Redirect stderr and stdout in Bash

Question

I want to redirect both stdout and stderr of a process to a single file. How do I do that in Bash?

Answer 1

I wanted a solution to have the output from stdout plus stderr written into a log file and stderr still on console. So I needed to duplicate the stderr output via tee.

This is the solution I found:

command 3>&1 1>&2 2>&3 1>>logfile | tee -a logfile

• First swap stderr and stdout
• then append the stdout to the log file
• pipe stderr to tee and append it also to the log file

Answer 2

Take a look here. Should be:

yourcommand &>filename

(redirects both stdout and stderr to filename).

Answer 3

In situations when you consider using things like exec 2>&1 I find easier to read if possible rewriting code using bash functions like this:

function myfunc(){
  [...]
}

myfunc &>mylog.log

Answer 4

For tcsh, I have to use the following command :

command >& file

If use command &> file , it will give "Invalid null command" error.

Answer 5

@fernando-fabreti

Adding to what you did I changed the functions slightly and removed the &- closing and it worked for me.

    function saveStandardOutputs {
      if [ "$OUTPUTS_REDIRECTED" == "false" ]; then
        exec 3>&1
        exec 4>&2
        trap restoreStandardOutputs EXIT
      else
          echo "[ERROR]: ${FUNCNAME[0]}: Cannot save standard outputs because they have been redirected before"
          exit 1;
      fi
  }

  # Params: $1 => logfile to write to
  function redirectOutputsToLogfile {
      if [ "$OUTPUTS_REDIRECTED" == "false" ]; then
        LOGFILE=$1
        if [ -z "$LOGFILE" ]; then
            echo "[ERROR]: ${FUNCNAME[0]}: logfile empty [$LOGFILE]"
        fi
        if [ ! -f $LOGFILE ]; then
            touch $LOGFILE
        fi
        if [ ! -f $LOGFILE ]; then
            echo "[ERROR]: ${FUNCNAME[0]}: creating logfile [$LOGFILE]"
            exit 1
        fi
        saveStandardOutputs
        exec 1>>${LOGFILE}
        exec 2>&1
        OUTPUTS_REDIRECTED="true"
      else
        echo "[ERROR]: ${FUNCNAME[0]}: Cannot redirect standard outputs because they have been redirected before"
          exit 1;
      fi
  }
  function restoreStandardOutputs {
      if [ "$OUTPUTS_REDIRECTED" == "true" ]; then
      exec 1>&3   #restore stdout
      exec 2>&4   #restore stderr
      OUTPUTS_REDIRECTED="false"
     fi
  }
  LOGFILE_NAME="tmp/one.log"
  OUTPUTS_REDIRECTED="false"

  echo "this goes to stdout"
  redirectOutputsToLogfile $LOGFILE_NAME
  echo "this goes to logfile"
  echo "${LOGFILE_NAME}"
  restoreStandardOutputs 
  echo "After restore this goes to stdout"

Answer 6

do_something 2>&1 | tee -a some_file

This is going to redirect stderr to stdout and stdout to some_file and print it to stdout.