diff --git a/src/ShipItShellCommand.php b/src/ShipItShellCommand.php
new file mode 100644
index 00000000..229e6b03
--- /dev/null
+++ b/src/ShipItShellCommand.php
@@ -0,0 +1,146 @@
+<?hh
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+namespace Facebook\ShipIt;
+
+class ShipItShellCommand {
+  private ImmVector<string> $command;
+
+  private Map<string, string> $environmentVariables = Map {};
+  private bool $throwForNonZeroExit = true;
+  private ?string $stdin = null;
+  private bool $outputToScreen = false;
+
+  public function __construct(
+    private string $path,
+    ...$command
+  ) {
+    $this->command = new ImmVector($command);
+  }
+
+  public function setStdIn(string $input): this {
+    $this->stdin = $input;
+    return $this;
+  }
+
+  public function setOutputToScreen(): this {
+    $this->outputToScreen = true;
+    return $this;
+  }
+
+  public function setEnvironmentVariables(
+    ImmMap<string, string> $vars,
+  ): this {
+    $this->environmentVariables->setAll($vars);
+    return $this;
+  }
+
+  public function setNoExceptions(): this {
+    $this->throwForNonZeroExit = false;
+    return $this;
+  }
+
+  public function runSynchronously(): ShipItShellCommandResult {
+    $command = implode(' ', $this->command->map($str ==> escapeshellarg($str)));
+
+    $fds = array(
+      0 => array('pipe', 'r'),
+      1 => array('pipe', 'w'),
+      2 => array('pipe', 'w'),
+    );
+    $stdin = $this->stdin;
+    if ($stdin === null) {
+      unset($fds[0]);
+    }
+
+    $pipes = null;
+    $fp = proc_open(
+      $command,
+      $fds,
+      $pipes,
+      $this->path,
+      $this->environmentVariables->toArray(),
+    );
+    if (!$fp || !is_array($pipes)) {
+      throw new \Exception("Failed executing $command");
+    }
+    if ($stdin !== null) {
+      while (strlen($stdin)) {
+        $written = fwrite($pipes[0], $stdin);
+        $stdin = substr($stdin, $written);
+      }
+      fclose($pipes[0]);
+    }
+
+    $stdout_stream = $pipes[1];
+    $stderr_stream = $pipes[2];
+    stream_set_blocking($stdout_stream, false);
+    stream_set_blocking($stderr_stream, false);
+    $stdout = '';
+    $stderr = '';
+    while (true) {
+      $ready_streams = [$stdout_stream, $stderr_stream];
+      $null_byref = null;
+      $result = stream_select(
+        $ready_streams,
+        /* write streams = */ $null_byref,
+        /* exception streams = */ $null_byref,
+        /* timeout = */ null,
+      );
+      if ($result === false) {
+        break;
+      }
+      $all_empty = true;
+      foreach ($ready_streams as $stream) {
+        $out = fread($stream, 1024);
+        if (strlen($out) === 0) {
+          continue;
+        }
+        $all_empty = false;
+
+        if ($stream === $stdout_stream) {
+          $stdout .= $out;
+          $this->maybeFwrite(STDOUT, $out);
+          continue;
+        }
+        if ($stream === $stderr_stream) {
+          $stderr .= $out;
+          $this->maybeFwrite(STDERR, $out);
+          continue;
+        }
+
+        invariant_violation('Unhandled stream!');
+      }
+
+      if ($all_empty) {
+        break;
+      }
+    }
+    $exitcode = proc_close($fp);
+
+    $result = new ShipItShellCommandResult(
+      $exitcode,
+      $stdout,
+      $stderr,
+    );
+
+    if ($exitcode !== 0 && $this->throwForNonZeroExit) {
+      throw new ShipItShellCommandException($command, $result);
+    }
+
+    return $result;
+  }
+
+  private function maybeFwrite(resource $stream, string $out): void {
+    if (!$this->outputToScreen) {
+      return;
+    }
+    fwrite($stream, $out);
+  }
+}
diff --git a/src/ShipItShellCommandException.php b/src/ShipItShellCommandException.php
new file mode 100644
index 00000000..a745f344
--- /dev/null
+++ b/src/ShipItShellCommandException.php
@@ -0,0 +1,37 @@
+<?hh // strict
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+namespace Facebook\ShipIt;
+
+class ShipItShellCommandException extends \Exception {
+  public function __construct(
+    private string $command,
+    private ShipItShellCommandResult $result,
+  ) {
+    $exitCode = $result->getExitCode();
+    $error = $result->getStdErr();
+    parent::__construct("$command returned exit code $exitCode: $error");
+  }
+
+  public function getError(): string {
+    return $this->result->getStdErr();
+  }
+
+  public function getExitCode(): int {
+    return $this->result->getExitCode();
+  }
+
+  public function getOutput(): string {
+    return $this->result->getStdOut();
+  }
+
+  public function getResult(): ShipItShellCommandResult {
+    return $this->result;
+  }
+}
diff --git a/src/ShipItShellCommandResult.php b/src/ShipItShellCommandResult.php
new file mode 100644
index 00000000..ca290ae6
--- /dev/null
+++ b/src/ShipItShellCommandResult.php
@@ -0,0 +1,31 @@
+<?hh // strict
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+namespace Facebook\ShipIt;
+
+final class ShipItShellCommandResult {
+  public function __construct(
+    private int $exitCode,
+    private string $stdout,
+    private string $stderr,
+  ) {
+  }
+
+  public function getExitCode(): int {
+    return $this->exitCode;
+  }
+
+  public function getStdOut(): string {
+    return $this->stdout;
+  }
+
+  public function getStdErr(): string {
+    return $this->stderr;
+  }
+}
diff --git a/src/ShipItUtil.php b/src/ShipItUtil.php
index a88c3819..0f63888a 100644
--- a/src/ShipItUtil.php
+++ b/src/ShipItUtil.php
@@ -12,29 +12,6 @@
 type ShipItAffectedFile = string;
 type ShipItDiffAsString = string;
 
