2822 date string is used to adjust the date value
           to UTC prior to storage. Therefore it is important that this
           information be as accurate as possible.

           If the source material uses RFC 2822 style dates, the frontend should
           let fast-import handle the parsing and conversion (rather than
           attempting to do it itself) as the Git parser has been well tested in
           the wild.

           Frontends should prefer the raw format if the source material already
           uses UNIX-epoch format, can be coaxed to give dates in that format,
           or its format is easily convertible to it, as there is no ambiguity
           in parsing.

       now
           Always use the current time and time zone. The literal now must
           always be supplied for <when>.

           This is a toy format. The current time and time zone of this system
           is always copied into the identity string at the time it is being
           created by fast-import. There is no way to specify a different time
           or time zone.

           This particular format is supplied as it's short to implement and may
           be useful to a process that wants to create a new commit right now,
           without needing to use a working directory or git update-index.

           If separate author and committer commands are used in a commit the
           timestamps may not match, as the system clock will be polled twice
           (once for each command). The only way to ensure that both author and
           committer identity information has the same timestamp is to omit
           author (thus copying from committer) or to use a date format other
           than now.

   Commands
       fast-import accepts several commands to update the current repository and
       control the current import process. More detailed discussion (with
       examples) of each command follows later.

       commit
           Creates a new branch or updates an existing branch by creating a new
           commit and updating the branch to point at the newly created commit.

       tag
           Creates an annotated tag object from an existing commit or branch.
           Lightweight tags are not supported by this command, as they are not
           recommended for recording meaningful points in time.

       reset
           Reset an existing branch (or a new branch) to a specific revision.
           This command must be used to change a branch to a specific revision
           without making a commit on it.

       blob
           Convert raw file data into a blob, for future use in a commit
           command. This command is optional and is not needed to perform an
           import.

       alias
           Record that a mark refers to a given object without first creating
           any new object. Using --import-marks and referring to missing marks
           will cause fast-import to fail, so aliases can provide a way to set
           otherwise pruned commits to a valid value (e.g. the nearest
           non-pruned ancestor).

       checkpoint
           Forces fast-import to close the current packfile, generate its unique
           SHA-1 checksum and index, and start a new packfile. This command is
           optional and is not needed to perform an import.

       progress
           Causes fast-import to echo the entire line to its own standard
           output. This command is optional and is not needed to perform an
           import.

       done
           Marks the end of the stream. This command is optional unless the done
           feature was requested using the --done command-line option or feature
           done command.

       get-mark
           Causes fast-import to print the SHA-1 corresponding to a mark to the
           file descriptor set with --cat-blob-fd, or stdout if unspecified.

       cat-blob
           Causes fast-import to print a blob in cat-file --batch format to the
           file descriptor set with --cat-blob-fd or stdout if unspecified.

       ls
           Causes fast-import to print a line describing a directory entry in
           ls-tree format to the file descriptor set with --cat-blob-fd or
           stdout if unspecified.

       feature
           Enable the specified feature. This requires that fast-import supports
           the specified feature, and aborts if it does not.

       option
           Specify any of the options listed under OPTIONS that do not change
           stream semantic to suit the frontend's needs. This command is
           optional and is not needed to perform an import.

   commit
       Create or update a branch with a new commit, recording one logical change
       to the project.

                   'commit' SP <ref> LF
                   mark?
                   original-oid?
                   ('author' (SP <name>)? SP LT <email> GT SP <when> LF)?
                   'committer' (SP <name>)? SP LT <email> GT SP <when> LF
                   ('encoding' SP <encoding>)?
                   data
                   ('from' SP <commit-ish> LF)?
                   ('merge' SP <commit-ish> LF)*
                   (filemodify | filedelete | filecopy | filerename | filedeleteall | notemodify)*
                   LF?

       where <ref> is the name of the branch to make the commit on. Typically
       branch names are prefixed with refs/heads/ in Git, so importing the CVS
       branch symbol RELENG-1_0 would use refs/heads/RELENG-1_0 for the value of
       <ref>. The value of <ref> must be a valid refname in Git. As LF is not
       valid in a Git refname, no quoting or escaping syntax is supported here.

       A mark command may optionally appear, requesting fast-import to save a
       reference to the newly created commit for future use by the frontend (see
       below for format). It is very common for frontends to mark every commit
       they create, thereby allowing future branch creation from any imported
       commit.

       The data command following committer must supply the commit message (see
       below for data command syntax). To import an empty commit message use a 0
       length data. Commit messages are free-form and are not interpreted by
       Git. Currently they must be encoded in UTF-8, as fast-import does not
       permit other encodings to be specified.

       Zero or more filemodify, filedelete, filecopy, filerename, filedeleteall
       and notemodify commands may be included to update the contents of the
       branch prior to creating the commit. These commands may be supplied in
       any order. However it is recommended that a filedeleteall command precede
       all filemodify, filecopy, filerename and notemodify commands in the same
       commit, as filedeleteall wipes the branch clean (see below).

