How to redirect output to a file and stdout

The command you want is named tee:

foo | tee output.file

For example, if you only care about stdout:

ls -a | tee output.file

If you want to include stderr, do:

program [arguments...] 2>&1 | tee outfile

2>&1 redirects channel 2 (stderr/standard error) into channel 1 (stdout/standard output), such that both is written as stdout. It is also directed to the given output file as of the tee command.

Furthermore, if you want to append to the log file, use tee -a as:

program [arguments...] 2>&1 | tee -a outfile

Using tail -f output should work.

You can do that for your entire script by using something like that at the beginning of your script :

#!/usr/bin/env bash

test x$1 = x$'\x00' && shift || { set -o pipefail ; ( exec 2>&1 ; $0 $'\x00' "$@" ) | tee mylogfile ; exit $? ; }

# do whaetever you want

This redirect both stderr and stdout outputs to the file called mylogfile and let everything goes to stdout at the same time.

It is used some stupid tricks :

• use exec without command to setup redirections,
• use tee to duplicates outputs,
• restart the script with the wanted redirections,
• use a special first parameter (a simple NUL character specified by the $'string' special bash notation) to specify that the script is restarted (no equivalent parameter may be used by your original work),
• try to preserve the original exit status when restarting the script using the pipefail option.

Ugly but useful for me in certain situations.

In my case I had the Java process with output logs. The simplest solution to display output logs and redirect them into the file(named logfile here) was:

my_java_process_run_script.sh |& tee logfile

Result was Java process running with output logs displaying and putting them into the file with name logfile

< command > |& tee filename # this will create a file "filename" with command status as a content, If a file already exists it will remove existed content and writes the command status.

< command > | tee >> filename # this will append status to the file but it doesn't print the command status on standard_output (screen).

I want to print something by using "echo" on screen and append that echoed data to a file

echo "hi there, Have to print this on screen and append to a file" 

tee is perfect for this, but this will also do the job

ls -lr / > output | cat output