What is the -ex option in bash | #! / bin / bash -ex means

Question

We use the script below as user data for EC2 instances. I do not understand what the -ex option is used for?

 #!/bin/bash -ex yum update -y yum groupinstall -y "Web Server" "MySQL Database" "PHP Support" service httpd start chkconfig httpd on 

Answer 1

This is just another way of saying:

 #!/bin/bash set -ex # Added line yum update -y yum groupinstall -y "Web Server" "MySQL Database" "PHP Support" service httpd start chkconfig httpd on 

[bash manual] says:

All single-character parameters used with the built-in set (see Set Builtin) can be used as options when invoking the shell

[set reference] says:

allows you to change shell parameter values ​​and set positional parameters or display variable shell names and values.

-x

Print a trace of simple commands, commands, case commands, select commands and arithmetic for commands and their arguments or related word lists after they are expanded and before they are executed. The value of the PS4 variable is expanded, and the result of the value is displayed before the command and its extended arguments.

-e

Exit immediately if the pipeline (see Pipelines), which can consist of a single simple command (see Simple commands), a list (see Lists), or a compound command (see compound commands) returns a non-zero status.

Answer 2

A good article that answers the question: “Add sticky notes to your bash shebang | #! / Bin / bash -ex" https://scottlinux.com/2014/08/05/add-tack-ex-on-your-bash -shebang-binbash-ex /

Bash scripts can use various parameters in shebang (#! / Bin / bash). more general: "#! / bin / bash -ex.

-e Exit immediately if the command exits with a non-zero status. -x Print commands and their arguments as they execute.

In short, adding -ex to your #! / Bin / bash will give verbose output and also abort your script immediately if the script part is not executed.