linux – How to Send stderr to stdout with Pipe

command linelinuxmakepipestdout

I'm trying to capture all of the output of a build operation, and send it to myprogram. I seem to only be able to capture part of it. This is what I'm trying:

make clean && make DISABLE_ID3TAG=1 CFLAGS="-O2 -DNDEBUG -W64" | myprogram &2 > 1

I also tried:

make clean && make DISABLE_ID3TAG=1 CFLAGS="-O2 -DNDEBUG -W64" &2 > 1 | myprogram

Basically I want to send everything to stdout and then do something with that. Currently I'm only capturing part of the output, and the other part is going to the screen. How can I pipe everything to another program?

Best Answer

Since you have two commands, it would be better to use:

{ make clean && make DISABLE_ID3TAG=1 CFLAGS="-O2 -DNDEBUG -W64"; } 2>&1 | myprogram

( make clean && make DISABLE_ID3TAG=1 CFLAGS="-O2 -DNDEBUG -W64" ) 2>&1 | myprogram

The make clean is not directing its output to the pipe, you will want to use either of the two above to let the shell redirect the output of both make calls as one.

Related Solutions

shell – How to Send stdout to Multiple Commands

You can use tee and process substitution for this:

cat file.txt | tee >(pbcopy) | grep errors

This will send all the output of cat file.txt to pbcopy, and you'll only get the result of grep on your console.

You can put multiple processes in the tee part:

cat file.txt | tee >(pbcopy) >(do_stuff) >(do_more_stuff) | grep errors

What is Meant by Connecting STDOUT and STDIN?

Standard input and standard output are not commands.

Imagine commands as machines in a factory with an assembly line. Most machines are designed to have one conveyor belt to feed data in and one conveyor belt to feed data out; they are the standard input and the standard output respectively. The standard error is an opening on the side of the machine where it can eject rejects.

+-------+     +------------------+       +------------------+     +------+
| input |     |    machine A     |       |    machine B     |     |output|
| reser |=====|<stdin     stdout>|=======|<stdin     stdout>|=====|bucket|
| ‑voir |  →  |      stderr      |   →   |      stderr      |  →  |      |
+-------+     +------------------+       +------------------+     +------+
                      ||                          ||

The diagram above shows a conveyor belt that goes through two machines. The data comes from the input reservoir on the left, is fed to machine A, then the output is conveyed further to machine B (for which it is input), and machine B's output is deposited in the output bucket on the right.

In unix terms, this is called a pipeline. The metaphor is that of plumbing: a pipe connects machine A to machine B. The shell syntax for the pipeline above is

<input-file.txt commandA | commandB >output-file.txt

The < redirection symbol tells the shell to connect commandA's standard input to the file input-file.txt before launching commandA. (You can put the redirection before or after the command name.) The > redirection symbol tells the shell to connect commandB's standard output to output-file.txt. The pipe ("|") symbol in the middle tells the shell to connect commandA's standard output to commandB's standard input before launching them.

Commands can have more than one input and more than one output, but that's material for another day.

Best Answer

Related Solutions

shell – How to Send stdout to Multiple Commands

What is Meant by Connecting STDOUT and STDIN?

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