       The LF after the command is optional (it used to be required). Note that
       for reasons of backward compatibility, if the commit ends with a data
       command (i.e. it has no from, merge, filemodify, filedelete, filecopy,
       filerename, filedeleteall or notemodify commands) then two LF commands
       may appear at the end of the command instead of just one.

       author

           An author command may optionally appear, if the author information
           might differ from the committer information. If author is omitted
           then fast-import will automatically use the committer's information
           for the author portion of the commit. See below for a description of
           the fields in author, as they are identical to committer.

       committer

           The committer command indicates who made this commit, and when they
           made it.

           Here <name> is the person's display name (for example "Com M Itter")
           and <email> is the person's email address ("cm@example.com"). LT and
           GT are the literal less-than (\x3c) and greater-than (\x3e) symbols.
           These are required to delimit the email address from the other fields
           in the line. Note that <name> and <email> are free-form and may
           contain any sequence of bytes, except LT, GT and LF. <name> is
           typically UTF-8 encoded.

           The time of the change is specified by <when> using the date format
           that was selected by the --date-format=<fmt> command-line option. See
           "Date Formats" above for the set of supported formats, and their
           syntax.

       encoding

           The optional encoding command indicates the encoding of the commit
           message. Most commits are UTF-8 and the encoding is omitted, but this
           allows importing commit messages into git without first reencoding
           them.

       from

           The from command is used to specify the commit to initialize this
           branch from. This revision will be the first ancestor of the new
           commit. The state of the tree built at this commit will begin with
           the state at the from commit, and be altered by the content
           modifications in this commit.

           Omitting the from command in the first commit of a new branch will
           cause fast-import to create that commit with no ancestor. This tends
           to be desired only for the initial commit of a project. If the
           frontend creates all files from scratch when making a new branch, a
           merge command may be used instead of from to start the commit with an
           empty tree. Omitting the from command on existing branches is usually
           desired, as the current commit on that branch is automatically
           assumed to be the first ancestor of the new commit.

           As LF is not valid in a Git refname or SHA-1 expression, no quoting
           or escaping syntax is supported within <commit-ish>.

           Here <commit-ish> is any of the following:

           o   The name of an existing branch already in fast-import's internal
               branch table. If fast-import doesn't know the name, it's treated
               as a SHA-1 expression.

           o   A mark reference, :<idnum>, where <idnum> is the mark number.

               The reason fast-import uses : to denote a mark reference is this
               character is not legal in a Git branch name. The leading : makes
               it easy to distinguish between the mark 42 (:42) and the branch
               42 (42 or refs/heads/42), or an abbreviated SHA-1 which happened
               to consist only of base-10 digits.

               Marks must be declared (via mark) before they can be used.

           o   A complete 40 byte or abbreviated commit SHA-1 in hex.

           o   Any valid Git SHA-1 expression that resolves to a commit. See
               "SPECIFYING REVISIONS" in gitrevisions(7) for details.

           o   The special null SHA-1 (40 zeros) specifies that the branch is to
               be removed.

           The special case of restarting an incremental import from the current
           branch value should be written as:

                       from refs/heads/branch^0


           The ^0 suffix is necessary as fast-import does not permit a branch to
           start from itself, and the branch is created in memory before the
           from command is even read from the input. Adding ^0 will force
           fast-import to resolve the commit through Git's revision parsing
           library, rather than its internal branch table, thereby loading in
           the existing value of the branch.

       merge

           Includes one additional ancestor commit. The additional ancestry link
           does not change the way the tree state is built at this commit. If
           the from command is omitted when creating a new branch, the first
           merge commit will be the first ancestor of the current commit, and
           the branch will start out with no files. An unlimited number of merge
           commands per commit are permitted by fast-import, thereby
           establishing an n-way merge.

           Here <commit-ish> is any of the commit specification expressions also
           accepted by from (see above).

       filemodify

           Included in a commit command to add a new file or change the content
           of an existing file. This command has two different means of
           specifying the content of the file.

           External data format
               The data content for the file was already supplied by a prior
               blob command. The frontend just needs to connect it.

                           'M' SP <mode> SP <dataref> SP <path> LF

               Here usually <dataref> must be either a mark reference (:<idnum>)
               set by a prior blob command, or a full 40-byte SHA-1 of an
               existing Git blob object. If <mode> is 040000` then <dataref>
               must be the full 40-byte SHA-1 of an existing Git tree object or
               a mark reference set with --import-marks.

           Inline data format
               The data content for the file has not been supplied yet. The
               frontend wants to supply it as part of this modify command.

                           'M' SP <mode> SP 'inline' SP <path> LF
                           data

               See below for a detailed description of the data command.

