ubuntu下的安装命令：
apt-get install tree
帮助命令：
tree --help
usage: tree [-adfghilnpqrstuvxACDFNS] [-H baseHREF] [-T title ] [-L level [-R]]
[-P pattern] [-I pattern] [-o filename] [--version] [--help] [--inodes]
[--device] [--noreport] [--nolinks] [--dirsfirst] [--charset charset]
[--filelimit #] [<directory list>]
-a All files are listed.
-d List directories only.
-l Follow symbolic links like directories.
-f Print the full path prefix for each file.
-i Don't print indentation lines.
-q Print non-printable characters as '?'.
-N Print non-printable characters as is.
-p Print the protections for each file.
-u Displays file owner or UID number.
-g Displays file group owner or GID number.
-s Print the size in bytes of each file.
-h Print the size in a more human readable way.
-D Print the date of last modification.
-F Appends '/', '=', '*', or '|' as per ls -F.
-v Sort files alphanumerically by version.
-r Sort files in reverse alphanumeric order.
-t Sort files by last modification time.
-x Stay on current filesystem only.
-L level Descend only level directories deep.
-A Print ANSI lines graphic indentation lines.
-S Print with ASCII graphics indentation lines.
-n Turn colorization off always (-C overrides).
-C Turn colorization on always.
-P pattern List only those files that match the pattern given.
-I pattern Do not list files that match the given pattern.
-H baseHREF Prints out HTML format with baseHREF as top directory.
-T string Replace the default HTML title and H1 header with string.
-R Rerun tree when max dir level reached.
-o file Output to file instead of stdout.
--inodes Print inode number of each file.
--device Print device ID number to which each file belongs.
--noreport Turn off file/directory count at end of tree listing.
--nolinks Turn off hyperlinks in HTML output.
--dirsfirst List directories before files.
--charset X Use charset X for HTML and indentation line output.
--filelimit # Do not descend dirs with more than # files in them.
只显示目录：
tree -d
