Redirect terminal output to file

Question

I am looking for a bash command where I can redirect:

1. stdout of a command to a file
2. stderr to both that file and the console.

I have found ways where the stderr will append to the end of the file after the stdout, but I want it so that the output file orders all out the output chronologically like it would if I were to just use command &> file.

I have tried:

command 2>&1 1>logfile | tee -a logfile
command 2> >(tee -a logfile) 1>>logfile

I would basically like the output file to be same as if I simply did command &> logfile, whilst at the same time keep printing stderr messages to the console.

Answer 1

Let's create a test function that sends some output to both stdout and stderr:

$ cmd() { echo 1 on stdout; echo 2 on stderr >&2; echo 3 on stdout; echo 4 on stderr >&2; }

Running it we see:

$ cmd
1 on stdout
2 on stderr
3 on stdout
4 on stderr

Now, we want to send the stdout to a file, and the stderr to both the file and the screen. For this we use a simple redirection for stdout, and for stderr we redirect into a process substitution that appends to the file and sends the output back to stderr:

$ cmd > cmd.out 2> >( tee -a cmd.out >&2 )
2 on stderr
4 on stderr

$ cat cmd.out
1 on stdout
3 on stdout
2 on stderr
4 on stderr

I do not know of a way to keep the chronological order of the intermixed stdout and stderr messages.

Answer 2

It works if you append stdout to the file and redirect stderr to tee, also appending to the file:

$ bash -c "echo a;bahs;echo b;bhas" >>file 2> >( tee -a file >&2 )
bash: bahs: command not found
bash: bhas: command not found
$ cat file
a
bash: bahs: command not found
b
bash: bhas: command not found

This doesn’t work with the test from glenn jackman’s answer and I can’t wrap my head around why.

Answer 3

I don't think you can really do that.

When you redirect stdout and stderr separately, they become unsynchronized, and there's no way to fix them back again. What you're trying to do is something like this:

                  +------> terminal
                  |       
cmd -(stderr)--> tee ----> file
 |                          ^
 +---(stdout)---------------+      

Here, there are two parallel paths from cmd to file, with an additional process in the stderr path. Depending on the scheduling, there might be delays in the path that involves tee, which can and will lead to the stderr messages being delayed.

To prevent that, the system would need to switch to tee immediately when it gets input. Usually, it can't be counted on to do that. Adding another process to the parallel path won't help, as then the result will just depend on the scheduling between the two intermediate processes (instead of cmd and tee).

Answer 4

You can do something like this:

echo "asd" | xargs -I % sh -c 'echo % && echo % > asd'

First echo is passed to xargs which takes it as argument and build two echo's commands, first result is output to terminal and second to file named also asd as the text.

You can put the redirects after in order to match your needs.