How can I redirect the output of a child process?

Question

I am running the following git clone command through sudo and bash and I want to redirect STDOUT to a log file:

% sudo -u test_user bash -c "git clone https://github.com/scrooloose/nerdtree.git
/home/test_user/.vim/bundle/nerdtree >> /var/log/build_scripts.log"

What is happening is the STDOUT is continuing to be sent to the terminal. i.e.

Cloning into 'nerdtree'...
remote: Counting objects: 3689, done.
[...]
Checking connectivity... done.

I'm guessing the problem has something to do with the fact that sudo is forking a new process then bash is forking another, as demonstrated here:

% sudo -u test_user bash -c "{ git clone https://github.com/scrooloose/nerdtree.git
/home/test_user/.vim/bundle/nerdtree >> /var/log/build_scripts.log; ps f -g$$; }"  

  PID TTY      STAT   TIME COMMAND
 6556 pts/25   Ss     0:02 /usr/bin/zsh
 3005 pts/25   S+     0:00  \_ sudo -u test_user bash -c { git clone https://github.com/scrooloo
 3006 pts/25   S+     0:00      \_ bash -c { git clone https://github.com/scrooloose/nerdtree.
 3009 pts/25   R+     0:00          \_ ps f -g6556

I've tried

• running this in a script and using exec >> /var/log/build_script.log before the command
• wrapping the command in a function, then calling and redirecting the functions output

But I think these redirections are only applying to the parent and the child processes are defaulting to sending STDOUT to the /dev/tty/25 of their parent causing output to continue to the terminal.
How can I redirect the STDOUT of this command?

Answer 1

The messages you mention are not printed to standard output but to standard error. So, to capture them, you either need to redirect standard error instead of standard output:

sudo -u user bash -c "git clone https://github.com/foo.git ~/foo 2>> log"

Or both STDERR and STDOUT:

sudo -u user bash -c "git clone https://github.com/foo.git ~/foo >> log 2>&1"

With bash, you can also use &>> for this:

sudo -u user bash -c "git clone https://github.com/foo.git ~/foo &>> log"

The csh, tcsh, zsh equivalent being >>& ((t)csh don't support 2>&1 so it's the only way there):

sudo -u user csh -c "git clone https://github.com/foo.git ~/foo >>& log"

In fish

sudo -u user fish -c "git clone https://github.com/foo.git ~/foo >> log ^&1"

For more on the different types of redirection operators, see What are the shell's control and redirection operators?

Now, in the specific case of git, there's another issue. Like a few other programs, git can detect that its output is being redirected and stops printing progress reports if so. This is probably because the reports are intended to be seen live and include \r which can be a problem when saved in a file. To get around this, use:

       --progress
       Progress status is reported on the standard error stream by default
       when it is attached to a terminal, unless -q is specified. This
       flag forces progress status even if the standard error stream is
       not directed to a terminal.

And:

sudo -u user bash -c "git clone --progress https://github.com/foo.git ~/foo >> log 2>&1"

If you want to both see the output as it comes and save to a file, use tee:

sudo -u user bash -c "git clone --progress https://github.com/foo.git ~/foo 2>&1 | 
    tee -a log

Answer 2

git clone https://github.com/scrooloose/nerdtree.git
/home/test_user/.vim/bundle/nerdtree &>> /var/log/build_scripts.log