Shebang hack

The shebang can be changed from #!/bin/bash to #!/bin/bash -xv to enable debugging without any additional flags (-xv flags themselves).

It can be hard to track execution flow in the default output when each line is preceded by +. Set the PS4 environment variable to '$LINENO:' to display actual line numbers:

PS4='$LINENO: ' 

The debugging output may be long. When using -x or set -x, the debugging output is sent to stderr. It can be redirected to a file with the following command:

sh -x testScript.sh 2> debugout.txt

Bash 4.0 and later support using a numbered stream for debugging output:

exec 6> /tmp/debugout.txt 
BASH_XTRACEFD=6