           In both formats <mode> is the type of file entry, specified in octal.
           Git only supports the following modes:

           o   100644 or 644: A normal (not-executable) file. The majority of
               files in most projects use this mode. If in doubt, this is what
               you want.

           o   100755 or 755: A normal, but executable, file.

           o   120000: A symlink, the content of the file will be the link
               target.

           o   160000: A gitlink, SHA-1 of the object refers to a commit in
               another repository. Git links can only be specified by SHA or
               through a commit mark. They are used to implement submodules.

           o   040000: A subdirectory. Subdirectories can only be specified by
               SHA or through a tree mark set with --import-marks.

           In both formats <path> is the complete path of the file to be added
           (if not already existing) or modified (if already existing).

           A <path> string must use UNIX-style directory separators (forward
           slash /), may contain any byte other than LF, and must not start with
           double quote (").

           A path can use C-style string quoting; this is accepted in all cases
           and mandatory if the filename starts with double quote or contains
           LF. In C-style quoting, the complete name should be surrounded with
           double quotes, and any LF, backslash, or double quote characters must
           be escaped by preceding them with a backslash (e.g., "path/with\n, \\
           and \" in it").

           The value of <path> must be in canonical form. That is it must not:

           o   contain an empty directory component (e.g.  foo//bar is invalid),

           o   end with a directory separator (e.g.  foo/ is invalid),

           o   start with a directory separator (e.g.  /foo is invalid),

           o   contain the special component . or .. (e.g.  foo/./bar and
               foo/../bar are invalid).

           The root of the tree can be represented by an empty string as <path>.

           It is recommended that <path> always be encoded using UTF-8.

       filedelete

           Included in a commit command to remove a file or recursively delete
           an entire directory from the branch. If the file or directory removal
           makes its parent directory empty, the parent directory will be
           automatically removed too. This cascades up the tree until the first
           non-empty directory or the root is reached.

                       'D' SP <path> LF

           here <path> is the complete path of the file or subdirectory to be
           removed from the branch. See filemodify above for a detailed
           description of <path>.

       filecopy

           Recursively copies an existing file or subdirectory to a different
           location within the branch. The existing file or directory must
           exist. If the destination exists it will be completely replaced by
           the content copied from the source.

                       'C' SP <path> SP <path> LF

           here the first <path> is the source location and the second <path> is
           the destination. See filemodify above for a detailed description of
           what <path> may look like. To use a source path that contains SP the
           path must be quoted.

           A filecopy command takes effect immediately. Once the source location
           has been copied to the destination any future commands applied to the
           source location will not impact the destination of the copy.

       filerename

           Renames an existing file or subdirectory to a different location
           within the branch. The existing file or directory must exist. If the
           destination exists it will be replaced by the source directory.

                       'R' SP <path> SP <path> LF

           here the first <path> is the source location and the second <path> is
           the destination. See filemodify above for a detailed description of
           what <path> may look like. To use a source path that contains SP the
           path must be quoted.

           A filerename command takes effect immediately. Once the source
           location has been renamed to the destination any future commands
           applied to the source location will create new files there and not
           impact the destination of the rename.

           Note that a filerename is the same as a filecopy followed by a
           filedelete of the source location. There is a slight performance
           advantage to using filerename, but the advantage is so small that it
           is never worth trying to convert a delete/add pair in source material
           into a rename for fast-import. This filerename command is provided
           just to simplify frontends that already have rename information and
           don't want bother with decomposing it into a filecopy followed by a
           filedelete.

       filedeleteall

           Included in a commit command to remove all files (and also all
           directories) from the branch. This command resets the internal branch
           structure to have no files in it, allowing the frontend to
           subsequently add all interesting files from scratch.

                       'deleteall' LF

           This command is extremely useful if the frontend does not know (or
           does not care to know) what files are currently on the branch, and
           therefore cannot generate the proper filedelete commands to update
           the content.

           Issuing a filedeleteall followed by the needed filemodify commands to
           set the correct content will produce the same results as sending only
           the needed filemodify and filedelete commands. The filedeleteall
           approach may however require fast-import to use slightly more memory
           per active branch (less than 1 MiB for even most large projects); so
           frontends that can easily obtain only the affected paths for a commit
           are encouraged to do so.

       notemodify

           Included in a commit <notes_ref> command to add a new note annotating
           a <commit-ish> or change this annotation contents. Internally it is
           similar to filemodify 100644 on <commit-ish> path (maybe split into
           subdirectories). It's not advised to use any other commands to write
           to the <notes_ref> tree except filedeleteall to delete all existing
           notes in this tree. This command has two different means of
           specifying the content of the note.

           External data format
               The data content for the note was already supplied by a prior
               blob command. The frontend just needs to connect it to the commit
               that is to be annotated.

                           'N' SP <dataref> SP <commit-ish> LF

               Here <dataref> can be either a mark reference (:<idnum>) set by a
               prior blob command, or a full 40-byte SHA-1 of an existing Git
               blob object.

           Inline data format
               The data content for the note has not been supplied yet. The
               frontend wants to supply it as part of this modify command.