-class ShipItShellCommandException extends \Exception {
-  public function __construct(
-    private string $command,
-    private int $exitCode,
-    private string $output,
-    private string $error,
-  ) {
-    parent::__construct("$command returned exit code $exitCode: $error");
-  }
-
-  public function getError(): string {
-    return $this->error;
-  }
-
-  public function getExitCode(): int {
-    return $this->exitCode;
-  }
-
-  public function getOutput(): string {
-    return $this->output;
-  }
-}
-
 abstract class ShipItUtil {
   const SHORT_REV_LENGTH = 7;
   // flags for shellExec, no flag equal to 1
@@ -164,98 +141,40 @@ public static function isFileRemoval(string $body): bool {
     return (bool) preg_match('@^deleted file@m', $body);
   }
 
-  // readStreams reads from multiple streams in "parallel"
-  // (by using stream_select) which ensures that
-  // reading process won't block waiting for data in one stream when it
-  // appears in other
-  private static function readStreams(
-    array<resource> $streams,
-  ): array<string> {
-    $outs = array_fill(0, count($streams), '');
-    $reverse_map = array();
-
-    for ($i = 0; $i < count($streams); ++$i) {
-      stream_set_blocking($streams[$i], 0);
-      $reverse_map[$streams[$i]] = $i;
-    }
-    $stop = false;
-    while (!$stop) {
-      $null = null;
-      $ready_streams = $streams;
-      if (!stream_select($ready_streams, $null, $null, null)) {
-        $stop = true;
-      } else {
-        $all_empty = true;
-        foreach ($ready_streams as $stream) {
-          $out = fread($stream, 1024);
-          if ($out !== false && strlen($out) !== 0) {
-            $all_empty = false;
-            $outs[$reverse_map[$stream]] .= $out;
-          }
-        }
-        $stop = $all_empty;
-      }
-    }
-    return $outs;
-  }
-
   public static function shellExec(
     string $path,
     ?string $stdin,
     int $flags,
     ...$args
   ): string {
-    $fds = array(
-      0 => array('pipe', 'r'),
-      1 => array('pipe', 'w'),
-      2 => array('pipe', 'w'),
-    );
-    if ($stdin === null) {
-      unset($fds[0]);
-    }
+    $command = new ShipItShellCommand($path, ...$args);
 
