127 Return code from $?

Value 127 is returned by /bin/sh when the given command is not found within your PATH system variable and it is not a built-in shell command. In other words, the system doesn't understand your command, because it doesn't know where to find the binary you're trying to call.

Generally it means:

127 - command not found

but it can also mean that the command is found,
but a library that is required by the command is NOT found.

127 - command not found

example: $caat The error message will

bash:

caat: command not found

now you check using echo $?