diff --git a/src/_h5ai/server/php/inc/setup.php b/src/_h5ai/server/php/inc/setup.php
index 74ac2645..3d22abc8 100644
--- a/src/_h5ai/server/php/inc/setup.php
+++ b/src/_h5ai/server/php/inc/setup.php
@@ -84,8 +84,15 @@ function setup() {
 
 
 	// EXTERNAL COMMANDS
-	foreach (array("tar", "zip", "convert", "ffmpeg", "avconv", "du") as $cmd) {
-		$cmdv = HAS_WIN_OS ? array("which", $cmd) : array("command", "-v", $cmd);
-		define("HAS_CMD_" . strtoupper($cmd), @preg_match("#" . $cmd . "(.exe)?$#i", exec_cmdv($cmdv)) > 0);
+	// todo: cache all cmd tests
+	$cmd = false;
+	if (!$cmd && exec_0("command -v command")) {
+		$cmd = "command -v";
+	}
+	if (!$cmd && exec_0("which which")) {
+		$cmd = "which";
+	}
+	foreach (array("tar", "zip", "convert", "ffmpeg", "avconv", "du") as $c) {
+		define("HAS_CMD_" . strtoupper($c), ($cmd !== false) && exec_0($cmd . " " . $c));
 	}
 }
diff --git a/src/_h5ai/server/php/inc/util.php b/src/_h5ai/server/php/inc/util.php
index fc2d091f..4672bea8 100644
--- a/src/_h5ai/server/php/inc/util.php
+++ b/src/_h5ai/server/php/inc/util.php
@@ -96,6 +96,18 @@ function exec_cmdv($cmdv) {
 }
 
 
+function exec_0($cmd) {
+
+	$lines = array();
+	$rc = null;
+	try {
+		@exec($cmd, $lines, $rc);
+		return $rc === 0;
+	} catch (Exception $e) {}
+	return false;
+}
+
+
 
 /*********************************************************************
   Debug Tools