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I have a script that outputs text to stdout. I want to see all this output in my terminal, and at the same time I want to filter some lines and save them in a file. Example:

$ myscript
Line A
Line B
Line C

$ myscript | grep -P 'A|C' > out.file

$ cat out.file
Line A
Line C

I want to see output of first command in terminal, and save the output of the second command in a file. At the same time. I tried using tee, but with no result, or better, with reversed result.

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3 Answers 3

up vote 8 down vote accepted

I want to see output of first command in terminal, and save the output of the second command in a file.

As long as you don't care whether what you are looking at is from stdout or stderr, you can still use tee:

myscript | tee /dev/stderr | grep -P 'A|C' > out.file

Will work on linux; I don't know if "/dev/stderr" is equally applicable on other *nixes.

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Nice trick! It works, thanks! –  lorenzo-s Apr 6 '13 at 19:06
/dev/stderr is common. /dev/tty (meaning the current terminal) would also work here, and it's standard. –  Gilles Apr 6 '13 at 23:42
@Gilles: Wonderful. tee /dev/tty served wonderfully for my requirement of having to print the stdout of a script to terminal and to pipe it to the stdin of another command as well! Thankees! :-) –  jamadagni Jun 7 '14 at 1:09
{ ... | tee /dev/fd/3 | grep -e A -e C > out.file; } 3>&1

Or with process substitution (ksh93, zsh or bash):

... | tee >(grep -e A -e C > out.file)

With zsh:

... >&1 > >(grep -e A -e C > out.file)
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you didn't specify how you used the tee command but this should work:

myscript | grep -P 'A|C' | tee out.file

at least it worked on my server few minutes ago...

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But, if I'm not wrong, this way you grep also what's on screen. I want to see all output on screen, and filter only what's going into the file. –  lorenzo-s Apr 6 '13 at 19:03

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