ls -l /oldboy/.txt ---匹配以.txt结尾信息进行详细显示
rm -rf /oldboy/ --- 删除oldboy目录中所有信息, 但是默认无法删除隐藏文件
rm -f /oldboy/.old.txt --- 删除以old开头 .txt结尾的所有隐藏文件
find /oldboy -name ".txt"
find /oldboy -name "oldboy"
find /oldboy -name "old.txt"

^ --- 以什么开头的信息

    # ll /etc/|grep "^d"
    drwxr-xr-x.  3 root root      101 Jul  3 20:25 abrt
    drwxr-xr-x.  2 root root      252 Jul 17 18:13 alternatives
    drwxr-x---.  3 root root       43 Jul  3 20:26 audisp
    $   --- 以什么结尾的信息
    # grep 'd$' /etc/selinux/config
    SELINUX=disabled
    SELINUXTYPE=targeted
      说明: 如果结尾有空格信息, 过滤是会出现异常
          利用底行模式 :set list 可以查看结尾空格信息
          利用命令查看 cat -A /etc/selinux/config
    问题: 将以点结尾的信息过滤出来:
   grep '\.$' /etc/selinux/config
    # This file controls the state of SELinux on the system.
    #     enforcing - SELinux security policy is enforced.
    #     permissive - SELinux prints warnings insteadof enforcing.
    #     disabled- No SELinux policy is loaded.
    #     minimum - Modification of targetedpolicy. Only selectedprocesses are protected.
    #     mls - Multi Level Security protection.

过滤出所有小写字母:

    grep "[a-z]" oldboy.txt     --- 过滤小写字母
    grep "[A-Z]" oldboy.txt     --- 过滤大写字母
    grep "[a-zA-Z]" oldboy.txt  --- 过滤所有字母
    grep "[a-Z]" oldboy.txt     --- 过滤所有字母 
    grep -i "[a-z]" oldboy.txt  --- grep忽略大小写进行过滤
    [^] --- 将指定字符信息,进行取反过滤
    [root@oldboyedu oldboy]# grep -v "[a-Z]" oldboy.txt

    [root@oldboyedu oldboy]# grep  "[^a-Z]" oldboy.txt
    I am oldboy teacher!
    I teach linux.
    I like badminton ball ,billiard ball and chinese chess!
    my blog is http://oldboy.blog.51cto.com
    our site is http://www.etiantian.org
    my qq num is 49000448.
    not 4900000448.
    my god ,i am not oldbey,but OLDBOY!

匹配文件中数字0信息

    [root@oldboyedu oldboy]# grep "0*" oldboy.txt 
    I am oldboy teacher!
    I teach linux.
    
    I like badminton ball ,billiard ball and chinese chess!
    my blog is http://oldboy.blog.51cto.com
    our site is http://www.etiantian.org
    my qq num is 49000448.
    
    not 4900000448.
    my god ,i am not oldbey,but OLDBOY!
    [root@oldboyedu oldboy]# grep -o "0*" oldboy.txt 
    000
    00000

.*  --- 匹配文件中所有信息
    [root@oldboyedu oldboy]# grep  ".*" oldboy.txt -o
    I am oldboy teacher!
    I teach linux.
    I like badminton ball ,billiard ball and chinese chess!
    my blog is http://oldboy.blog.51cto.com
    our site is http://www.etiantian.org
    my qq num is 49000448.
    not 4900000448.
    my god ,i am not oldbey,but OLDBOY!