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  • Linux CentOS7 VMware正则介绍、grep工具、egrep表达式

    一、正则介绍

    正则是学习shell脚本的必学的内容,正则学的好坏直接影响到shell编程能力。

    正则表达式:使用单个字符串来描述或匹配一系列符合某个句法规则的字符串。通常用来检索和替换那些符合某个模式的文本内容。正则表达式贯穿到整个运维日常,无论是查找某个文件,还是查询某个日志文件并分析其内容均用到。

    正则表达式是一种思想,一种表示方法。常用的工具grep、sed、awk三剑客。

    二、grep上

    grep全称是Global Regular Expression Print,表示全局正则表达式版本,它的使用权限是所有用户

    命令格式:grep -cinvABC '关键字' 文件名

    -c:显示出含关键字有多少行,会显示一个数字

    -i:不区分大小写

    -n:显示出含关键字的行及行号,前面会标出行号

    -v:取反,显示出不含关键字的行

    -r:遍历所有子目录

    -An:n为数字,表示显示出含关键字的行及面n行

    -Bn;n为数字,表示显示出含关键字要求的行及面n行

    -Cn;n为数字,表示显示出含关键字要求的行,及上下n行

    ·例子:

    [root@davery ~]# mkdir grep
    [root@davery ~]# cd grep/
    [root@davery grep]# cp /etc/passwd .
    [root@davery grep]# ls
    passwd
    [root@davery grep]#

    [root@davery grep]# pwd
    /root/grep
    [root@davery grep]# ls
    passwd

    [root@davery grep]# grep 'nologin' passwd    显示出passwd下面含有nologin所有行
    bin:x:1:1:bin:/bin:/sbin/nologin
    daemon:x:2:2:daemon:/sbin:/sbin/nologin
    adm:x:3:4:adm:/var/adm:/sbin/nologin
    lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    operator:x:11:0:operator:/root:/sbin/nologin
    games:x:12:100:games:/usr/games:/sbin/nologin
    ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    nobody:x:99:99:Nobody:/:/sbin/nologin
    systemd-network:x:192:192:systemd Network Management:/:/sbin/nologin
    dbus:x:81:81:System message bus:/:/sbin/nologin
    polkitd:x:999:997:User for polkitd:/:/sbin/nologin
    postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
    chrony:x:998:996::/var/lib/chrony:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# which grep
    alias grep='grep --color=auto'          在Centos7中关键字会有颜色
    /usr/bin/grep
    [root@davery grep]#

    [root@davery grep]# grep -c 'nologin' passwd        显示出passwd文件名下含有nologin关键字的行共有15行
    15