                           'N' SP 'inline' SP <commit-ish> LF
                           data

               See below for a detailed description of the data command.

           In both formats <commit-ish> is any of the commit specification
           expressions also accepted by from (see above).

   mark
       Arranges for fast-import to save a reference to the current object,
       allowing the frontend to recall this object at a future point in time,
       without knowing its SHA-1. Here the current object is the object creation
       command the mark command appears within. This can be commit, tag, and
       blob, but commit is the most common usage.

                   'mark' SP ':' <idnum> LF

       where <idnum> is the number assigned by the frontend to this mark. The
       value of <idnum> is expressed as an ASCII decimal integer. The value 0 is
       reserved and cannot be used as a mark. Only values greater than or equal
       to 1 may be used as marks.

       New marks are created automatically. Existing marks can be moved to
       another object simply by reusing the same <idnum> in another mark
       command.

   original-oid
       Provides the name of the object in the original source control system.
       fast-import will simply ignore this directive, but filter processes which
       operate on and modify the stream before feeding to fast-import may have
       uses for this information

                   'original-oid' SP <object-identifier> LF

       where <object-identifier> is any string not containing LF.

   tag
       Creates an annotated tag referring to a specific commit. To create
       lightweight (non-annotated) tags see the reset command below.

                   'tag' SP <name> LF
                   mark?
                   'from' SP <commit-ish> LF
                   original-oid?
                   'tagger' (SP <name>)? SP LT <email> GT SP <when> LF
                   data

       where <name> is the name of the tag to create.

       Tag names are automatically prefixed with refs/tags/ when stored in Git,
       so importing the CVS branch symbol RELENG-1_0-FINAL would use just
       RELENG-1_0-FINAL for <name>, and fast-import will write the corresponding
       ref as refs/tags/RELENG-1_0-FINAL.

       The value of <name> must be a valid refname in Git and therefore may
       contain forward slashes. As LF is not valid in a Git refname, no quoting
       or escaping syntax is supported here.

       The from command is the same as in the commit command; see above for
       details.

       The tagger command uses the same format as committer within commit; again
       see above for details.

       The data command following tagger must supply the annotated tag message
       (see below for data command syntax). To import an empty tag message use a
       0 length data. Tag messages are free-form and are not interpreted by Git.
       Currently they must be encoded in UTF-8, as fast-import does not permit
       other encodings to be specified.

       Signing annotated tags during import from within fast-import is not
       supported. Trying to include your own PGP/GPG signature is not
       recommended, as the frontend does not (easily) have access to the
       complete set of bytes which normally goes into such a signature. If
       signing is required, create lightweight tags from within fast-import with
       reset, then create the annotated versions of those tags offline with the
       standard git tag process.

   reset
       Creates (or recreates) the named branch, optionally starting from a
       specific revision. The reset command allows a frontend to issue a new
       from command for an existing branch, or to create a new branch from an
       existing commit without creating a new commit.

                   'reset' SP <ref> LF
                   ('from' SP <commit-ish> LF)?
                   LF?

       For a detailed description of <ref> and <commit-ish> see above under
       commit and from.

       The LF after the command is optional (it used to be required).

       The reset command can also be used to create lightweight (non-annotated)
       tags. For example:

           reset refs/tags/938
           from :938

       would create the lightweight tag refs/tags/938 referring to whatever
       commit mark :938 references.

   blob
       Requests writing one file revision to the packfile. The revision is not
       connected to any commit; this connection must be formed in a subsequent
       commit command by referencing the blob through an assigned mark.

                   'blob' LF
                   mark?
                   original-oid?
                   data

       The mark command is optional here as some frontends have chosen to
       generate the Git SHA-1 for the blob on their own, and feed that directly
       to commit. This is typically more work than it's worth however, as marks
       are inexpensive to store and easy to use.

   data
       Supplies raw data (for use as blob/file content, commit messages, or
       annotated tag messages) to fast-import. Data can be supplied using an
       exact byte count or delimited with a terminating line. Real frontends
       intended for production-quality conversions should always use the exact
       byte count format, as it is more robust and performs better. The
       delimited format is intended primarily for testing fast-import.

       Comment lines appearing within the <raw> part of data commands are always
       taken to be part of the body of the data and are therefore never ignored
       by fast-import. This makes it safe to import any file/message content
       whose lines might start with #.

       Exact byte count format
           The frontend must specify the number of bytes of data.

                       'data' SP <count> LF
                       <raw> LF?

           where <count> is the exact number of bytes appearing within <raw>.
           The value of <count> is expressed as an ASCII decimal integer. The LF
           on either side of <raw> is not included in <count> and will not be
           included in the imported data.

           The LF after <raw> is optional (it used to be required) but
           recommended. Always including it makes debugging a fast-import stream
           easier as the next command always starts in column 0 of the next
           line, even if <raw> did not end with an LF.

