Hi Everyone!

This is an easy one for those with long time scripting in BASH or any of the other shells.

I know that the ">" redirects output to the next parameter but what about in a case like this? This is in a CRON job BTW

php cmd.php > /dev/null 2>&1

So far I understand that php runs cmd.php and then any resulting output is sent to /dev/null (ie. go bye bye) but what's the last set of args for?

I suppose that this is to keep the user account running this scron job from getting bombarded with cron run results but could there be more?

There are two output streams from a program:

stdout (filedescriptor 1, normal output)
stderr (filedescriptor 2, error mesages output)

and one input stream: stdin (filedescriptor 0)

$php cmd.php >/dev/null
would make all normal output disappear, but errormessages are still output.

stdout i on filedescriptor 1, so you could use 1>/dev/null as well.

$php cmd.php 2>/dev/null
would make all errormessages disappear, but all normal output would still be there.

$php cmd.php > /dev/null 2>&1
will output nothing at all: first stdout (which is on filedescriptor 1) is redirected to a file (/dev/null in this case to make ik disappear).
Then filedescriptor 2 (stderr, error messages) is redirected to the same place as stdin (1).

So, in brief:
"2>&1" means more or less: "Make error messages go where the normal output is going"

Note you cannot change the order: "2>&1 > /dev/null" will not work the same way. You can however make normal output go to one_file and error messages to another_file:

$php cmd.php >one_file.txt 2>another_file.txt

Here the order is not important, only in the special case of "2>&1".

Fantastic.

I knew there'd be someone who could regurgitate that easily! Thanks!