Question

I’d like to redirect the stdout of process proc1 to two processes proc2 and proc3:

         proc2 -> stdout        /  proc1        \           proc3 -> stdout 

I tried

 proc1 | (proc2 & proc3) 

but it doesn’t seem to work, i.e.

 echo 123 | (tr 1 a & tr 1 b) 

writes

 b23 

to stdout instead of

 a23  b23 

Answer 1

^{Editor’s note:
– >(…) is a process substitution that is a nonstandard shell feature of some POSIX-compatible shells: bash, ksh, zsh.
– This answer accidentally sends the output process substitution’s output through the pipeline too: echo 123 | tee >(tr 1 a) | tr 1 b.
– Output from the process substitutions will be unpredictably interleaved, and, except in zsh, the pipeline may terminate before the commands inside >(…) do.}

In unix (or on a mac), use the tee command:

$ echo 123 | tee >(tr 1 a) >(tr 1 b) >/dev/null b23 a23 

Usually you would use tee to redirect output to multiple files, but using >(…) you can redirect to another process. So, in general,

$ proc1 | tee >(proc2) ... >(procN-1) >(procN) >/dev/null 

will do what you want.

Under windows, I don’t think the built-in shell has an equivalent. Microsoft’s Windows PowerShell has a tee command though.