redirect all output in a bash script when using set -x

Question

I have a bash script that has set -x in it. Is it possible to redirect the debug prints of this script and all its output to a file? Ideally I would like to do something like this:

#!/bin/bash
set -x
(some magic command here...) > /tmp/mylog
echo "test"

and get the

+ echo test
test

output in /tmp/mylog, not in stdout.

Answer 1

This is what I've just googled and I remember myself using this some time ago...

Use exec to redirect both standard output and standard error of all commands in a script:

#!/bin/bash logfile=$$.log exec > $logfile 2>&1 

For more redirection magic check out Advanced Bash Scripting Guide - I/O Redirection.

If you also want to see the output and debug on the terminal in addition to in the log file, see redirect COPY of stdout to log file from within bash script itself.

If you want to handle the destination of the set -x trace output independently of normal STDOUT and STDERR, see bash storing the output of set -x to log file.

Answer 2

the -x output goes to stderr, so to log it do:

set -x exec 2>/tmp/mylog 

Answer 3

In my case, the script was being called multiple times from elsewhere, and I wasn't seeing everything, so I did an append instead, and it worked:

exec 1>>FILENAME 2>&1
set -x

To avoid confusion, be sure to delete FILENAME before each run.