How can I redirect `time` output and command output to the same pipe?

Question

Suppose I have a binary called foo.

If I want to redirect the output of foo to some other process bar, I could write ./foo | bar.

On the other hand, if I wanted to time foo, and redirect the output of time I could write, time (./foo) | bar.

My question is, how can I stick the output of time to the end of the output of foo and pipe it through the same pipe?

The following solution is not what I am looking for, because it starts two separate instances of the process bar, while I want a single shared pipe, to a single instance of bar.

time (./foo | bar) | bar 

For anyone who is curious, the reason for not wanting to start two instances of bar is because bar can be a network client and I want the timing information to be sent to the server as part of the same http POST message as the process output.

Answer 1

If I understand what you're asking for I this will do. I'm using the commands ls ~ and tee as stand-ins for ./foo and bar, but the general form of what you want is this:

$ ( time ./foo ) |& bar 

NOTE: The output of time is already being attached at the end of any output from ./foo, it's just being done so on STDERR. To redirect it through the pipe you need to combine STDERR with STDOUT. You can use either |& or 2>&1 to do so.

$ ( time ./foo ) |& bar -or- $ ( time ./foo ) 2>&1 | bar 

Example

$ ( time ls . ) |& tee cmd.log cmd.log file1 file2 file3 file4 file5 real 0m0.005s user 0m0.000s sys 0m0.001s 

And here's the contents of the file cmd.log produced by tee.

$ more cmd.log cmd.log file1 file2 file3 file4 file5 real 0m0.005s user 0m0.000s sys 0m0.001s 

Answer 2

time sends its output to stderr instead of stdout by default. You just need to redirect that where you want it.

You say "On the other hand, if I wanted to time foo, and redirect the output of time I could write, time (./foo) | bar." but this is actually incorrect. In this case, the output of time would still be displayed on your console, only stdout would be redirected.

You can redirect stderr specifically with:

(time foo) 2>&1 | bar 

or all pipes with:

(time foo) |& bar 

The brackets are needed for this to work correctly.

Answer 3

I found that this works on Solaris. (time ls) &> file