Setting the -x tells Bash to print out the statements as they are being executed. It can be very useful as a logging facility and for debugging when you need to know which statements were execute and in what order.

It can be enabled on the command line or on the sh-bang line by providing -x or by the set -x statement.

It can be disabled using the set +x statement.

See this example:

examples/shell/set-x.sh

#!/bin/bash -x

name="Foo"
echo $name

set +x

age=42
echo $age


set -x

language=Bash
echo $language

and the output it generates: 

$ ./examples/shell/set-x.sh

+ name=Foo
+ echo Foo
Foo
+ set +x
42
+ language=Bash
+ echo Bash
Bash