Linux----正则表达式练习题题解

1、显示/etc/rc.d/rc.sysinit文件中以不区分大小的h开头的行；

[root@openEuler ~]# grep -E "^(H|h)" /etc/passwd
halt:x:7:0:halt:/sbin:/sbin/halt

注：当然也可以使用grep -i来实现，这里我换了一个文件（/etc/passwd）

2、显示/etc/passwd中以sh结尾的行;

[root@openEuler ~]# grep -E "sh$" /etc/passwd
root:x:0:0:Super User:/root:/bin/bash
openeuler:x:1000:1000:openEuler:/home/openeuler:/bin/bash
test02:x:1004:1004::/home/test02:/bin/bash
test03:x:1005:1005::/home/test03:/bin/bash
test04:x:1006:1006::/home/test04:/bin/bash
test05:x:1007:1007::/home/test05:/bin/bash

3、显示/etc/fstab中以#开头，且后面跟一个或多个空白字符，而后又跟了任意非空白字符的行；

[root@openEuler ~]# grep -E "^#[[:space:]]+[^[:space:]]*" /etc/fstab 
# /etc/fstab
# Created by anaconda on Sat Mar 16 12:06:55 2024
# Accessible filesystems, by reference, are maintained under '/dev/disk/'.
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info.
# After editing this file, run 'systemctl daemon-reload' to update systemd
# units generated from this file.

4、查找/etc/rc.d/rc.local中包含“以to开始并以to结尾”的字串行；

[root@openEuler ~]# grep -E "^to.*to$" /etc/rc.d/rc.local
[root@openEuler ~]#

5、查找/etc/inittab中含有“以s开头，并以d结尾的单词”模式的行；

[root@openEuler ~]# grep -Ew "s[[:alpha:]]+d" /etc/inittab 
# 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:

效果如下：

6、查找ifconfig命令结果中的1-255之间的整数；

[root@openEuler ~]# ifconfig | grep -Ew "[1-9]|[1-9][0-9]|1[0-9][0-9]|2[0-5][0-5]" inet 192.168.54.150  netmask 255.255.255.0  broadcast 192.168.54.255inet6 fe80::20c:29ff:fe95:6d47  prefixlen 64  scopeid 0x20<link>ether 00:0c:29:95:6d:47  txqueuelen 1000  (Ethernet)RX packets 4383  bytes 384873 (375.8 KiB)
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536inet 127.0.0.1  netmask 255.0.0.0inet6 ::1  prefixlen 128  scopeid 0x10<host>inet 192.168.122.1  netmask 255.255.255.0  broadcast 192.168.122.255ether 52:54:00:ed:da:6c  txqueuelen 1000  (Ethernet)

效果如下：

7、显示/var/log/secure文件中包含“Failed”或“FAILED”的行；

[root@openEuler ~]# grep -E "(Failed|FAILED)" /var/log/secure
grep: /var/log/secure: binary file matches

注：这里意味着 /var/log/secure 被识别为二进制文件。grep 主要用于处理文本文件，在二进制文件上使用可能会导致不期望的结果或错误。代码应该是没有错的，换一个文件，或者自己创建一个文件练习就可以了。

8、在/etc/passwd中取出默认shell为bash的行；

[root@openEuler ~]# grep -E "bash$" /etc/passwd
root:x:0:0:Super User:/root:/bin/bash
openeuler:x:1000:1000:openEuler:/home/openeuler:/bin/bash
test02:x:1004:1004::/home/test02:/bin/bash
test03:x:1005:1005::/home/test03:/bin/bash

9、以长格式列出/etc/目录下以ns开头、.conf结尾的文件信息；

[root@openEuler ~]# ll /etc/ns*.conf
-rw-r--r--. 1 root root 1516 Mar 16 20:08 /etc/nsswitch.conf

10、高亮显示passwd文件中冒号，及其两侧的字符；

[root@openEuler ~]# grep -E "(:|[^[:space:]]:[^[:space:]])" /etc/passwd
root:x:0:0:Super User:/root:/bin/bash
bin:x:1:1:bin:/bin:/usr/sbin/nologin
daemon:x:2:2:daemon:/sbin:/usr/sbin/nologin
adm:x:3:4:adm:/var/adm:/usr/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/usr/sbin/nologin
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown

效果如下：