diff --git a/.DS_Store b/.DS_Store
new file mode 100644
index 0000000..eb856df
Binary files /dev/null and b/.DS_Store differ
diff --git a/result b/result
new file mode 120000
index 0000000..cbbdaa1
--- /dev/null
+++ b/result
@@ -0,0 +1 @@
+/nix/store/wllb7d3wx2wh2p4h8vj7y10p31f37jd8-runwhen-0.0.4
\ No newline at end of file
diff --git a/src/error.rs b/src/error.rs
index ee70488..88af249 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -12,6 +12,7 @@
 //  See the License for the specific language governing permissions and
 //  limitations under the License.
 use std::fmt;
+use std::io;
 
 use notify;
 
@@ -37,3 +38,9 @@ impl From<notify::Error> for CommandError {
         CommandError::new(format!("{}", e))
     }
 }
+
+impl From<io::Error> for CommandError {
+    fn from(e: io::Error) -> CommandError {
+        CommandError::new(format!("IO: {}", e))
+    }
+}
diff --git a/src/exec.rs b/src/exec.rs
index 6957c84..624f256 100644
--- a/src/exec.rs
+++ b/src/exec.rs
@@ -11,11 +11,10 @@
 //  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 //  See the License for the specific language governing permissions and
 //  limitations under the License.
+use std::process::{Child, Command, Stdio};
 use std::thread;
 use std::time::Duration;
 
-use std::process::{Command, Stdio};
-
 use error::CommandError;
 use traits::Process;
 
@@ -30,79 +29,147 @@ fn env_var_to_tuple(var: &str) -> (String, String) {
     ("".to_string(), "".to_string())
 }
 
-pub fn run_cmd(cmd: &str, env: &Option<Vec<&str>>) -> Result<i32, CommandError> {
-    let args = cmd
-        .split(' ')
-        .filter(|s| !s.is_empty())
-        .collect::<Vec<&str>>();
-    if args.len() < 1 {
-        return Err(CommandError::new("Empty command string passed in"));
-    }
-    let mut exec = Command::new(args[0]);
-    if args.len() > 1 {
-        exec.args(&args[1..]);
-    }
-    exec.stdout(Stdio::inherit());
-    exec.stderr(Stdio::inherit());
-    if let &Some(ref env_vars) = env {
-        for var in env_vars {
-            let tpl = env_var_to_tuple(var);
-            exec.env(tpl.0, tpl.1);
+pub struct CancelableProcess {
+    cmd: String,
+    env: Option<Vec<String>>,
+    exec: Option<Command>,
+    handle: Option<Child>,
+}
+
+impl CancelableProcess {
+    pub fn new(cmd: &str, env: Option<Vec<String>>) -> Self {
+        Self {
+            cmd: cmd.to_string(),
+            env,
+            exec: None,
+            handle: None,
         }
     }
-    return match exec.output() {
-        Ok(out) => match out.status.code() {
-            Some(val) => Ok(val),
-            None => Ok(0),
-        },
-        // TODO(jeremy): We should not swallow this error.
-        Err(_) => Err(CommandError::new("Error running command")),
-    };
-}
 
