innobackupex - get output from command line

innobackupex - get output from command line

I'm running the innobackupex script, but I don't know how to fetch the
output from the script? I need the last line to check if the script
succeeded or failed..
$output = shell_exec('innobackupex --user=root --password=xxx
--databases="test" --stream=tar ./ | gzip -c -1 >
/var/bak/2013-08-09-1431_mysql.tar.gz')
The script is working as it should and the backup zip is created...