linux下我们经常要查看目录的组织结构，tree命令以树形结构显示文件目录。
直接使用tree dir显示目录下所有文件和文件夹：
$ tree go
go
├── build.sh
├── compile-run.sh
├── main
└── main.go
tree -d选项只查看目录下文件夹：
$ tree -d cmake
cmake
├── cmake_exe
│ └── CMakeFiles
│ ├── 3.5.1
│ │ ├── CompilerIdC
│ │ └── CompilerIdCXX
│ ├── CMakeTmp
│ └── main.dir
├── cmake_lib
│ ├── bin
│ ├── CMakeFiles
│ │ ├── 3.5.1
│ │ │ ├── CompilerIdC
│ │ │ └── CompilerIdCXX
│ │ └── CMakeTmp
│ ├── lib
│ │ └── CMakeFiles
│ │ └── libhello.dir
│ └── src
│ └── CMakeFiles
│ └── hello.dir
└── cmake_so
tree -L leve查看目录树深度：
$ tree -d -L 2 shell
shell
├── autoupdate
│ └── tools
└── expect-dir
├── bin
├── expect5.45
├── expect-tool
└── tcl8.4.11
7 directories
在shell终端输入tree --help查看所有选项：
$ tree --help
usage: tree [-acdfghilnpqrstuvxACDFJQNSUX] [-H baseHREF] [-T title ]
[-L level [-R]] [-P pattern] [-I pattern] [-o filename] [--version]
[--help] [--inodes] [--device] [--noreport] [--nolinks] [--dirsfirst]
[--charset charset] [--filelimit[=]#] [--si] [--timefmt[=]<f>]
[--sort[=]<name>] [--matchdirs] [--ignore-case] [--] [<directory list>]
------- Listing options -------
-a All files are listed.
-d List directories only.
-l Follow symbolic links like directories.
-f Print the full path prefix for each file.
-x Stay on current filesystem only.
-L level Descend only level directories deep.
-R Rerun tree when max dir level reached.
-P pattern List only those files that match the pattern given.
-I pattern Do not list files that match the given pattern.
--ignore-case Ignore case when pattern matching.
--matchdirs Include directory names in -P pattern matching.
--noreport Turn off file/directory count at end of tree listing.
--charset X Use charset X for terminal/HTML and indentation line output.
--filelimit # Do not descend dirs with more than # files in them.
--timefmt <f> Print and format time according to the format <f>.
-o filename Output to file instead of stdout.
-------- File options ---------
-q Print non-printable characters as '?'.
-N Print non-printable characters as is.
-Q Quote filenames with double quotes.
-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.
--si Like -h, but use in SI units (powers of 1000).
-D Print the date of last modification or (-c) status change.
-F Appends '/', '=', '*', '@', '|' or '>' as per ls -F.
--inodes Print inode number of each file.
--device Print device ID number to which each file belongs.
------- Sorting options -------
-v Sort files alphanumerically by version.
-t Sort files by last modification time.
-c Sort files by last status change time.
-U Leave files unsorted.
-r Reverse the order of the sort.
--dirsfirst List directories before files (-U disables).
--sort X Select sort: name,version,size,mtime,ctime.
------- Graphics options ------
-i Don't print indentation lines.
-A Print ANSI lines graphic indentation lines.
-S Print with CP437 (console) graphics indentation lines.
-n Turn colorization off always (-C overrides).
-C Turn colorization on always.
------- XML/HTML/JSON options -------
-X Prints out an XML representation of the tree.
-J Prints out an JSON representation of the tree.
-H baseHREF Prints out HTML format with baseHREF as top directory.
-T string Replace the default HTML title and H1 header with string.
--nolinks Turn off hyperlinks in HTML output.
---- Miscellaneous options ----
--version Print version and exit.
--help Print usage and this help message and exit.
-- Options processing terminator.