-fn is_cmd_success(cmd: &str, env: Option<Vec<&str>>) -> bool {
-    match run_cmd(cmd, &env) {
-        Ok(code) => code == 0,
-        _ => false,
+    fn create_command(cmd: &str, env: &Option<Vec<String>>) -> Result<Command, CommandError> {
+        let args = cmd
+            .split(' ')
+            .filter(|s| !s.is_empty())
+            .collect::<Vec<&str>>();
+        if args.len() < 1 {
+            return Err(CommandError::new("Empty command string passed in"));
+        }
+        let mut exec = Command::new(args[0]);
+        if args.len() > 1 {
+            exec.args(&args[1..]);
+        }
+        exec.stdout(Stdio::inherit());
+        exec.stderr(Stdio::inherit());
+        if let &Some(ref env_vars) = env {
+            for var in env_vars {
+                let tpl = env_var_to_tuple(var);
+                exec.env(tpl.0, tpl.1);
+            }
+        }
+        return Ok(exec);
+    }
+
+    pub fn block(&mut self) -> Result<i32, CommandError> {
+        if let Some(ref mut handle) = self.handle {
+            let code = handle.wait()?.code().unwrap_or(0);
+            self.exec = None;
+            self.handle = None;
+            Ok(code)
+        } else {
+            let mut exec = Self::create_command(&self.cmd, &self.env)?;
+            return match exec.output() {
+                Ok(out) => match out.status.code() {
+                    Some(val) => Ok(val),
+                    None => Ok(0),
+                },
+                // TODO(jeremy): We should not swallow this error.
+                Err(_) => Err(CommandError::new("Error running command")),
+            };
+        }
+    }
+
+    pub fn is_success(&mut self) -> bool {
+        match self.block() {
+            Ok(code) => code == 0,
+            _ => false,
+        }
+    }
+
+    pub fn check(&mut self) -> Result<Option<i32>, CommandError> {
+        Ok(match self.handle {
+            Some(ref mut h) => match h.try_wait()? {
+                Some(status) => Some(status.code().unwrap_or(0)),
+                None => Some(h.wait()?.code().unwrap_or(0)),
+            },
+            None => None,
+        })
+    }
+
+    pub fn spawn(&mut self) -> Result<(), CommandError> {
+        let mut exec = Self::create_command(&self.cmd, &self.env)?;
+        let handle = exec.spawn()?;
+        self.exec = Some(exec);
+        self.handle = Some(handle);
+        Ok(())
+    }
+
+    pub fn cancel(&mut self) -> Result<(), CommandError> {
+        if let Some(ref mut h) = self.handle {
+            h.kill()?;
+        }
+        self.exec = None;
+        self.handle = None;
+        Ok(())
+    }
+
+    pub fn reset(&mut self) -> Result<(), CommandError> {
+        self.cancel()?;
+        self.spawn()?;
+        Ok(())
     }
 }
 
-pub struct ExecProcess<'a> {
-    test_cmd: &'a str,
+// TODO(jwall): Make these CancelableProcess instead.
+pub struct ExecProcess {
+    test_cmd: CancelableProcess,
     negate: bool,
-    cmd: &'a str,
-    env: Option<Vec<&'a str>>,
+    cmd: CancelableProcess,
     poll: Duration,
 }
 
-impl<'a> ExecProcess<'a> {
+impl ExecProcess {
     pub fn new(
-        test_cmd: &'a str,
-        cmd: &'a str,
+        test_cmd: &str,
+        cmd: &str,
         negate: bool,
-        env: Option<Vec<&'a str>>,
+        env: Option<Vec<String>>,
         poll: Duration,
-    ) -> ExecProcess<'a> {
+    ) -> ExecProcess {
+        let test_cmd = CancelableProcess::new(test_cmd, None);
+        let cmd = CancelableProcess::new(cmd, env);
         ExecProcess {
-            test_cmd: test_cmd,
-            negate: negate,
-            cmd: cmd,
-            env: env,
-            poll: poll,
+            test_cmd,
+            negate,
+            cmd,
+            poll,
+        }
+    }
+
+    fn run_loop_step(&mut self) {
+        let test_result = self.test_cmd.is_success();
+        if (test_result && !self.negate) || (!test_result && self.negate) {
+            if let Err(err) = self.cmd.block() {
+                println!("{:?}", err)
+            }
         }
     }
 }
 
-impl<'a> Process for ExecProcess<'a> {
-    fn run(&self) -> Result<(), CommandError> {
+impl Process for ExecProcess {
+    fn run(&mut self) -> Result<(), CommandError> {
         loop {
             // TODO(jwall): Should we set the environment the same as the other command?
-            let test_result = is_cmd_success(self.test_cmd, None);
-            if (test_result && !self.negate) || (!test_result && self.negate) {
-                if let Err(err) = run_cmd(self.cmd, &self.env) {
-                    println!("{:?}", err)
-                }
-            }
+            self.run_loop_step();
             thread::sleep(self.poll);
         }
     }
diff --git a/src/file.rs b/src/file.rs
index 5adc38e..0f071e0 100644
--- a/src/file.rs
+++ b/src/file.rs
@@ -21,12 +21,12 @@ use notify::{watcher, RecursiveMode, Watcher};
 
 use error::CommandError;
 use events::WatchEventType;
-use exec::run_cmd;
+use exec::CancelableProcess;
 use traits::Process;
 
