our hero: set -x

set -x prints out every line of a script as it executes, with all the variables expanded!

#!/bin/bash set -x (I usually put set -x at the top)

or bash -X

$ bash -x script.sh does the same thing as putting set -x at the top of script.sh

you can stop before every line

trap read DEBUG
the DEBUG “signal” is triggered before every line of code

a fancy step debugger trick

put this at the start of your script to confirm every line before it runs:

trap '(read -p "\[$BASH_SOURCE: $LINENO] $BASH_COMMAND")' DEBUG

• read -p prints a message, press enter to continue
  
• $BASH_SOURCE is the script filename
  
• $LINENO is the line number
• $BASH_COMMAND is the next command that will run

how to print better error messages

this die function: die() { echo $1 >&2; exit 1; } lets you exit the program and print a message if a command fails, like this: some_command || die "oh no!"