13.5 Redirection in C Shell: Capture Errors, Too?

The > (right angle bracket) operator redirects the standard output of a process to a file. It doesn't affect the standard error. If you're logged in and can see any messages written to standard error, that's okay:

% 

nroff -ms report.ms > report.out &


[1] 10316
   ...
Later
...
nroff: can't open file /hoem/jpeek/report.data

But if you log out and leave the job running, you'll never see those errors unless you use the csh operator >& . It redirects both standard output and standard error to a file. For example:

make
 

% 

make >& make.output &


[1] 10329
% 

logout


   ...
Later
...
% 

cat make.output


        cc -O -c random.c
        cc -O -c output.c
"output.c", line 46: syntax error
"output.c", line 50: time_e undefined
"output.c", line 50: syntax error
   ...

You might also use the >& operator while you're logged in - and watch the output file with tail -f ( 25.16 ) . If you don't want the errors mixed with other output, you can split them to two files; see article 13.1 .

The C shell also has a pipe operator, |& , that redirects both standard output and standard error. It's great for running a job in the background, or on another computer, and mailing ( 1.33 ) any output to me:

% 

make |& mailx -s "'make bigprog' output" jpeek@jpeek.com &


[1] 29182 29183

If I'd used plain | instead of |& , any text on the standard error wouldn't go into the mail message.