This seems to work.

README.md

@@ -1,12 +1,20 @@
 # bashpipe
 
-A this point, only a small experiment using a long lived shell process
-to execute stuff faster than spawning a different process everytime
-with clojure.java.shell/sh.
+This small experiment maintains a long-lived bash process used to
+execute system commands. The objective is not having to spawn a
+process for every call like clojure.java.shell.
 
 ## Usage
 
-FIXME
+```
+(bashpipe.core/sh "ls" "-la")
+```
+
+## Issues
+
+Having a single bash process means that commands are executed sequentially and that if one command hangs, it will block all other commands.
+
+A named pipe is created in the mechanism of communication with the bash process. That named pipe is never removed.
 
 ## License
 

project.clj

@@ -1,6 +1,10 @@
 (defproject bashpipe "0.1.0-SNAPSHOT"
-  :description "FIXME: write description"
-  :url "http://example.com/FIXME"
+  :description "Library maintaining a long-lived bash shell in order
+  not to spawn a process everytime you shell out."
+  :url "http://github.com/jsab/bashpipe"
   :license {:name "Eclipse Public License"
             :url "http://www.eclipse.org/legal/epl-v10.html"}
-  :dependencies [[org.clojure/clojure "1.5.1"]])
+  :min-lein-version "2.0.0"
+  :dependencies [[org.clojure/clojure "1.5.1"]]
+  :global-vars {*warn-on-reflection* true
+                *assert* false})

src/bashpipe/core.clj

@@ -1,8 +1,10 @@
 (ns bashpipe.core
-  (:require [clojure.java.io :as io]))
+  (:require [clojure.java.io :as io]
+            [clojure.java.shell :as shell]))
 
 
-(defn run [^String cmd]
+(defn- run [cmd]
+  "Used to build the long lived bash process."
   (let [string-array ^"[Ljava.lang.String;" (into-array String cmd)
         builder (ProcessBuilder. string-array)
         process (.start builder)]
@@ -12,19 +14,44 @@
      :process process}))
 
 
-(def bash (run ["bash"]))
+(defonce bash (run ["bash"]))
+(defonce bash-lock (Object.))
+(defonce pipe-path (clojure.string/trim
+                    (:out (shell/sh "mktemp" "-u" "-t" "bashpipe"))))
 
+(shell/sh "mkfifo" pipe-path)
 
-(defn put! [command]
+
+(defn- send! [command]
   (let [stream ^java.io.OutputStream (:in bash)]
-    (io/copy (java.io.StringReader. (str command "\n"))
+    (io/copy (java.io.StringReader. (str command "; echo -n $? > " pipe-path "\n"))
              stream)
     (.flush stream)))
 
 
-(defn get! []
-  (let [stream ^java.io.InputStream (:out bash)
-        avail (.available stream)
+(defn- read-stream [^java.io.InputStream stream]
+  (let [avail (.available stream)
         bytes (byte-array avail)]
     (.read stream bytes)
     (String. bytes)))
+
+
+(defn- read-out []
+  (read-stream (:out bash)))
+
+
+(defn- read-err []
+  (read-stream (:err bash)))
+
+
+(defn sh [& args]
+  "Passes the given arguments to bash.
+
+Returns a map containing output of the command in :out and :err
+  and the exit code in :exit."
+  (locking bash-lock
+    (send! (apply str args))
+    (let [exit-code (Long/decode (slurp pipe-path))]
+      {:exit exit-code
+       :out (read-out)
+       :err (read-err)})))