du

Estimate file space usage, reports the amount of disk space used by the specified files and for each subdirectory.（计算文件或目录所占用的硬盘空间）

SYNTAX
      du [options]... [file]...

With no arguments, `du' reports the disk space for the current directory. Normally the disk space is printed in units of 1024 bytes, but this can be overridden

frequently used options

`-a' (utility)
`--all'
     Show counts for all files, not just directories.

`-c' (same as -x)
`--total'
     Print a grand total of all arguments after all arguments have been
     processed. This can be used to find out the total disk usage of a
     given set of files or directories.(作用与-x相同)

`-D'
`--dereference-args'
     Dereference symbolic links that are command line arguments. Does
     not affect other symbolic links. This is helpful for finding out
     the disk usage of directories, such as `/usr/tmp', which are often
     symbolic links.

`-h' (utility)
`--human-readable'
     Append a size letter such as `M' for megabytes to each size.
     Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes.
     Use the `-H' or `--si' option if you prefer powers of 1000.

`-H'
`--si'
     Append a size letter such as `M' for megabytes to each size. (SI
     is the International System of Units, which defines these letters
     as prefixes.) Powers of 1000 are used, not 1024; `M' stands for
     1,000,000 bytes. Use the `-h' or `--human-readable' option if you
     prefer powers of 1024.(假如你想用单位为1000，而不是1024来计算目录或文件的大小时，就用-H)

`-l'
`--count-links'
     Count the size of all files, even if they have appeared already
     (as a hard link).(相当于-a)

`-L'(没有多大的用处)
`--dereference'
     Dereference symbolic links (show the disk space used by the file
     or directory that the link points to instead of the space used by
     the link).

`--max-depth=DEPTH' (utility实用)
     Show the total for each directory (and file if -all) that is at
     most MAX_DEPTH levels down from the root of the hierarchy. The
     root is at level 0, so `du --max-depth=0' is equivalent to `du -s'.

`-s' (utility)
`--summarize'
     Display only a total for each argument.

`-S'
`--separate-dirs'
     Report the size of each directory separately, not including the
     sizes of subdirectories.

`-x'
`--one-file-system'
     Skip directories that are on different filesystems from the one
     that the argument being processed is on.（计算所给目录及其所有的子目录的大小）

`--exclude=PAT'
     When recursing, skip subdirectories or files matching PAT. For
     example, `du --exclude='*.o'' excludes files whose names end in
     `.o'.

`-X FILE'
`--exclude-from=FILE'
     Like `--exclude', except take the patterns to exclude from FILE,
     one per line. If FILE is `-', take the patterns from standard
     input.
     
 example:
 计算当前目录及其所有子目录的大小
 $du -xh(or -ch)
 计算某个目录的总的大小
 #du -sh /usr
 2.7G /usr
 假如目录/tmp1下有5个文件，总的大小为200K，还有一个子目录tmp2，总的大小为300K，现在只想计算目录/tmp1的大小，而不包括子目录tmp2的大小，可用-S
 $du -Sh /tmp1
 300k /tmp1/tmp2
 204K /tmp1
 你想计算当前目录下的最大深度为2的所有目录的大小
 $du -xh --max-depth=2
 你想计算当前目录下的最大深度为5的所有目录的大小,但不包括那些以.doc结尾的文件的大小
 $du -xh --max-depth=2 --exclude='*.doc'