1、基本的正则表达式
- 显示/proc/meminfo文件中以大小s开头的行(要求：使用两种方法)
[root@centos7 app]#cat /proc/meminfo|grep "^[sS]"
SwapCached: 28 kB
SwapTotal: 2097148 kB
SwapFree: 2097060 kB
Shmem: 7796 kB
Slab: 108060 kB
SReclaimable: 50880 kB
SUnreclaim: 57180 kB
[root@centos7 app]#cat /proc/meminfo|grep -i "^s"
SwapCached: 28 kB
SwapTotal: 2097148 kB
SwapFree: 2097060 kB
Shmem: 7796 kB
Slab: 108060 kB
SReclaimable: 50880 kB
SUnreclaim: 57180 kB
- 显示/etc/passwd文件中不以/bin/bash结尾的行
cat /etc/passwd |grep -v "/bin/bash$"
[root@centos7 app]#cat /etc/passwd |grep "^rpc\>"|cut -d: -f7
/sbin/nologin
[root@centos7 app]#cat /etc/passwd |grep -w "^rpc"|cut -d: -f7
/sbin/nologin
grep -o "\<[0-9]\{2,3\}\>" /etc/passwd
- 显示CentOS7的/etc/grub2.cfg文件中，至少以一个空白字符开头的且后面存非空白字符的行
cat /etc/grub2.cfg |grep "^[[:space:]]\+[^[:space:]]"
- 找出“netstat -tan”命令的结果中以‘LISTEN’后跟任意多个空白字符结尾的行
netstat -tan |grep "LISTEN[[:space:]]*$"
- 显示CentOS7和centos6上所有系统用户的用户名和UID
cat /etc/passwd |cut -d: -f1,3|grep "\<[0-9]\{1,3\}\>"
cat /etc/passwd |cut -d: -f1,3|grep "\<\([0-9]\{1,2\}\|[1-4][0-9]\{2\}\)\>"
- 添加用户bash、testbash、basher、sh、nologin(其shell为/sbin/nologin),找出/etc/passwd用户名同shell名的行
grep "^\([[:alnum:]_]\+\>\).*\<\1$" /etc/passwd
- 利用df和grep，取出磁盘各分区利用率，并从大到小排序
[root@centos6 app]#df |grep "^/dev/sd"|tr -s " " "%"|cut -d% -f5|sort -nr
10
4
1
2、扩展的正则表达式
- 显示三个用户root、mage、wang的UID和默认shell
[root@centos6 app]#cat /etc/passwd |egrep "^(root|zhang|tom)\>"|cut -d: -f1,3,7
root:0:/bin/bash
zhang:500:/bin/bash
tom:504:/bin/bash
- 找出/etc/rc.d/init.d/functions文件中行首为某单词(包括下划线)后面跟一个小括号的行
egrep "^[[:alpha:]_]+\(\)" /etc/rc.d/init.d/functions
- 使用egrep取出/etc/rc.d/init.d/functions中其基名
[root@centos6 app]#echo /etc/rc.d/init.d/functions |egrep -o "[^/]+/?$"
functions
[root@centos6 app]#echo /etc/rc.d/init.d/functions/ |egrep -o "[^/]+/?$"
functions/
[root@centos6 app]#echo /etc/rc.d/init.d/functions/ |egrep -o "^/.*/\<"
/etc/rc.d/init.d/
[root@centos6 app]#echo /etc/rc.d/init.d/functions |egrep -o "^/.*/\<"
/etc/rc.d/init.d/
- 统计last命令中以root登录的每个主机IP地址登录次数
[root@centos6 app]#last |egrep "^root\>"|egrep -o "(\<[0-9]{1,3}\.){3}\<[0-9]{1,3}\>"|sort|uniq -c
59 192.168.25.1
- 利用扩展正则表达式分别表示0-9、10-99、100-199、200-249、250-255
echo {0..255}|egrep -o "\<\[0-9]>"
echo {0..255}|egrep -o "\<[1-9][0-9]\>"
echo {0..255}|egrep -o "\<1[0-9]{2}\>"
echo {0..255}|egrep -o "\<2[0-4][0-9]\>"
echo {0..255}|egrep -o "\<25[0-5]\>"
ifconfig |egrep -o "\<(([0-9]{1,2}|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]{1,2}|1[0-9]{2}|2[0-4][0-9]|25[0-5])\>"
- 将此字符串：welcome to magedu linux 中的每个字符去重并排序，重复次数多的排到前面
echo "welcome to magedu linux" |egrep -o [[:alpha:]] |sort|uniq -c
- 将/misc/cd/Packages 文件中以.rpm结尾的文件，cpu架构取出来，并统计每种架构出现的次数
[root@centos6 Packages]#ls *.rpm |egrep -o "[^.]*\.rpm$"|cut -d "." -f1|sort|uniq -c
4 i686
925 noarch
2311 x86_64
[root@centos6 Packages]#ls *.rpm |rev|cut -d "." -f2|rev|sort|uniq -c
4 i686
925 noarch
2311 x86_64
