forkbridge

forkbridge is a small, well-tested Clojure library for spawning and interacting with subprocesses.

It provides a simple interface over Java's ProcessBuilder that lets you:

• Start and monitor long-lived processes
• Read and write lines from standard input/output in a safe, predictable way
• Gracefully or forcefully terminate subprocesses
• Wait for exit and capture exit codes

The API is minimal, transparent, and structured as a functional map with closures.

Installation

Check the appropriate instructions on Clojars:

https://clojars.org/org.clojars.martinjungblut/forkbridge

Example

(require '[forkbridge.core :refer [start-process]])

(def p (start-process ["clojure"]))

((:write-line! p) "(+ 1 2)")
(println ((:read-line-stdout! p))) ; => "user=> 3"

((:write-line! p) "(System/exit 0)")
((:wait! p))
(println ((:exit-value p))) ; => 0

API

Each call to start-process returns a map with the following keys:

Key	Description
:alive?	Returns true if the process is still running
:exit-value	Returns the exit code (or nil if the process hasn't exited yet)
:write-line!	Writes a line to the process's stdin (with a newline); returns true if successful, nil if the process is dead
:read-line-stdout!	Blocks until a full line is available from stdout; returns the line, or nil if the process is dead
:read-line-stderr!	Blocks until a full line is available from stderr; returns the line, or nil if the process is dead
:sigterm!	Sends SIGTERM to request graceful termination (non-blocking)
:sigkill!	Sends SIGKILL to forcibly terminate the process (non-blocking)
:wait!	Blocks until the process exits

Each of these is a function or thunk — to use them, call them like so:

((:write-line! p) "(+ 2 2)")
((:read-line-stdout! p)) ; => "user=> 4"

Use cases

• Embedding REPLs and long-running interpreters
• Orchestrating tools like Ansible or Bash scripts
• Interactive automation with line-by-line output control
• Safe process management in long-running systems

Testing

The test suite includes:

• Lifecycle validation (:alive?, :exit-value)
• Interactive I/O with a Clojure REPL subprocess
• Signal termination and proper exit code capture
• Verification of blocking operations (reading from stdout/stderr)

See forkbridge.core-test for working examples.

Philosophy

This library favours:

• Minimal state
• UNIX-style semantics
• Composability and testability

Comparison with babashka.process

While babashka.process is a powerful and flexible library for managing subprocesses, forkbridge offers a different tradeoff, with a focus on minimalism.

In the future, we may add some more features to forkbridge. We're still coming up with new ideas, but for now this is a usable base that just gets out of the way and provides some safety cushioning around interacting with subprocesses.

Strengths of forkbridge

• UNIX-style semantics: Explicit naming like :sigterm!, :sigkill!, :read-line-stdout!, etc. matches shell behavior clearly and transparently.
• Controlled and explicit I/O: Line-based readers and writers with newline-handling by default.

When to use babashka.process instead

• You want tight integration with the Babashka runtime or use it in scripting contexts.
• You need piping or redirection across multiple subprocesses (e.g., ls | grep foo).
• You need automatic stream handling (e.g., :inherit, :string, or background execution).
• You prefer a higher-level API with more built-in options for capturing and manipulating process output.

Licence

MIT Licence. See LICENCE for details.