       Delimited format
           A delimiter string is used to mark the end of the data. fast-import
           will compute the length by searching for the delimiter. This format
           is primarily useful for testing and is not recommended for real data.

                       'data' SP '<<' <delim> LF
                       <raw> LF
                       <delim> LF
                       LF?

           where <delim> is the chosen delimiter string. The string <delim> must
           not appear on a line by itself within <raw>, as otherwise fast-import
           will think the data ends earlier than it really does. The LF
           immediately trailing <raw> is part of <raw>. This is one of the
           limitations of the delimited format, it is impossible to supply a
           data chunk which does not have an LF as its last byte.

           The LF after <delim> LF is optional (it used to be required).

   alias
       Record that a mark refers to a given object without first creating any
       new object.

                   'alias' LF
                   mark
                   'to' SP <commit-ish> LF
                   LF?

       For a detailed description of <commit-ish> see above under from.

   checkpoint
       Forces fast-import to close the current packfile, start a new one, and to
       save out all current branch refs, tags and marks.

                   'checkpoint' LF
                   LF?

       Note that fast-import automatically switches packfiles when the current
       packfile reaches --max-pack-size, or 4 GiB, whichever limit is smaller.
       During an automatic packfile switch fast-import does not update the
       branch refs, tags or marks.

       As a checkpoint can require a significant amount of CPU time and disk IO
       (to compute the overall pack SHA-1 checksum, generate the corresponding
       index file, and update the refs) it can easily take several minutes for a
       single checkpoint command to complete.

       Frontends may choose to issue checkpoints during extremely large and long
       running imports, or when they need to allow another Git process access to
       a branch. However given that a 30 GiB Subversion repository can be loaded
       into Git through fast-import in about 3 hours, explicit checkpointing may
       not be necessary.

       The LF after the command is optional (it used to be required).

   progress
       Causes fast-import to print the entire progress line unmodified to its
       standard output channel (file descriptor 1) when the command is processed
       from the input stream. The command otherwise has no impact on the current
       import, or on any of fast-import's internal state.

                   'progress' SP <any> LF
                   LF?

       The <any> part of the command may contain any sequence of bytes that does
       not contain LF. The LF after the command is optional. Callers may wish to
       process the output through a tool such as sed to remove the leading part
       of the line, for example:

           frontend | git fast-import | sed 's/^progress //'

       Placing a progress command immediately after a checkpoint will inform the
       reader when the checkpoint has been completed and it can safely access
       the refs that fast-import updated.

   get-mark
       Causes fast-import to print the SHA-1 corresponding to a mark to stdout
       or to the file descriptor previously arranged with the --cat-blob-fd
       argument. The command otherwise has no impact on the current import; its
       purpose is to retrieve SHA-1s that later commits might want to refer to
       in their commit messages.

                   'get-mark' SP ':' <idnum> LF

       See "Responses To Commands" below for details about how to read this
       output safely.

   cat-blob
       Causes fast-import to print a blob to a file descriptor previously
       arranged with the --cat-blob-fd argument. The command otherwise has no
       impact on the current import; its main purpose is to retrieve blobs that
       may be in fast-import's memory but not accessible from the target
       repository.

                   'cat-blob' SP <dataref> LF

       The <dataref> can be either a mark reference (:<idnum>) set previously or
       a full 40-byte SHA-1 of a Git blob, preexisting or ready to be written.

       Output uses the same format as git cat-file --batch:

           <sha1> SP 'blob' SP <size> LF
           <contents> LF

       This command can be used where a filemodify directive can appear,
       allowing it to be used in the middle of a commit. For a filemodify using
       an inline directive, it can also appear right before the data directive.

       See "Responses To Commands" below for details about how to read this
       output safely.

   ls
       Prints information about the object at a path to a file descriptor
       previously arranged with the --cat-blob-fd argument. This allows printing
       a blob from the active commit (with cat-blob) or copying a blob or tree
       from a previous commit for use in the current one (with filemodify).

       The ls command can also be used where a filemodify directive can appear,
       allowing it to be used in the middle of a commit.

       Reading from the active commit
           This form can only be used in the middle of a commit. The path names
           a directory entry within fast-import's active commit. The path must
           be quoted in this case.

                       'ls' SP <path> LF

       Reading from a named tree
           The <dataref> can be a mark reference (:<idnum>) or the full 40-byte
           SHA-1 of a Git tag, commit, or tree object, preexisting or waiting to
           be written. The path is relative to the top level of the tree named
           by <dataref>.

                       'ls' SP <dataref> SP <path> LF

       See filemodify above for a detailed description of <path>.

       Output uses the same format as git ls-tree <tree> -- <path>:

           <mode> SP ('blob' | 'tree' | 'commit') SP <dataref> HT <path> LF

       The <dataref> represents the blob, tree, or commit object at <path> and
       can be used in later get-mark, cat-blob, filemodify, or ls commands.

