1. ### BEGIN: Piples ###
    3. ps aux | grep nethack | wc -l
    5. ### BEGIN: xargs ###
    7. find / -name '*.txt' -size +10K -user ronnie -not -perm /o=r -exec chmod o+r {} \; # CMD1
    8. find / -name '*.txt' -size +10K -user ronnie -not -perm /o=r | xargs chmod o+r           # CMD2
    10. # CMD2 比 CMD1 更简洁，并且速度更快，因为所有匹配的文件一次性的传给了 chmod。
    11. # xargs -l # each line
    12. #                -p # prompt you before executing each command.
    13. ### END:   xargs ###
    15. ### END: Piples ###
    17. ### BEGIN: Boolean Operators ###
    18. cmd1 && cmd2 # cmd1 执行成功（exit status = 0）之后才会执行 cmd2
    19. cmd1 || cmd2 # cmd1 执行失败（exit status = 1）之后才会执行 cmd2
    20. ### END:   Boolean Operators ###
    22. ### BEGIN: ; ###
    23. cmd1 ; cmd2 ; cmd3 # 顺序执行 cmd1-3，无论成功与否 
    24. ### END:   ; ###
    26. ### BEGIN: Process Substitution ###
    27. cat <(ls -al) # 效果同 ls -al | cat
    28. diff <(ls dir1) <(ls dir2) # 效果同下
    29. # ls dir1 > file1.txt
    30. # ls dir2 > file2.txt
    31. # diff file1.txt file2.txt
    32. ### END:   Process Substitution ###