How to copy standard output and standard error to the log?

Question

I need to write the standard err and standard output to $LOG, while also having them printed on console, from within a script.

The script has many commands, so redirecting each one of them is not a good solution.

I've tried this, but it didn't work as expected:

#!/bin/bash

LOG=/var/tmp/log

#...

exec > $LOG  2>&1

My target is to write to $LOG on any standard output and standard error, but on the same time also to the standard output (on console). Is it possible?

Answer 1

Use tee. For example:

command 2>&1 | tee file.txt

Which runs command redirecting SDTERR to SDTOUT. tee copies STDIN to both STDOUT and to file file.txt.

In bash you can use process substitution in following way to copy output to $LOG:

exec &> >(tee $LOG)

However this bashism won't work on other shells.

Answer 2

I'm not sure if this is the most clean solution but it worked for me:

#!/bin/bash

LOG=/var/tmp/log

(
# lots of commands
# ...

) 2>&1 | tee $LOG

@sebasth gave a better solution, though:

#!/bin/bash

LOG=/var/tmp/log

exec &> >(tee $LOG)

#...