       If there is no file or subtree at that path, git fast-import will instead
       report

           missing SP <path> LF

       See "Responses To Commands" below for details about how to read this
       output safely.

   feature
       Require that fast-import supports the specified feature, or abort if it
       does not.

                   'feature' SP <feature> ('=' <argument>)? LF

       The <feature> part of the command may be any one of the following:

       date-format, export-marks, relative-marks, no-relative-marks, force
           Act as though the corresponding command-line option with a leading --
           was passed on the command line (see OPTIONS, above).

       import-marks, import-marks-if-exists
           Like --import-marks except in two respects: first, only one "feature
           import-marks" or "feature import-marks-if-exists" command is allowed
           per stream; second, an --import-marks= or --import-marks-if-exists
           command-line option overrides any of these "feature" commands in the
           stream; third, "feature import-marks-if-exists" like a corresponding
           command-line option silently skips a nonexistent file.

       get-mark, cat-blob, ls
           Require that the backend support the get-mark, cat-blob, or ls
           command respectively. Versions of fast-import not supporting the
           specified command will exit with a message indicating so. This lets
           the import error out early with a clear message, rather than wasting
           time on the early part of an import before the unsupported command is
           detected.

       notes
           Require that the backend support the notemodify (N) subcommand to the
           commit command. Versions of fast-import not supporting notes will
           exit with a message indicating so.

       done
           Error out if the stream ends without a done command. Without this
           feature, errors causing the frontend to end abruptly at a convenient
           point in the stream can go undetected. This may occur, for example,
           if an import front end dies in mid-operation without emitting SIGTERM
           or SIGKILL at its subordinate git fast-import instance.

   option
       Processes the specified option so that git fast-import behaves in a way
       that suits the frontend's needs. Note that options specified by the
       frontend are overridden by any options the user may specify to git
       fast-import itself.

               'option' SP <option> LF

       The <option> part of the command may contain any of the options listed in
       the OPTIONS section that do not change import semantics, without the
       leading -- and is treated in the same way.

       Option commands must be the first commands on the input (not counting
       feature commands), to give an option command after any non-option command
       is an error.

       The following command-line options change import semantics and may
       therefore not be passed as option:

       o   date-format

       o   import-marks

       o   export-marks

       o   cat-blob-fd

       o   force

   done
       If the done feature is not in use, treated as if EOF was read. This can
       be used to tell fast-import to finish early.

       If the --done command-line option or feature done command is in use, the
       done command is mandatory and marks the end of the stream.


RESPONSES TO COMMANDS

       New objects written by fast-import are not available immediately. Most
       fast-import commands have no visible effect until the next checkpoint (or
       completion). The frontend can send commands to fill fast-import's input
       pipe without worrying about how quickly they will take effect, which
       improves performance by simplifying scheduling.

       For some frontends, though, it is useful to be able to read back data
       from the current repository as it is being updated (for example when the
       source material describes objects in terms of patches to be applied to
       previously imported objects). This can be accomplished by connecting the
       frontend and fast-import via bidirectional pipes:

           mkfifo fast-import-output
           frontend <fast-import-output |
           git fast-import >fast-import-output

       A frontend set up this way can use progress, get-mark, ls, and cat-blob
       commands to read information from the import in progress.

       To avoid deadlock, such frontends must completely consume any pending
       output from progress, ls, get-mark, and cat-blob before performing writes
       to fast-import that might block.


CRASH REPORTS

       If fast-import is supplied invalid input it will terminate with a
       non-zero exit status and create a crash report in the top level of the
       Git repository it was importing into. Crash reports contain a snapshot of
       the internal fast-import state as well as the most recent commands that
       lead up to the crash.

       All recent commands (including stream comments, file changes and progress
       commands) are shown in the command history within the crash report, but
       raw file data and commit messages are excluded from the crash report.
       This exclusion saves space within the report file and reduces the amount
       of buffering that fast-import must perform during execution.

       After writing a crash report fast-import will close the current packfile
       and export the marks table. This allows the frontend developer to inspect
       the repository state and resume the import from the point where it
       crashed. The modified branches and tags are not updated during a crash,
       as the import did not complete successfully. Branch and tag information
       can be found in the crash report and must be applied manually if the
       update is needed.

       An example crash:

           $ cat >in <<END_OF_INPUT
           # my very first test commit
           commit refs/heads/master
           committer Shawn O. Pearce <spearce> 19283 -0400
           # who is that guy anyway?
           data <<EOF
           this is my commit
           EOF
           M 644 inline .gitignore
           data <<EOF
           .gitignore
           EOF
           M 777 inline bob
           END_OF_INPUT

           $ git fast-import <in
           fatal: Corrupt mode: M 777 inline bob
           fast-import: dumping crash report to .git/fast_import_crash_8434

