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cd <directory>

　　Short for "change directory".

　　The shorthand name for the current directory is  .

　　The shorthand name for the parent directory is ..

pwd

　　present working directory

ls

　　list the contents of the present directory

mkdir <directory>　　//<directory> is the represent for the name of the directory

　　Short for "make directory",this command will create a new subdirectory called <directory> located in the current directory

cp <source> <destination>　　// 僅複製單個檔案，不能複製資料夾

　　Short for "copy",this command will allow you to create a duplicate of the file you specify as <source>,whichi it will save in <destination>

　　eg.　　cp hello.c hi.c  // copy hello.c and rename the copyfile as hi.c in the present directory

　　-r <directory> <destinction>　　//加了引數 -r 表示複製資料夾

　　　　Short for "recursive",copy the directory recursively.copy the <directory> and copy every folder that exists inside of it and every file that

rm <file>　　// 僅刪除單個檔案，不能刪除資料夾

　　Short for "remove",this command will delete<file> after it asks you to confirm (y/n) you want to delete it.

　　-f <file>

　　　　Short for "force",foce rm to do exactly what we're telling it to do.　　

　　　　but use at your own peri!there's no undo.

　　-r <directory>

　　　　to delete entire directories you need to use the -r flag,just as was the case with cp.

　　-rf　　

　　　　combine the -r and -f flags into -rf .Again,careful!There's no undo!

mv　　// 移動檔案

　　Short for "move",this command will allow you to effectively rename a file,moving it from <source> to <destination>.　

　　Rename Source to DEST,or move SOURCE(s)to DIRECTORY.

problem: su command cannot use

　　sudo passwd　　// set root password;and then you can use su command　　

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