git-remote-ext

git remote add name ext::command [arguments]
git clone ext::command [arguments] [directory]

ext::
    The literal prefix that signals Git to use the git-remote-ext helper for the subsequent part of the URL.

command
    The path to an executable program or script that implements the Git remote helper protocol. This can be a command found in the system's PATH (e.g., my-custom-git-helper) or an absolute path (e.g., /usr/local/bin/my-helper). If an absolute path is used, it often requires an additional slash after ext::, e.g., ext:///path/to/command.

arguments
    Optional, space-separated arguments to be passed directly to the command. These arguments are URL-decoded by git-remote-ext before being passed to the external helper.

git-remote-ext is a specialized Git remote helper that enables Git to interact with repositories via arbitrary external programs. Instead of relying on built-in protocols like HTTP or SSH, this helper acts as a bridge, delegating all remote operations (like fetching, pushing, or listing references) to an executable specified in the remote URL. When a Git remote URL is prefixed with ext::, Git invokes git-remote-ext, which then executes the designated external command. This external command is expected to adhere to Git's remote helper protocol, communicating with Git via standard input and output.

This mechanism provides unparalleled flexibility, allowing Git to integrate with custom storage solutions, proprietary version control systems, or non-standard network protocols by simply writing a wrapper script or binary that conforms to the protocol. It is particularly useful for extending Git's reach into environments not natively supported, offering a powerful way to customize how Git interacts with various backends.

Security Risk: Using git-remote-ext with untrusted sources or specifying arbitrary commands can pose a significant security risk, as it executes external programs. Always ensure the specified command is trustworthy and secure.
Protocol Implementation: The external command must correctly implement the Git remote helper protocol (as detailed in git-remote-helpers(7)) to function properly. Incorrect implementation will lead to errors or unexpected behavior.
Performance: The performance of remote operations depends entirely on the efficiency and responsiveness of the external helper program and the underlying transport or system it interacts with.

The core functionality of git-remote-ext relies on the external program implementing a specific communication protocol. This protocol defines how Git sends commands (like capabilities, list, fetch, push) to the helper via standard input and how the helper responds via standard output. A thorough understanding of this protocol, as documented in git-remote-helpers(7), is essential for writing effective external helpers.

Unlike most Git commands, git-remote-ext is not invoked directly from the command line. Instead, it is implicitly used by Git when a remote URL starts with the ext:: prefix. This makes it a powerful background mechanism for custom remote integrations.

The concept of remote helpers is a foundational aspect of Git's extensibility model, designed to allow integration with various protocols and storage backends beyond its native capabilities. git-remote-ext specifically provides a generic mechanism to plug in *any* executable that conforms to the remote helper protocol. This flexibility allows users to integrate Git with highly customized systems, proprietary solutions, or niche network environments without requiring Git's core codebase to support them directly. It was introduced to maximize the adaptability and reach of Git's remote operations.

git(1), git-remote(1), git-clone(1), git-remote-helpers(7)