 pub struct FileProcess<'a> {
     cmd: &'a str,
-    env: Option<Vec<&'a str>>,
+    env: Option<Vec<String>>,
     files: Vec<&'a str>,
     method: WatchEventType,
     poll: Duration,
@@ -35,17 +35,17 @@ pub struct FileProcess<'a> {
 impl<'a> FileProcess<'a> {
     pub fn new(
         cmd: &'a str,
-        env: Option<Vec<&'a str>>,
+        env: Option<Vec<String>>,
         file: Vec<&'a str>,
         method: WatchEventType,
         poll: Duration,
     ) -> FileProcess<'a> {
         FileProcess {
-            cmd: cmd,
-            env: env,
+            cmd,
+            env,
+            method,
+            poll,
             files: file,
-            method: method,
-            poll: poll,
         }
     }
 }
@@ -53,7 +53,7 @@ impl<'a> FileProcess<'a> {
 fn spawn_runner_thread(
     lock: Arc<Mutex<bool>>,
     cmd: String,
-    env: Option<Vec<&str>>,
+    env: Option<Vec<String>>,
     poll: Duration,
 ) {
     let copied_env = env.and_then(|v| {
@@ -65,42 +65,46 @@ fn spawn_runner_thread(
         )
     });
     thread::spawn(move || {
-        let copied_env_refs: Option<Vec<&str>> = match copied_env {
-            Some(ref vec) => {
-                let mut refs: Vec<&str> = Vec::new();
-                for s in vec.iter() {
-                    refs.push(s);
-                }
-                Some(refs)
-            }
-            None => None,
-        };
+        let mut exec = CancelableProcess::new(&cmd, copied_env);
+        exec.spawn().expect("Failed to start command");
         loop {
             // Wait our requisit number of seconds
             thread::sleep(poll);
             // Default to not running the command.
-            match lock.lock() {
-                Ok(mut signal) => {
-                    if *signal {
-                        // set signal to false so we won't trigger on the
-                        // next loop iteration unless we recieved more events.
-                        *signal = false;
-                        // Run our command!
-                        println!("exec: {}", cmd);
-                        if let Err(err) = run_cmd(&cmd, &copied_env_refs) {
-                            println!("{:?}", err)
-                        }
-                    }
-                }
-                Err(err) => {
-                    println!("Unexpected error; {}", err);
-                    return;
-                }
+            if !run_loop_step(lock.clone(), &mut exec) {
+                exec.reset().expect("Failed to start command");
             }
         }
     });
 }
 
+fn run_loop_step(lock: Arc<Mutex<bool>>, exec: &mut CancelableProcess) -> bool {
+    match lock.lock() {
+        Ok(mut signal) => {
+            // We always want to check on our process each iteration of the loop.
+            if let Err(err) = exec.check() {
+                println!("{:?}", err);
+                return false;
+            }
+            if *signal {
+                // set signal to false so we won't trigger on the
+                // next loop iteration unless we recieved more events.
+                *signal = false;
+                // On a true signal we want to start or restart our process.
+                if let Err(err) = exec.reset() {
+                    println!("{:?}", err);
+                    return false;
+                }
+            }
+            return true;
+        }
+        Err(err) => {
+            println!("Unexpected error; {}", err);
+            return false;
+        }
+    }
+}
+
 fn wait_for_fs_events(
     lock: Arc<Mutex<bool>>,
     method: WatchEventType,
@@ -153,7 +157,7 @@ fn wait_for_fs_events(
 }
 
