CODEWITHSUNDEEP
bashstdoutstderr
dancow
dancow

Reputation: 3388

Bash: How to direct output to both stderr and to stdout, to pipe into another command?

I know variations of this question have been asked and answered several times before, but I'm either misunderstanding the solutions, or am trying to do something eccentric. My instinct is that it shouldn't require tee but maybe I'm completely wrong...

Given a command like this:

sh
echo "hello"

I want to send it to STDERR so that it can be logged/seen on the console, and so that it can be sent to another command. For example, if I run:

sh
echo "hello" SOLUTION>&2 > myfile.txt

(SOLUTION> being whatever the answer to my problem is)

I want:

Upvotes: 0

Views: 159

Answers (2)

Barmar
Barmar

Reputation: 780655

There's no need to redirect it to stderr. Just use tee to send it to the file while also sending to stdout, which will go to the terminal.

echo "hello" | tee myfile.txt

If you want to pipe the output to another command without writing it to a file, then you could use

echo "hello" | tee /dev/stderr | other_command

You could also write a shell function that does the equivalent of tee /dev/stderr:

$ tee_to_stderr() {
    while read -r line; do
        printf "%s\n" "$line";
        printf "%s\n" "$line" >&2
    done
}

$ echo "hello" | tee_to_stderr | wc
hello
       1       1       6

This doesn't work well with binary output, but since you intend to use this to display text on the terminal that shouldn't be a concern.

Upvotes: 3

John Kugelman
John Kugelman

Reputation: 361547

tee copies stdin to the files on its command line, and also to stdout.

echo hello | tee myfile.txt >&2

This will save hello in myfile.txt and also print it to stderr.

Upvotes: 1

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