英文全称：
    功能：查看文件类型

    1. #查看文本文件的类型
    2. [root@kedacom test]# file teacher.txt 
    3. teacher.txt: ASCII text
    5. #查看命令文件的类型
    6. [root@kedacom test]# which cat
    7. /usr/bin/cat
    8. [root@kedacom test]# file /usr/bin/cat
    9. /usr/bin/cat: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=fefad10b7ae154c0df1acbdbb8334c77081a77ee, stripped