linux file 命令简介：
该命令用来识别文件类型，也可用来辨别一些文件的编码格式。它是通过查看文件的头部信息来获取文件类型，而不是像Windows通过扩展名来确定文件类型的。
更多介绍可以查看这篇文章：//www.jb51.net/LINUXjishu/388984.html
file 官方解释：Determine type of FILEs. 判定文件的类型。
小知识：在UNIX/Linux系统中，文件类型并不是由扩展名决定的（Windows是的）。
开篇例子:
1. $file file.txt
输出：file.txt: ASCII English text
注：file.txt是我用file –help > file.txt生成的帮助文档
查看—help
Usage: file [OPTION...] [FILE...]
Determine type of FILEs.
--help display this help and exit
-v, --version output version information and exit
-m, --magic-file LIST use LIST as a colon-separated list of magic
number files
-z, --uncompress try to look inside compressed files
-b, --brief do not prepend filenames to output lines
-c, --checking-printout print the parsed form of the magic file, use in
conjunction with -m to debug a new magic file before installing it
-e, --exclude TEST exclude TEST from the list of test to be performed for file. Valid tests are: ascii, apptype, compress, elf, soft, tar, tokens, troff
-f, --files-from FILE read the filenames to be examined from FILE
-F, --separator STRING use string as separator instead of `:'
-i, --mime output MIME type strings (--mime-type and
--mime-encoding)
--apple output the Apple CREATOR/TYPE
--mime-type output the MIME type
--mime-encoding output the MIME encoding
-k, --keep-going don't stop at the first match
-l, --list list magic strength
-L, --dereference follow symlinks (default)
-h, --no-dereference don't follow symlinks
-n, --no-buffer do not buffer output
-N, --no-pad do not pad output
-0, --print0 terminate filenames with ASCII NUL
-p, --preserve-date preserve access times on files
-r, --raw don't translate unprintable chars to ooo
-s, --special-files treat special (block/char devices) files as ordinary ones
-C, --compile compile file specified by -m
-d, --debug print debugging messages
解读：
1. -z
查看压缩文件内的信息
2. -b, -e, -i, –r
-b 去掉输出行的前缀命名
-e 从测试列表到被执行文件排除测试。有效的测试包括：ascii, apptype, compress, elf, soft, tar,
-i 打印MIME
-R 不转译无法打印的字符为ooo
