--- /dev/null
+<?php
+
+/*
+ * This file is part of Psy Shell.
+ *
+ * (c) 2012-2017 Justin Hileman
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Psy\Output;
+
+use Symfony\Component\Console\Output\StreamOutput;
+
+/**
+ * ProcOutputPager class.
+ *
+ * A ProcOutputPager instance wraps a regular StreamOutput's stream. Rather
+ * than writing directly to the stream, it shells out to a pager process and
+ * gives that process the stream as stdout. This means regular *nix commands
+ * like `less` and `more` can be used to page large amounts of output.
+ */
+class ProcOutputPager extends StreamOutput implements OutputPager
+{
+ private $proc;
+ private $pipe;
+ private $stream;
+ private $cmd;
+
+ /**
+ * Constructor.
+ *
+ * @param StreamOutput $output
+ * @param string $cmd Pager process command (default: 'less -R -S -F -X')
+ */
+ public function __construct(StreamOutput $output, $cmd = 'less -R -S -F -X')
+ {
+ $this->stream = $output->getStream();
+ $this->cmd = $cmd;
+ }
+
+ /**
+ * Writes a message to the output.
+ *
+ * @param string $message A message to write to the output
+ * @param bool $newline Whether to add a newline or not
+ *
+ * @throws \RuntimeException When unable to write output (should never happen)
+ */
+ public function doWrite($message, $newline)
+ {
+ $pipe = $this->getPipe();
+ if (false === @fwrite($pipe, $message . ($newline ? PHP_EOL : ''))) {
+ // @codeCoverageIgnoreStart
+ // should never happen
+ throw new \RuntimeException('Unable to write output.');
+ // @codeCoverageIgnoreEnd
+ }
+
+ fflush($pipe);
+ }
+
+ /**
+ * Close the current pager process.
+ */
+ public function close()
+ {
+ if (isset($this->pipe)) {
+ fclose($this->pipe);
+ }
+
+ if (isset($this->proc)) {
+ $exit = proc_close($this->proc);
+ if ($exit !== 0) {
+ throw new \RuntimeException('Error closing output stream');
+ }
+ }
+
+ unset($this->pipe, $this->proc);
+ }
+
+ /**
+ * Get a pipe for paging output.
+ *
+ * If no active pager process exists, fork one and return its input pipe.
+ */
+ private function getPipe()
+ {
+ if (!isset($this->pipe) || !isset($this->proc)) {
+ $desc = array(array('pipe', 'r'), $this->stream, fopen('php://stderr', 'w'));
+ $this->proc = proc_open($this->cmd, $desc, $pipes);
+
+ if (!is_resource($this->proc)) {
+ throw new \RuntimeException('Error opening output stream');
+ }
+
+ $this->pipe = $pipes[0];
+ }
+
+ return $this->pipe;
+ }
+}