A vertical bar character (
|
) on a command line pipes the standard output of a process to another process. How can you pipe the standard error, not the standard output? You might want to put a long-running
cruncher
command in the background, save the output to a file, and mail yourself a copy of the errors. In the C shell, run the command in a
subshell (
13.7
)
. The standard output of the command is redirected inside the subshell. All that's left outside the subshell is the standard error; the
|&
operator (
13.5
)
redirects it (along with the empty standard output) to the
mail
(
1.33
)
program:
%(cruncher >
outputfile
yourname
& [1] 12345
Of course, you don't need to put that job
in the background (
1.26
)
. If you want the standard output to go to your terminal instead of a text file, use
/dev/tty
(
45.20
)
as the
outputfile
.
The Bourne shell gives you a lot more flexibility and lets you do just what you need. The disadvantage is the more complicated syntax ( 45.21 ) . Here's how to run your cruncher program, route the stderr through a pipe to the mail program, and leave stdout going to your screen:
$(cruncher 3>&1 1>&2 2>&3 3>&-) | mail
yourname
&
12345
To redirect stdout to an output file and send stderr down a pipe, try this:
$(cruncher 3>&1 >
outputfile
2>&3 3>&-) | mail
yourname
&
12345
-