how to append stderr?

mathfeel · 06-15-2006, 05:30 PM

I know that > and >& writes stdout and stdout+stderr to a file, respetively.
I also know that >> appends stdout to a file.
Is there a similar thing for appending stdout+stderr? Thanks

zhangmaike · 06-15-2006, 06:21 PM

The only way I can think of:

Code:

(insert_command_here 2>&1) >> some_file

The 2>&1 will redirect stderr to stdout, and >> will append stdout (which is also stderr because of the previous redirection) to some_file.

mathfeel · 06-16-2006, 12:41 AM

Quote:

Originally Posted by zhangmaike

The only way I can think of:

Code:

(insert_command_here 2>&1) >> some_file

The 2>&1 will redirect stderr to stdout, and >> will append stdout (which is also stderr because of the previous redirection) to some_file.

I saw lots of sample code with 1 and 2, never understood what they mean. So 1 means stdout, 2 means stderr?

zhangmaike · 06-16-2006, 01:05 AM

Output redirection involves the manipulation of file descriptors, which are themselves numbers.

Redirecting output from stdout/stderr to stderr/stdout/a file merely changes which file descriptor is being used.

stdin is file descriptor 0
stdout is file descriptor 1
stderr is file descriptor 2

Quote:

So 1 means stdout, 2 means stderr?

Yes.

If you're interested, there is a huge section on redirection in the bash manpage which covers not only this sort of redirection, but also redirection to/from hosts through tcp or udp ports.