Debugging with PS4 in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the PS4 variable in bash scripting?

PS4 is a special variable in bash that defines the prompt used when debugging with 'set -x'. It helps show detailed trace information for each command executed.

beginner

How do you enable debugging mode in a bash script to see command traces?

You enable debugging by running 'set -x' in the script or shell. This makes bash print each command and its arguments before executing them.

intermediate

How can you customize the debugging output prefix using PS4?

You can set PS4 to any string you want. For example, 'PS4="+ $(date +%T) "' adds a timestamp before each debug line, making it easier to follow.

intermediate

What does the following PS4 value do? PS4='+ ${BASH_SOURCE}:${LINENO}:${FUNCNAME[0]}: '

This PS4 setting shows the script file name, line number, and function name before each debug line. It helps locate where commands run in the script.

beginner

How do you turn off debugging mode after using 'set -x'?

You turn off debugging by running 'set +x'. This stops bash from printing commands before execution.

What does the PS4 variable control in bash debugging?

A The error message format

B The shell prompt when not debugging

C The output color of the script

D The prompt shown before each debug command trace

PS4 sets the prefix shown before each command line when debugging with 'set -x'.

Which command enables debugging mode in bash?

A debug on

B set +x

C set -x

D trace enable

'set -x' turns on debugging, showing commands as they run.

How can you add a timestamp to each debug line in bash?

A Set PS4 to include $(date +%T)

B Use set +x with a timestamp

C Change the shell prompt PS1

D Use echo before each command

Setting PS4 to '+ $(date +%T) ' adds a timestamp prefix to debug output.

What does 'set +x' do in a bash script?

A Starts debugging mode

B Stops debugging mode

C Prints all variables

D Runs the script silently

'set +x' disables debugging mode and stops printing commands.

Which PS4 setting helps show the script file and line number in debug output?

A PS4='+ ${BASH_SOURCE}:${LINENO} '

B PS4='DEBUG>'

C PS4='Line:'

D PS4='${FUNCNAME[0]}'

Using '${BASH_SOURCE}:${LINENO}' in PS4 shows the file and line number for each command.

Explain how to use PS4 and set -x together to debug a bash script with detailed trace information.

Think about how PS4 changes the prefix and set -x turns on tracing.

Describe how you would stop debugging output after enabling it with set -x in a bash script.

Consider the opposite of set -x.