           $ cat .git/fast_import_crash_8434
           fast-import crash report:
               fast-import process: 8434
               parent process     : 1391
               at Sat Sep 1 00:58:12 2007

           fatal: Corrupt mode: M 777 inline bob

           Most Recent Commands Before Crash
           ---------------------------------
             # my very first test commit
             commit refs/heads/master
             committer Shawn O. Pearce <spearce> 19283 -0400
             # who is that guy anyway?
             data <<EOF
             M 644 inline .gitignore
             data <<EOF
           * M 777 inline bob

           Active Branch LRU
           -----------------
               active_branches = 1 cur, 5 max

           pos  clock name
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            1)      0 refs/heads/master

           Inactive Branches
           -----------------
           refs/heads/master:
             status      : active loaded dirty
             tip commit  : 0000000000000000000000000000000000000000
             old tree    : 0000000000000000000000000000000000000000
             cur tree    : 0000000000000000000000000000000000000000
             commit clock: 0
             last pack   :

           -------------------
           END OF CRASH REPORT


TIPS AND TRICKS

       The following tips and tricks have been collected from various users of
       fast-import, and are offered here as suggestions.

   Use One Mark Per Commit
       When doing a repository conversion, use a unique mark per commit (mark
       :<n>) and supply the --export-marks option on the command line.
       fast-import will dump a file which lists every mark and the Git object
       SHA-1 that corresponds to it. If the frontend can tie the marks back to
       the source repository, it is easy to verify the accuracy and completeness
       of the import by comparing each Git commit to the corresponding source
       revision.

       Coming from a system such as Perforce or Subversion this should be quite
       simple, as the fast-import mark can also be the Perforce changeset number
       or the Subversion revision number.

   Freely Skip Around Branches
       Don't bother trying to optimize the frontend to stick to one branch at a
       time during an import. Although doing so might be slightly faster for
       fast-import, it tends to increase the complexity of the frontend code
       considerably.

       The branch LRU builtin to fast-import tends to behave very well, and the
       cost of activating an inactive branch is so low that bouncing around
       between branches has virtually no impact on import performance.

   Handling Renames
       When importing a renamed file or directory, simply delete the old name(s)
       and modify the new name(s) during the corresponding commit. Git performs
       rename detection after-the-fact, rather than explicitly during a commit.

   Use Tag Fixup Branches
       Some other SCM systems let the user create a tag from multiple files
       which are not from the same commit/changeset. Or to create tags which are
       a subset of the files available in the repository.

       Importing these tags as-is in Git is impossible without making at least
       one commit which "fixes up" the files to match the content of the tag.
       Use fast-import's reset command to reset a dummy branch outside of your
       normal branch space to the base commit for the tag, then commit one or
       more file fixup commits, and finally tag the dummy branch.

       For example since all normal branches are stored under refs/heads/ name
       the tag fixup branch TAG_FIXUP. This way it is impossible for the fixup
       branch used by the importer to have namespace conflicts with real
       branches imported from the source (the name TAG_FIXUP is not
       refs/heads/TAG_FIXUP).

       When committing fixups, consider using merge to connect the commit(s)
       which are supplying file revisions to the fixup branch. Doing so will
       allow tools such as git blame to track through the real commit history
       and properly annotate the source files.

       After fast-import terminates the frontend will need to do rm
       .git/TAG_FIXUP to remove the dummy branch.

   Import Now, Repack Later
       As soon as fast-import completes the Git repository is completely valid
       and ready for use. Typically this takes only a very short time, even for
       considerably large projects (100,000+ commits).

       However repacking the repository is necessary to improve data locality
       and access performance. It can also take hours on extremely large
       projects (especially if -f and a large --window parameter is used). Since
       repacking is safe to run alongside readers and writers, run the repack in
       the background and let it finish when it finishes. There is no reason to
       wait to explore your new Git project!

       If you choose to wait for the repack, don't try to run benchmarks or
       performance tests until repacking is completed. fast-import outputs
       suboptimal packfiles that are simply never seen in real use situations.

   Repacking Historical Data
       If you are repacking very old imported data (e.g. older than the last
       year), consider expending some extra CPU time and supplying --window=50
       (or higher) when you run git repack. This will take longer, but will also
       produce a smaller packfile. You only need to expend the effort once, and
       everyone using your project will benefit from the smaller repository.

   Include Some Progress Messages
       Every once in a while have your frontend emit a progress message to
       fast-import. The contents of the messages are entirely free-form, so one
       suggestion would be to output the current month and year each time the
       current commit date moves into the next month. Your users will feel
       better knowing how much of the data stream has been processed.


PACKFILE OPTIMIZATION

       When packing a blob fast-import always attempts to deltify against the
       last blob written. Unless specifically arranged for by the frontend, this
       will probably not be a prior version of the same file, so the generated
       delta will not be the smallest possible. The resulting packfile will be
       compressed, but will not be optimal.

       Frontends which have efficient access to all revisions of a single file
       (for example reading an RCS/CVS ,v file) can choose to supply all
       revisions of that file as a sequence of consecutive blob commands. This
       allows fast-import to deltify the different file revisions against each
       other, saving space in the final packfile. Marks can be used to later
       identify individual file revisions during a sequence of commit commands.

