CODEWITHSUNDEEP
linuxbash
alexandernst
alexandernst

Reputation: 15109

Bash: read stdin from file and write stdout to file

I'm trying to run an app (let's say top) so it will read from a file for stdin and write to another file from stdout.

Currently I have

mkfifo stdin.pipe
(tail -f stdin.pipe) | top

which works as expected, as I can then echo something to that file and top will receive it. But I'm unable to redirect the output of top. How can I achieve this?

EDIT:

Ok, let's scratch top. I'm testing with this:

cat test.sh

echo Say something
read something
echo you said $something

Upvotes: 17

Views: 70770

Answers (2)

Joni
Joni

Reputation: 111259

Is there a way I can map stdin and stdout to files and use them to control a cli app?

It sounds like you are looking for coprocesses, added to Bash in 4.0.

coproc cat                    # Start cat in background
echo Hello >&${COPROC[1]}     # Say "Hello" to cat
read LINE <&${COPROC[0]}      # Read response
echo $LINE                    # cat replied "Hello"!

Before 4.0 you had to use two named pipes to achieve this.

Upvotes: 8

cdarke
cdarke

Reputation: 44354

Let's forget about top, that appears to be a red herring.

To map stdin or stdout to files, you can use redirection:

some_program < input_file          # Redirects stdin

another_program > output_file      # Redirects stdout

or even:

yet_another  < input_file > output_file

Upvotes: 54

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