    [root@davery grep]# grep -n 'nologin' passwd        显示出passwd文件名下显示含有nologin关键字的行及行号
    2:bin:x:1:1:bin:/bin:/sbin/nologin
    3:daemon:x:2:2:daemon:/sbin:/sbin/nologin
    4:adm:x:3:4:adm:/var/adm:/sbin/nologin
    5:lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    9:mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    10:operator:x:11:0:operator:/root:/sbin/nologin
    11:games:x:12:100:games:/usr/games:/sbin/nologin
    12:ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    13:nobody:x:99:99:Nobody:/:/sbin/nologin
    14:systemd-network:x:192:192:systemd Network Management:/:/sbin/nologin
    15:dbus:x:81:81:System message bus:/:/sbin/nologin
    16:polkitd:x:999:997:User for polkitd:/:/sbin/nologin
    17:postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    18:sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
    19:chrony:x:998:996::/var/lib/chrony:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# grep -i 'nologin' passwd   显示出passwd文件名下含有关键字nologin的行,不区分大小写
    bin:x:1:1:bin:/bin:/sbin/NOLOGIN
    daemon:x:2:2:daemon:/sbin:/sbin/nologin
    adm:x:3:4:adm:/var/adm:/sbin/nologin
    lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    operator:x:11:0:operator:/root:/sbin/nologin
    games:x:12:100:games:/usr/games:/sbin/nologin
    ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    nobody:x:99:99:Nobody:/:/sbin/nologin
    systemd-network:x:192:192:systemd Network Management:/:/sbin/nologin
    dbus:x:81:81:System message bus:/:/sbin/nologin
    polkitd:x:999:997:User for polkitd:/:/sbin/nologin
    postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
    chrony:x:998:996::/var/lib/chrony:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# grep -ni 'nologin' passwd 显示出passwd文件名下含有关键字nologin的所在行,不区分大小写
    2:bin:x:1:1:bin:/bin:/sbin/NOLOGIN
    3:daemon:x:2:2:daemon:/sbin:/sbin/nologin
    4:adm:x:3:4:adm:/var/adm:/sbin/nologin
    5:lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    9:mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    10:operator:x:11:0:operator:/root:/sbin/nologin
    11:games:x:12:100:games:/usr/games:/sbin/nologin
    12:ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    13:nobody:x:99:99:Nobody:/:/sbin/nologin
    14:systemd-network:x:192:192:systemd Network Management:/:/sbin/nologin
    15:dbus:x:81:81:System message bus:/:/sbin/nologin
    16:polkitd:x:999:997:User for polkitd:/:/sbin/nologin
    17:postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    18:sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
    19:chrony:x:998:996::/var/lib/chrony:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# grep -nv 'nologin' passwd   取反
    1:root:x:0:0:root:/root:/bin/bash
    2:bin:x:1:1:bin:/bin:/sbin/NOLOGIN     此时还会区分大小写,大写的不是关键字
    6:sync:x:5:0:sync:/sbin:/bin/sync
    7:shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
    8:halt:x:7:0:halt:/sbin:/sbin/halt
    20:davery:x:1000:1003::/home/davery:/bin/bash
    21:uaer1:x:1001:1004::/home/uaer1:/bin/bash
    22:user2:x:1002:1005::/home/user2:/bin/bash
    23:user3:x:1006:1006::/home/user3:/bin/bash
    24:user4:x:1007:898::/home/user4:/bin/bash
    25:user6:x:1008:898::/home/user6:/bin/bash
    [root@davery grep]#

    [root@davery grep]# grep -niv 'nologin' passwd  取反,显示行号,不区分大小写
    1:root:x:0:0:root:/root:/bin/bash
    6:sync:x:5:0:sync:/sbin:/bin/sync
    7:shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
    8:halt:x:7:0:halt:/sbin:/sbin/halt
    20:davery:x:1000:1003::/home/davery:/bin/bash
    21:uaer1:x:1001:1004::/home/uaer1:/bin/bash
    22:user2:x:1002:1005::/home/user2:/bin/bash
    23:user3:x:1006:1006::/home/user3:/bin/bash
    24:user4:x:1007:898::/home/user4:/bin/bash
    25:user6:x:1008:898::/home/user6:/bin/bash
    [root@davery grep]#

    [root@davery grep]# grep -inv 'nologin' passwd   inv不分先后
    1:root:x:0:0:root:/root:/bin/bash
    6:sync:x:5:0:sync:/sbin:/bin/sync
    7:shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
    8:halt:x:7:0:halt:/sbin:/sbin/halt
    20:davery:x:1000:1003::/home/davery:/bin/bash
    21:uaer1:x:1001:1004::/home/uaer1:/bin/bash
    22:user2:x:1002:1005::/home/user2:/bin/bash
    23:user3:x:1006:1006::/home/user3:/bin/bash
    24:user4:x:1007:898::/home/user4:/bin/bash
    25:user6:x:1008:898::/home/user6:/bin/bash
    [root@davery grep]#

    [root@davery grep]# grep 'root' /etc/
    grep: /etc/: 是一个目录
    [root@davery grep]#

    [root@davery grep]# grep -r 'root' /etc/ > /tmp/grep.log  针对目录来显示
    [root@davery grep]# grep passwd /tmp/grep.log
    /etc/passwd:root:x:0:0:root:/root:/bin/bash
    /etc/passwd:operator:x:11:0:operator:/root:/sbin/nologin
    /etc/passwd-:root:x:0:0:root:/root:/bin/bash
    /etc/passwd-:operator:x:11:0:operator:/root:/sbin/nologin
    /etc/postfix/main.cf:# the system passwd file in the chroot jail is just not practical.
    [root@davery grep]#

