Bash – How to debug a bash script

bashdebugging

I'm having some problems with some scripts in bash, about errors and unexpected behaviors. I would like to investigate the causes of the problems so I can apply fixes. Is there a way I can turn some kind of "debug-mode" for bash, to get more information?

Best Answer

Start your bash script with bash -x ./script.sh or add in your script set -x to see debug output.

Additional with bash 4.1 or later:

If you want to write the debug output to a separate file, add this to your script:

exec 5> debug_output.txt
BASH_XTRACEFD="5"

See: https://stackoverflow.com/a/25593226/3776858

If you want to see line numbers add this:

PS4='$LINENO: '

If you have access to logger command then you can use this to write debug output via your syslog with timestamp, script name and line number:

#!/bin/bash

exec 5> >(logger -t $0)
BASH_XTRACEFD="5"
PS4='$LINENO: '
set -x

# Place your code here

You can use option -p of logger command to set an individual facility and level to write output via local syslog to its own logfile.

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