diff --git a/rash.rkt b/rash.rkt
index bee2fcf..65f6d3f 100644
--- a/rash.rkt
+++ b/rash.rkt
@@ -1,16 +1,31 @@
 #lang racket/base
 
-(require readline/readline)
 (require racket/string)
 
-(define (do command . args)
-  (let ([cmd (find-executable-path command)])
+(provide run)
+
+(define (run command . args)
+  (let ([cmd (find-executable-path command)]
+        [output-port (file-port? (current-output-port))]
+        [input-port (file-port? (current-input-port))]
+        [error-port (file-port? (current-error-port))])
     (if cmd
         (let-values ([(subproc in out err)
-                      (subprocess (current-output-port)
-                                  (current-input-port)
-                                  (current-error-port)
+                      (subprocess output-port
+                                  input-port
+                                  error-port
                                   cmd
                                   (string-join args " "))])
-          (subprocess-wait subproc))
-        (raise (exn:fail:filesystem command)))))
+          (subprocess-wait subproc)
+          (when (input-port? in)
+            (close-input-port in))
+          (when (output-port? out)
+            (close-output-port out))
+          (when (output-port? err)
+            (close-output-port err)))
+        (raise (string-append command ": command not found")))))
+
+(define (file-port? port)
+  (if (file-stream-port? port)
+      port
+      #f))