       The packfile(s) created by fast-import do not encourage good disk access
       patterns. This is caused by fast-import writing the data in the order it
       is received on standard input, while Git typically organizes data within
       packfiles to make the most recent (current tip) data appear before
       historical data. Git also clusters commits together, speeding up revision
       traversal through better cache locality.

       For this reason it is strongly recommended that users repack the
       repository with git repack -a -d after fast-import completes, allowing
       Git to reorganize the packfiles for faster data access. If blob deltas
       are suboptimal (see above) then also adding the -f option to force
       recomputation of all deltas can significantly reduce the final packfile
       size (30-50% smaller can be quite typical).

       Instead of running git repack you can also run git gc --aggressive, which
       will also optimize other things after an import (e.g. pack loose refs).
       As noted in the "AGGRESSIVE" section in git-gc(1) the --aggressive option
       will find new deltas with the -f option to git-repack(1). For the reasons
       elaborated on above using --aggressive after a fast-import is one of the
       few cases where it's known to be worthwhile.


MEMORY UTILIZATION

       There are a number of factors which affect how much memory fast-import
       requires to perform an import. Like critical sections of core Git,
       fast-import uses its own memory allocators to amortize any overheads
       associated with malloc. In practice fast-import tends to amortize any
       malloc overheads to 0, due to its use of large block allocations.

   per object
       fast-import maintains an in-memory structure for every object written in
       this execution. On a 32 bit system the structure is 32 bytes, on a 64 bit
       system the structure is 40 bytes (due to the larger pointer sizes).
       Objects in the table are not deallocated until fast-import terminates.
       Importing 2 million objects on a 32 bit system will require approximately
       64 MiB of memory.

       The object table is actually a hashtable keyed on the object name (the
       unique SHA-1). This storage configuration allows fast-import to reuse an
       existing or already written object and avoid writing duplicates to the
       output packfile. Duplicate blobs are surprisingly common in an import,
       typically due to branch merges in the source.

   per mark
       Marks are stored in a sparse array, using 1 pointer (4 bytes or 8 bytes,
       depending on pointer size) per mark. Although the array is sparse,
       frontends are still strongly encouraged to use marks between 1 and n,
       where n is the total number of marks required for this import.

   per branch
       Branches are classified as active and inactive. The memory usage of the
       two classes is significantly different.

       Inactive branches are stored in a structure which uses 96 or 120 bytes
       (32 bit or 64 bit systems, respectively), plus the length of the branch
       name (typically under 200 bytes), per branch. fast-import will easily
       handle as many as 10,000 inactive branches in under 2 MiB of memory.

       Active branches have the same overhead as inactive branches, but also
       contain copies of every tree that has been recently modified on that
       branch. If subtree include has not been modified since the branch became
       active, its contents will not be loaded into memory, but if subtree src
       has been modified by a commit since the branch became active, then its
       contents will be loaded in memory.

       As active branches store metadata about the files contained on that
       branch, their in-memory storage size can grow to a considerable size (see
       below).

       fast-import automatically moves active branches to inactive status based
       on a simple least-recently-used algorithm. The LRU chain is updated on
       each commit command. The maximum number of active branches can be
       increased or decreased on the command line with --active-branches=.

   per active tree
       Trees (aka directories) use just 12 bytes of memory on top of the memory
       required for their entries (see "per active file" below). The cost of a
       tree is virtually 0, as its overhead amortizes out over the individual
       file entries.

   per active file entry
       Files (and pointers to subtrees) within active trees require 52 or 64
       bytes (32/64 bit platforms) per entry. To conserve space, file and tree
       names are pooled in a common string table, allowing the filename
       "Makefile" to use just 16 bytes (after including the string header
       overhead) no matter how many times it occurs within the project.

       The active branch LRU, when coupled with the filename string pool and
       lazy loading of subtrees, allows fast-import to efficiently import
       projects with 2,000+ branches and 45,114+ files in a very limited memory
       footprint (less than 2.7 MiB per active branch).


SIGNALS

       Sending SIGUSR1 to the git fast-import process ends the current packfile
       early, simulating a checkpoint command. The impatient operator can use
       this facility to peek at the objects and refs from an import in progress,
       at the cost of some added running time and worse compression.


CONFIGURATION

       Everything below this line in this section is selectively included from
       the git-config(1) documentation. The content is the same as what's found
       there:

       fastimport.unpackLimit
           If the number of objects imported by git-fast-import(1) is below this
           limit, then the objects will be unpacked into loose object files.
           However if the number of imported objects equals or exceeds this
           limit then the pack will be stored as a pack. Storing the pack from a
           fast-import can make the import operation complete faster, especially
           on slow filesystems. If not set, the value of transfer.unpackLimit is
           used instead.


SEE ALSO

       git-fast-export(1)


GIT

       Part of the git(1) suite



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