Phing condition for testing if an executable is available on the system.

gistfile1.php

<?php
/**
 * Phing task to test if a given external program is avilable on the system
 *
 * Internally this uses "which" on Linux / OSX and "where" on Windows to locate the executable
 * 
 * Usage:
 * Put the file in a subfolder called "tasks", and use as follows:
 * 
 * <typedef name="exists" classname="tasks.ExistsCondition"/> 
 * <targetname="test">
 * <if>
 * 	<exists command="uglifyjs">
 * 	<then>
 * 	...
 * </if>
 * </target>
 * 
 * @author Doug Fitzmaurice
 * @link https://gist.github.com/dig412
 */
class ExistsCondition implements Condition {
	
	/**
	 * The command we are testing the existance of
	 * @var string
	 */
	private $command      = null;

	/**
	 * The system command for locating executables (Which or Where)
	 * @var string
	 */
	private $whichCommand = null;

	/**
	 * Setter for the "command" proerty
	 * @param string $command Name of the command that will be located (e.g. "uglifyjs")
	 */
	public function setCommand($command) {
		$this->command = $command;
	}

	public function evaluate() {

		$this->setWhichCommand();

		exec("{$this->whichCommand} {$this->command} 2>&1", $output, $returnCode);

		if($returnCode == 0) {
			return true;
		}
		else {
			return false;
		}
	}

	/**
	 * Sets the "which" implementation for the current OS
	 */
	private function setWhichCommand() {

		$os = Phing::getProperty("host.os");

		switch($os) {
			case "WINNT":
				$this->whichCommand = "where";
				break;

			case "Linux":
			case "Darwin":
				$this->whichCommand = "which";
				break;

			default:
				throw new BuildException("Not a known OS - $os");
		}
	}

}