diff --git a/plugins/php/php-cgi b/plugins/php/php-cgi
index a761f9eb..0aa81748 100755
--- a/plugins/php/php-cgi
+++ b/plugins/php/php-cgi
@@ -32,5 +32,21 @@ echo 'php_processes.info The current number of php-cgi processes.'
 exit 0
 fi
 
+CMD_GREP=`which grep`
+if [ ! -e ${CMD_GREP} ]; then
+  echo "Command grep (${CMD_GREP}) not found!"
+  exit 1
+fi
+CMD_SED=`which sed`
+if [ ! -e ${CMD_SED} ]; then
+  echo "Command sed (${CMD_SED}) not found!"
+  exit 1
+fi
+CMD_WC=`which wc`
+if [ ! -e ${CMD_WC} ]; then
+  echo "Command wc (${CMD_WC}) not found!"
+  exit 1
+fi
+
 echo -n "php_processes.value "
-/bin/ps ax | /usr/bin/grep -i php-cgi | /usr/bin/grep -v grep | /usr/bin/wc -l | /usr/bin/sed 's/\t +//' | /usr/bin/sed 's/ *//'
+/bin/ps ax | ${CMD_GREP} -i php-cgi | ${CMD_GREP} -v grep | ${CMD_WC} -l | ${CMD_SED} 's/\t +//' | ${CMD_SED} 's/ *//'