 impl<'a> Process for FileProcess<'a> {
-    fn run(&self) -> Result<(), CommandError> {
+    fn run(&mut self) -> Result<(), CommandError> {
         // TODO(jeremy): Is this sufficent or do we want to ignore
         // any events that come in while the command is running?
         let lock = Arc::new(Mutex::new(false));
diff --git a/src/main.rs b/src/main.rs
index 9f3b3f0..b96cf4c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -72,12 +72,11 @@ fn main() {
     if let Some(env_values) = app.values_of("env") {
         let mut env_vec = Vec::new();
         for v in env_values {
-            env_vec.push(v);
+            env_vec.push(v.to_string());
         }
         maybe_env = Some(env_vec);
     }
-    let mut process: Option<Box<dyn Process>> = None;
-    if let Some(matches) = app.subcommand_matches("watch") {
+    let mut proc: Box<dyn Process> = if let Some(matches) = app.subcommand_matches("watch") {
         let file = match matches.values_of("file") {
             Some(v) => v.collect(),
             // The default is our current directory
@@ -91,19 +90,16 @@ fn main() {
             .get_one::<humantime::Duration>("poll")
             .cloned()
             .unwrap_or(humantime::Duration::from_str("5s").unwrap());
-        process = Some(Box::new(FileProcess::new(
-            cmd, maybe_env, file, method, duration,
-        )));
+        Box::new(FileProcess::new(cmd, maybe_env, file, method, duration))
     } else if let Some(matches) = app.subcommand_matches("timer") {
+        // TODO(jwall): This should use cancelable commands.
         // Unwrap because this flag is required.
         let duration = matches
             .get_one::<humantime::Duration>("duration")
             .expect("duration flag is required")
             .clone();
         let max_repeat = matches.get_one::<u32>("repeat").cloned();
-        process = Some(Box::new(TimerProcess::new(
-            cmd, maybe_env, *duration, max_repeat,
-        )));
+        Box::new(TimerProcess::new(cmd, maybe_env, *duration, max_repeat))
     } else if let Some(matches) = app.subcommand_matches("success") {
         // unwrap because this is required.
         let ifcmd = matches.value_of("ifcmd").expect("ifcmd flag is required");
@@ -112,20 +108,15 @@ fn main() {
             .get_one::<humantime::Duration>("poll")
             .cloned()
             .unwrap_or(humantime::Duration::from_str("5s").unwrap());
-        Some(Box::new(ExecProcess::new(
-            ifcmd, cmd, negate, maybe_env, duration,
-        )));
-    }
-    match process {
-        Some(process) => match process.run() {
-            Ok(_) => return,
-            Err(err) => {
-                println!("{0}", err);
-                process::exit(1)
-            }
-        },
-        None => {
-            println!("You must specify a subcommand.");
+        Box::new(ExecProcess::new(ifcmd, cmd, negate, maybe_env, duration))
+    } else {
+        println!("You must specify a subcommand.");
+        process::exit(1)
+    };
+    match proc.run() {
+        Ok(_) => return,
+        Err(err) => {
+            println!("{0}", err);
             process::exit(1)
         }
     }
diff --git a/src/timer.rs b/src/timer.rs
index 8fcec69..0dd634e 100644
--- a/src/timer.rs
+++ b/src/timer.rs
@@ -14,41 +14,40 @@
 use std::thread;
 use std::time::Duration;
 
+use exec::CancelableProcess;
 use error::CommandError;
-use exec::run_cmd;
 use traits::Process;
 
-pub struct TimerProcess<'a> {
-    cmd: &'a str,
-    env: Option<Vec<&'a str>>,
+pub struct TimerProcess {
+    cmd: CancelableProcess,
     poll_duration: Duration,
     max_repeat: Option<u32>,
 }
 
-impl<'a> TimerProcess<'a> {
+impl TimerProcess {
     pub fn new(
-        cmd: &'a str,
-        env: Option<Vec<&'a str>>,
+        cmd: &str,
+        env: Option<Vec<String>>,
         poll_duration: Duration,
         max_repeat: Option<u32>,
-    ) -> TimerProcess<'a> {
+    ) -> TimerProcess {
+    let cmd = CancelableProcess::new(cmd, env);
         TimerProcess {
-            cmd: cmd,
-            env: env,
-            poll_duration: poll_duration,
-            max_repeat: max_repeat,
+            cmd,
+            poll_duration,
+            max_repeat,
         }
     }
 }
 
-impl<'a> Process for TimerProcess<'a> {
-    fn run(&self) -> Result<(), CommandError> {
+impl Process for TimerProcess {
+    fn run(&mut self) -> Result<(), CommandError> {
         let mut counter = 0;
         loop {
             if self.max_repeat.is_some() && counter >= self.max_repeat.unwrap() {
                 return Ok(());
             }
-            if let Err(err) = run_cmd(self.cmd, &self.env) {
+            if let Err(err) = self.cmd.block() {
                 println!("{:?}", err)
             }
             thread::sleep(self.poll_duration);
diff --git a/src/traits.rs b/src/traits.rs
index 842203b..bec6be7 100644
--- a/src/traits.rs
+++ b/src/traits.rs
@@ -14,5 +14,5 @@
 use error::CommandError;
 
 pub trait Process {
-    fn run(&self) -> Result<(), CommandError>;
+    fn run(&mut self) -> Result<(), CommandError>;
 }