    [root@davery grep]# grep -A2 'root' passwd  在passwd文件名下显示出含有root的行及下面2行
    root:x:0:0:root:/root:/bin/bash
    bin:x:1:1:bin:/bin:/sbin/NOLOGIN
    daemon:x:2:2:daemon:/sbin:/sbin/nologin
    --
    operator:x:11:0:operator:/root:/sbin/nologin
    games:x:12:100:games:/usr/games:/sbin/nologin
    ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# grep -nA2 'root' passwd  在passwd文件名下显示出含有root的行及下面2行,及所在行号
    1:root:x:0:0:root:/root:/bin/bash
    2-bin:x:1:1:bin:/bin:/sbin/NOLOGIN
    3-daemon:x:2:2:daemon:/sbin:/sbin/nologin
    --
    10:operator:x:11:0:operator:/root:/sbin/nologin
    11-games:x:12:100:games:/usr/games:/sbin/nologin
    12-ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# grep -nB2 'root' passwd 在passwd文件名下显示出含有root的行及上面2行,及所在行号
    1:root:x:0:0:root:/root:/bin/bash
    --
    8-halt:x:7:0:halt:/sbin:/sbin/halt
    9-mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    10:operator:x:11:0:operator:/root:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# grep -nC2 'root' passwd 在passwd文件名下显示出含有root的行及上、下面各2行,及所在行号
    1:root:x:0:0:root:/root:/bin/bash
    2-bin:x:1:1:bin:/bin:/sbin/NOLOGIN
    3-daemon:x:2:2:daemon:/sbin:/sbin/nologin
    --
    8-halt:x:7:0:halt:/sbin:/sbin/halt
    9-mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    10:operator:x:11:0:operator:/root:/sbin/nologin
    11-games:x:12:100:games:/usr/games:/sbin/nologin
    12-ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    [root@davery grep]#

    三、grep中正则表达式

    [root@davery grep]# grep '[0-9]' /etc/inittab 显示出/etc/inittab下所有带数字的行,若行没有数字则显示不出来

    # multi-user.target: analogous to runlevel 3
    # graphical.target: analogous to runlevel 5
    [root@davery grep]#

    [root@davery grep]# grep -v '[0-9]' /etc/inittab  显示出/etc/inittab文件名下不含数字的行
    # inittab is no longer used when using systemd.
    #
    # ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
    #
    # Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target
    #
    # systemd uses 'targets' instead of runlevels. By default, there are two main targets:
    #
    #
    # To view current default target, run:
    # systemctl get-default
    #
    # To set a default target, run:
    # systemctl set-default TARGET.target
    #
    [root@davery grep]#

    [root@davery grep]# grep -n '^#' /etc/inittab  显示出以#开头的行,并显示行号
    1:# inittab is no longer used when using systemd.
    2:#
    3:# ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
    4:#
    5:# Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target
    6:#
    7:# systemd uses 'targets' instead of runlevels. By default, there are two main targets:
    8:#
    9:# multi-user.target: analogous to runlevel 3
    10:# graphical.target: analogous to runlevel 5
    11:#
    12:# To view current default target, run:
    13:# systemctl get-default
    14:#
    15:# To set a default target, run:
    16:# systemctl set-default TARGET.target
    17:#
    [root@davery grep]#

    [^]  匹配非方括号里面的内容。就是:只要不是方括号里面的内容都显示出来。

    ^[^] 匹配非方括号里面的内容开头的所有字符,只要不是方括号里面的内容所开头的,都显示出来。

    [root@davery grep]# grep '[^0-9]' /etc/inittab  不显示纯数字的行

    # inittab is no longer used when using systemd.

    #
    # ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
    #
    # Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target
    #
    # systemd uses 'targets' instead of runlevels. By default, there are two main targets:
    #
    # multi-user.target: analogous to runlevel 3
    # graphical.target: analogous to runlevel 5
    #
    # To view current default target, run:
    # systemctl get-default
    #
    # To set a default target, run:
    # systemctl set-default TARGET.target
    #

