$ ack test
ack: launchd-876.k0GsfA: Permission denied
ack: launchd-898.YkvjEN: Permission denied
teste
1:1:testing
2:1:teste
$ ack -s test
ack: launchd-876.k0GsfA: Permission denied
ack: launchd-898.YkvjEN: Permission denied
teste
1:1:testing
2:1:teste
$ grep test * 2 ↵
grep: 20140312135345: Is a directory
grep: Alfred2: Is a directory
grep: atom-compile-cache: Is a directory
grep: launch-XPgUtW: Is a directory
grep: launch-xgV9Gb: Is a directory
grep: launchd-245.FQ1mEN: Is a directory
grep: launchd-876.k0GsfA: Permission denied
grep: launchd-898.YkvjEN: Permission denied
grep: mysql.sock: Operation not supported on socket
teste:testing
teste:teste
grep: tmp: Is a directory
xpto:test
xpto:testing
$ grep -s test *
teste:testing
teste:teste
xpto:test
xpto:testing