What does `set -x` do?

I have a shell script with the following line in it:

[ "$DEBUG" == 'true' ] && set -x

set -x enables a mode of the shell where all executed commands are printed to the terminal. In your case it's clearly used for debugging, which is a typical use case for set -x: printing every command as it is executed may help you to visualize the control flow of the script if it is not functioning as expected.

set +x disables it.

set -x

> Prints a trace of simple commands, for commands, case commands, select > commands, and arithmetic for commands and their arguments or > associated word lists after they are expanded and before they are > executed. The value of the PS4 variable is expanded and the resultant > value is printed before the command and its expanded arguments.

[source]

Example

set -x
echo `expr 10 + 20 `
+ expr 10 + 20
+ echo 30
30

---

set +x
echo `expr 10 + 20 `
30

Above example illustrates the usage of set -x. When it is used, above arithmetic expression has been expanded. We could see how a single line has been evaluated step by step.

• First step expr has been evaluated.
• Second step echo has been evaluated.

To know more about set → visit this link

when it comes to your shell script,

[ "$DEBUG" == 'true' ] && set -x

Your script might have been printing some additional lines of information when the execution mode selected as DEBUG. Traditionally people used to enable debug mode when a script called with optional argument such as -d

> -u: disabled by default. When activated, an error message is displayed when using an unconfigured variable. > > -v: inactive by default. After activation, the original content of the information will be displayed (without variable resolution) before the > information is output. > > -x: inactive by default. If activated, the command content will be displayed before the command is run (after variable resolution, there > is a ++ symbol).

Compare the following differences:

/ # set -v && echo $HOME
/root
/ # set +v && echo $HOME
set +v && echo $HOME
/root

/ # set -x && echo $HOME
+ echo /root
/root
/ # set +x && echo $HOME
+ set +x
/root

/ # set -u && echo $NOSET
/bin/sh: NOSET: parameter not set
/ # set +u && echo $NOSET

Instead of giving set -x and set +x , we can run script using -x Example : ksh -x script_name.ksh Please correct me or enhance my knowledge if I'm wrong