Bash – How to Direct Output to Pipe and Stdout

bashpipestdouttee

I was wondering if there is a way to pipe the output of a command and direct it to the stdout. So for example, fortune prints a fortune cookie and also copies it to the clipboard: 

$ fortune | tee >(?stdout?) | pbcopy 
"...Unix, MS-DOS, and Windows NT (also known as the Good, the Bad, and
the Ugly)."
(By Matt Welsh)

Best Answer

Your assumption:

fortune | tee >(?stdout?) | pbcopy

won't work because the fortune output will be written to standard out twice, so you will double the output to pbcopy.

In OSX (and other systems support /dev/std{out,err,in}), you can check it:

$ echo 1 | tee /dev/stdout | sed 's/1/2/'
2
2

output 2 twice instead of 1 and 2. tee outputs twice to stdout, and tee process's stdout is redirected to sed by the pipe, so all these outputs run through sed and you see double 2 here.

You must use other file descriptors, example standard error through /dev/stderr:

$ echo 1 | tee /dev/stderr | sed 's/1/2/'
1
2

or use tty to get the connected pseudo terminal:

$ echo 1 | tee "$(tty)" | sed 's/1/2/'
1
2

With zsh and multios option set, you don't need tee at all:

$ echo 1 >/dev/stderr | sed 's/1/2/'
1
2
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