    [root@davery grep]# grep '^[^0-9]' /etc/inittab    显示不以数字开头的行
    # inittab is no longer used when using systemd.
    #
    # ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
    #
    # Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target
    #
    # systemd uses 'targets' instead of runlevels. By default, there are two main targets:
    #
    # multi-user.target: analogous to runlevel 3
    # graphical.target: analogous to runlevel 5
    #
    # To view current default target, run:
    # systemctl get-default
    #
    # To set a default target, run:
    # systemctl set-default TARGET.target
    #
    [root@davery grep]#

    显示特殊字符相关

    root@davery grep]#
    [root@davery grep]# grep 'r.o' passwd               .代表r与o之间任意一个字符,多字符不会标记显示
    root:x:0:0:root:/root:/bin/bash
    operator:x:11:0:operator:/root:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# grep 'ro*o' passwd       *代表任意字符可以为空   
    root:x:0:0:root:/root:/bin/bash
    operator:x:11:0:operator:/root:/sbin/nologin
    chrony:x:998:996::/var/lib/chrony:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# grep 'ro*t' passwd
    root:x:0:0:root:/root:/bin/bash
    operator:x:11:0:operator:/root:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# grep -n ':[0-9]' passwd  
    1:root:x:0:0:root:/root:/bin/bash
    2:bin:x:1:1:bin:/bin:/sbin/NOLOGIN
    3:daemon:x:2:2:daemon:/sbin:/sbin/nologin
    4:adm:x:3:4:adm:/var/adm:/sbin/nologin
    5:lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    6:sync:x:5:0:sync:/sbin:/bin/sync
    7:shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
    8:halt:x:7:0:halt:/sbin:/sbin/halt
    9:mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    10:operator:x:11:0:operator:/root:/sbin/nologin
    11:games:x:12:100:games:/usr/games:/sbin/nologin
    12:ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    13:nobody:x:99:99:Nobody:/:/sbin/nologin
    14:systemd-network:x:192:192:systemd Network Management:/:/sbin/nologin
    15:dbus:x:81:81:System message bus:/:/sbin/nologin
    16:polkitd:x:999:997:User for polkitd:/:/sbin/nologin
    17:postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    18:sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
    19:chrony:x:998:996::/var/lib/chrony:/sbin/nologin
    20:davery:x:1000:1003::/home/davery:/bin/bash
    21:uaer1:x:1001:1004::/home/uaer1:/bin/bash
    22:user2:x:1002:1005::/home/user2:/bin/bash
    23:user3:x:1006:1006::/home/user3:/bin/bash
    24:user4:x:1007:898::/home/user4:/bin/bash
    25:user6:x:1008:898::/home/user6:/bin/bash
    [root@davery grep]#

    [root@davery grep]# grep -n '8:*' passwd
    9:mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    15:dbus:x:81:81:System message bus:/:/sbin/nologin
    17:postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    19:chrony:x:998:996::/var/lib/chrony:/sbin/nologin
    24:user4:x:1007:898::/home/user4:/bin/bash
    25:user6:x:1008:898::/home/user6:/bin/bash
    [root@davery grep]#

    [root@davery grep]# grep -n '8:*[8-9]' passwd
    17:postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    19:chrony:x:998:996::/var/lib/chrony:/sbin/nologin
    24:user4:x:1007:898::/home/user4:/bin/bash
    25:user6:x:1008:898::/home/user6:/bin/bash
    [root@davery grep]#

    [root@davery grep]# grep 'user6.*bash' passwd     .*表示零个或多个任意字符
    user6:x:1008:898::/home/user6:/bin/bash
    [root@davery grep]#

