centos learning: shell to start the batch? 777? Rwx how control

[root@localhost shell]# ls -l
total 16
-rw-r--r--. 1 root root    5 Jun 22 06:04 aaa
-rwxr-xr-x. 1 root root 6464 Jun 22 06:01 test
-rw-r--r--. 1 root root   68 Jun 22 06:00 test.c

• On behalf of ordinary files
  d for directory

A total of ten after nine representatives of authority

w x r Read Write executed
421

777

File owner fully controllable
same group of users fully controllable
other users fully controllable

chmod u + x aaa give yourself execute permissions
chmod g + x aaa crew permission to
chmod o + x aaa permissions to other persons

Write echo in the file "123" may be executed as an execution file if the system determines that the scribble not an executable file

[root@localhost shell]# ./aaa
./aaa: line 1: sd:x: command not found