Git Fast Import Commands: Alias, Checkpoint, Progress, Get-Mark, Cat-Blob, and Ls

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

The git-fast-import command provides additional options for managing the import process, including recording object aliases, forcing checkpoints, printing progress lines, retrieving SHA-1s, printing blobs, and printing object information, allowing frontends to interact with the Git repository and create a stream of commands for fast-import to process, with specific syntax and rules for each command to manage the import process and retrieve data from the repository.