shell script: how to send stdout one place & stderr another?

BrianK · 09-20-2007, 04:02 PM

I have a script that dumps a bunch of stuff to a file (uids of all users). On occasion, it tries to id a user that doesn't exist & spits out an error message. That error message does not go into the file (which is good) because, I assume, it's being directed to stderr. Is there a way to send the normal stdout to a file & then stderr to /dev/null?

I know I can do something like 2>&1 to send both to the same place, but what if I want to separate?

syg00 · 09-20-2007, 04:58 PM

Always try the obvious; 2>/dev/null

BrianK · 09-20-2007, 05:46 PM

Quote:

Originally Posted by syg00

Always try the obvious; 2>/dev/null

well that sends stderr to /dev/null but what about stdout? My question is how to send stdout to one file & stderr to another.

./script >> file 2>/dev/null

does not work.

[KIA]aze · 09-20-2007, 06:08 PM

Does this work?:

Code:

./script 1>>file 2>/dev/null

Or without ">>"?:

Code:

./script 1>file 2>/dev/null

chrism01 · 09-20-2007, 07:21 PM

prog 1>prog.log 2>prog.err
if you want to be able to look at the error later, which I'd recommend... otherwise
prog 1>prog.log 2>/dev/null
if you don't care about the error

BrianK · 09-20-2007, 08:54 PM

Quote:

Originally Posted by chrism01

prog 1>prog.log 2>prog.err
if you want to be able to look at the rror later, which I'd recommend... otherwise
prog 1>prog.log 2>/dev/null
if you don't care about the error

hrm. That does work under bash, but not tcsh (I had tried this before on a hunch, but never tried it with bash).

If anyone knows if this is possible with [t]csh, I'd love to hear it, otherwise, I'll just re-write my script in bash.

Thanks for the tip!

chrism01 · 09-20-2007, 09:20 PM

Well, technically the '1' is optional as in if you just say
prog >prog.log
the shell assumes you meant stdout.
I've always been under the impression the the following holds true for all unix shells
stdin = 0
stdout = 1
stderr = 2
and that the re-direction I showed would work also..... I shall be interested to see an explanation of t/csh.

bigearsbilly · 09-21-2007, 05:06 AM

the csh and derivatives are inferior.

http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/

consider swapping shells.

makyo · 09-21-2007, 06:57 AM

Hi.

Quote:

Originally Posted by BrianK

hrm. That does work under bash, but not tcsh (I had tried this before on a hunch, but never tried it with bash).

If anyone knows if this is possible with [t]csh, I'd love to hear it, otherwise, I'll just re-write my script in bash.

Thanks for the tip!

Quote:

The shell cannot presently redirect diagnostic output without also
redirecting standard output, but `(command > output-file) >& error-
file' is often an acceptable workaround. Either output-file or error-
file may be `/dev/tty' to send output to the terminal.

-- excerpt from man tcsh, q.v.

I also strongly recommend using csh-family only for interactive use ... cheers, makyo