I want to force output when CentOS 7 error is not standard output

Based on the communication in the comments, what I really want to do is answer with the assumption that ifup I want to detect and receive any errors during execution.

In addition to the ifup command, Linux commands typically set a value for the special variable $? that indicates the success or failure of a command execution called exit status.

• Successful:0
• Abnormal exit: 1 (or a number other than 0 depending on the command or error type)

The ifup command is a shell script (as noted in the comment) and calls other scripts sequentially as you follow the action, but the exit status seems to have been set to the same value as described above, so you should use this value.