    [root@davery grep]# grep 'o\{2\}' passwd     加入转义符\,o\{2\ }表示括号前边o出现2次重复
    root:x:0:0:root:/root:/bin/bash 
    lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    operator:x:11:0:operator:/root:/sbin/nologin
    postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# grep 'o\{0,3\}' passwd        0,3范围匹配,o\{0,3\}表示括号前边出现0次1次2次3次重复
    root:x:0:0:root:/root:/bin/bash
    bin:x:1:1:bin:/bin:/sbin/NOLOGIN
    daemon:x:2:2:daemon:/sbin:/sbin/nologin
    adm:x:3:4:adm:/var/adm:/sbin/nologin
    lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    sync:x:5:0:sync:/sbin:/bin/sync
    shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
    halt:x:7:0:halt:/sbin:/sbin/halt
    mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    operator:x:11:0:operator:/root:/sbin/nologin
    games:x:12:100:games:/usr/games:/sbin/nologin
    ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    nobody:x:99:99:Nobody:/:/sbin/nologin
    systemd-network:x:192:192:systemd Network Management:/:/sbin/nologin
    dbus:x:81:81:System message bus:/:/sbin/nologin
    polkitd:x:999:997:User for polkitd:/:/sbin/nologin
    postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
    chrony:x:998:996::/var/lib/chrony:/sbin/nologin
    davery:x:1000:1003::/home/davery:/bin/bash
    uaer1:x:1001:1004::/home/uaer1:/bin/bash
    user2:x:1002:1005::/home/user2:/bin/bash
    user3:x:1006:1006::/home/user3:/bin/bash
    user4:x:1007:898::/home/user4:/bin/bash
    user6:x:1008:898::/home/user6:/bin/bash
    [root@davery grep]#

    五、egrep表达式

    [root@davery grep]# grep -E 'o{2}' passwd  等同于egrep 'o{2}' passwd

    root:x:0:0:root:/root:/bin/bash
    lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    operator:x:11:0:operator:/root:/sbin/nologin
    postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# egrep 'o+' passwd  表示o出现1次,等同于grep 'o\{1\}' passwd

    root:x:0:0:root:/root:/bin/bash
    daemon:x:2:2:daemon:/sbin:/sbin/nologin
    adm:x:3:4:adm:/var/adm:/sbin/nologin
    lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
    mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    operator:x:11:0:operator:/root:/sbin/nologin
    games:x:12:100:games:/usr/games:/sbin/nologin
    ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    nobody:x:99:99:Nobody:/:/sbin/nologin
    systemd-network:x:192:192:systemd Network Management:/:/sbin/nologin
    dbus:x:81:81:System message bus:/:/sbin/nologin
    polkitd:x:999:997:User for polkitd:/:/sbin/nologin
    postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
    chrony:x:998:996::/var/lib/chrony:/sbin/nologin
    davery:x:1000:1003::/home/davery:/bin/bash
    uaer1:x:1001:1004::/home/uaer1:/bin/bash
    user2:x:1002:1005::/home/user2:/bin/bash
    user3:x:1006:1006::/home/user3:/bin/bash
    user4:x:1007:898::/home/user4:/bin/bash
    user6:x:1008:898::/home/user6:/bin/bash
    [root@davery grep]# egrep 'oo+' passwd  等同于egrep 'o{2}' passwd
    root:x:0:0:root:/root:/bin/bash
    lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    operator:x:11:0:operator:/root:/sbin/nologin
    postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    [root@davery grep]#

    [root@davery grep]# egrep 'o?t' passwd 表示o重复1次,后边跟t
    root:x:0:0:root:/root:/bin/bash
    shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
    halt:x:7:0:halt:/sbin:/sbin/halt
    operator:x:11:0:operator:/root:/sbin/nologin
    ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
    systemd-network:x:192:192:systemd Network Management:/:/sbin/nologin
    dbus:x:81:81:System message bus:/:/sbin/nologin
    polkitd:x:999:997:User for polkitd:/:/sbin/nologin
    postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
    [root@davery grep]# egrep 'oo?t' passwd 表示o重复2次,后边跟t
    root:x:0:0:root:/root:/bin/bash
    operator:x:11:0:operator:/root:/sbin/nologin
    [root@davery grep]#

     [root@davery grep]# egrep 'mail|oo' passwd   使用管道符| , 显示出mail或者oo字符串

    root:x:0:0:root:/root:/bin/bash
    lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
    mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
    operator:x:11:0:operator:/root:/sbin/nologin
    postfix:x:89:89::/var/spool/postfix:/sbin/nologin
    [root@davery grep]#

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  • 原文地址:https://www.cnblogs.com/davery/p/8729849.html
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