git-remote-ext

git remote-ext [--stdin] [--stdout] [--stderr] helper url

--stdin
    Read transport requests from stdin (testing mode, skips spawning helper)

--stdout
    Write responses to stdout (testing mode)

--stderr
    Send diagnostics to stderr (testing mode)

helper
    Executable name or path (searched in $PATH or absolute)

url
    Full remote URL passed to helper (e.g., exec:///path)

git-remote-ext is a low-level Git plumbing command used to execute arbitrary external programs as custom remote transport helpers. It enables Git to interact with remote repositories via non-native protocols by spawning an executable helper that communicates over stdin/stdout/stderr. Git automatically invokes git-remote-ext when a remote URL uses the exec:// scheme. For example:
git remote add origin exec:///usr/local/bin/my-helper
This results in Git running git-remote-ext my-helper exec:///usr/local/bin/my-helper during operations like fetch or push. The helper (basename or path) must implement Git's remote helper protocol (see git-remote-helpers(7)). It handles commands such as capabilities, list for refs, import/export for objects, and connect. Helpers can support push, fetch, or both, and declare capabilities like connect or push. Use cases include integrating with cloud APIs (e.g., git-remote-bzr, git-remote-hg), proprietary systems, or shell wrappers for APIs. For helpers in $PATH, use exec::helpername; for full paths, exec:///full/path (three slashes). Options like --stdin aid testing without full Git integration.

Plumbing command; not for direct use. Helper must strictly follow protocol or Git operations fail. Absolute paths use exec:/// (three slashes); relative/searchable use exec::. Security risk if helper untrusted.

git remote add foo exec::myhelper arg1
or
git remote add bar exec:///opt/bin/custom-helper
Then git fetch foo invokes helper via git-remote-ext.

Must print capabilities first (e.g., fetch push), handle list for refs. Full spec in git-remote-helpers(7).

Part of Git's remote helpers framework since v1.6.6 (2008); exec:// support added v1.7.7 (2010) for arbitrary executables beyond prefixed git-remote-*. Evolved for better custom transport integration.

git-remote(1), git-remote-helpers(7), git-fetch(1), git-push(1)