echo $?总是返回0

ha_

1. suntest# ls
   
2. ok1  ok2
   
3. suntest# ls ok3
   
4. /usr/local/bin/ls: ok3: No such file or directory
   
5. suntest# echo $?
   
6. 0
   
7. suntest# cp ok2 ok3
   
8. suntest# echo addline >> ok3
   
9. suntest# diff ok2 ok3
   
10. 2a3
    
11. > addline
    
12. suntest# echo $?
    
13. 0
    
14. suntest# ll
    
15. bash: ll: command not found
    
16. suntest# echo $?
    
17. 0
    
18. suntest#
    

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1. 
   
2. suntest# /bin/bash
   
3. bash-2.05# ll
   
4. bash: ll: command not found
   
5. bash-2.05# echo $?
   
6. 127
   
7. bash-2.05# ls /opp
   
8. /opp: No such file or directory
   
9. bash-2.05# echo $?
   
10. 2
    
11. bash-2.05# pwd
    
12. /export/home/info/test
    
13. bash-2.05# echo $?
    
14. 0
    
15. bash-2.05# diff ok2 ok3
    
16. 2a3
    
17. > addline
    
18. bash-2.05# echo $?
    
19. 1
    
20. bash-2.05# cp ok3 ok4;diff ok3 ok4 > /dev/null 2>&1; echo $?
    
21. 0
    
22. bash-2.05# exit
    
23. exit
    
24. suntest#
    

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是环境设置的问题吗?