-    $argn = null;
-    foreach ($args as &$argn) {
-      $argn = escapeshellarg($argn);
-    }
-    unset($argn);
-
-    $cmd = implode(' ', $args);
     if ($flags & self::VERBOSE_SHELL) {
+      $cmd = implode(' ', $args);
       fwrite(STDERR, "\$ $cmd\n");
     }
-    $pipes = null;
-    $fp = proc_open($cmd, $fds, $pipes, $path);
-    if (!$fp || !is_array($pipes)) {
-      throw new \Exception("Failed executing $cmd");
-    }
+
+
     if ($stdin !== null) {
       if ($flags & self::VERBOSE_SHELL_INPUT) {
         fwrite(STDERR, "--STDIN--\n$stdin\n");
       }
-      while (strlen($stdin)) {
-        $written = fwrite($pipes[0], $stdin);
-        $stdin = substr($stdin, $written);
-      }
-      fclose($pipes[0]);
+      $command->setStdIn($stdin);
     }
-    list($output, $error) = self::readStreams(array($pipes[1], $pipes[2]));
+
     if ($flags & self::VERBOSE_SHELL_OUTPUT) {
-      if ($error) {
-        fwrite(STDERR, "--STDERR--\n$error\n");
-      }
-      if ($output) {
-        fwrite(STDERR, "--STDOUT--\n$output\n");
-      }
+      $command->setOutputToScreen();
     }
-    $exitcode = proc_close($fp);
 
-    if ($exitcode && !($flags & self::NO_THROW)) {
-      throw new ShipItShellCommandException($cmd, $exitcode, $output, $error);
+    if ($flags && self::NO_THROW) {
+      $command->setNoExceptions();
     }
 
+    $result = $command->runSynchronously();
+
+    $output = $result->getStdOut();
     if ($flags & self::RETURN_STDERR) {
-      return $output."\n".$error;
+      $output .= "\n".$result->getStdErr();
     }
     return $output;
   }
diff --git a/tests/ShipItShellCommandTest.php b/tests/ShipItShellCommandTest.php
new file mode 100644
index 00000000..a7fdfe03
--- /dev/null
+++ b/tests/ShipItShellCommandTest.php
@@ -0,0 +1,86 @@
+<?hh // strict
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+namespace Facebook\ShipIt;
+
+final class ShipItShellCommandTest extends BaseTest {
+  public function testExitCodeZero(): void {
+    $result = (new ShipItShellCommand('/', 'true'))->runSynchronously();
+    $this->assertSame(0, $result->getExitCode());
+  }
+
+  public function testExitOneException(): void {
+    try {
+      (new ShipItShellCommand('/', 'false'))->runSynchronously();
+      $this->markTestFailed('Expected exception');
+    } catch (ShipItShellCommandException $e) {
+      $this->assertSame(1, $e->getExitCode());
+    }
+  }
+
+  public function testExitOneWithoutException(): void {
+    $result = (new ShipItShellCommand('/', 'false'))
+      ->setNoExceptions()
+      ->runSynchronously();
+    $this->assertSame(1, $result->getExitCode());
+  }
+
+  public function testStdIn(): void {
+    $result = (new ShipItShellCommand('/', 'cat'))
+      ->setStdIn('Hello, world.')
+      ->runSynchronously();
+    $this->assertSame('Hello, world.', $result->getStdOut());
+    $this->assertSame('', $result->getStdErr());
+  }
+
+  public function testEnvironmentVariables(): void {
+    $herp = bin2hex(random_bytes(16));
+    $result = (new ShipItShellCommand('/', 'env'))
+      ->setEnvironmentVariables(ImmMap { 'HERP' => $herp })
+      ->runSynchronously();
+    $this->assertContains(
+      'HERP='.$herp,
+      $result->getStdOut(),
+    );
+  }
+
+  public function testWorkingDirectory(): void {
+    $this->assertSame(
+      '/',
+      (new ShipItShellCommand('/', 'pwd'))
+        ->runSynchronously()
+        ->getStdOut()
+        |> trim($$),
+    );
+
+    $tmp = sys_get_temp_dir();
+    $this->assertSame(
+      $tmp,
+      (new ShipItShellCommand($tmp, 'pwd'))
+        ->runSynchronously()
+        ->getStdOut()
+        |> trim($$),
+    );
+  }
+
+  public function testMultipleArguments(): void {
+    $output = (new ShipItShellCommand('/', 'echo', '-n', 'foo', 'bar'))
+      ->runSynchronously()
+      ->getStdOut();
+    $this->assertSame('foo bar', $output);
+  }
+
+  public function testEscaping(): void {
+    $output = (new ShipItShellCommand('/', 'echo', 'foo', '$FOO'))
+      ->setEnvironmentVariables(ImmMap { 'FOO' => 'variable value' })
+      ->runSynchronously()
+      ->getStdOut();
+    $this->assertSame("foo \$FOO\n", $output);
+  }
+}