How can I send the stdout of one process to multiple processes using (preferably unnamed) pipes in Unix (or Windows)?

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

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

$ echo 123 | tee >(tr 1 a)  | tr 1 b
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

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.

Answer 2

Look into the tee command.

Answer 3

Since @dF: mentioned that PowerShell has tee, I thought I'd show a way to do this in PowerShell.

PS > "123" | % { 
    $_.Replace( "1", "a"), 
    $_.Replace( "2", "b" ) 
}

a23
1b3

Note that each object coming out of the first command is processed before the next object is created. This can allow scaling to very large inputs.