awk命令過濾ifconfig命令中的IPv4地址

前言：

????????本文主要講解如何過濾ifconfig命令結果中的IPv4地址。

????????本文章的案例適合查找出所有網卡的IPv4地址。

????????本章所有案例的系統是Red Hat 7.6版本。

[root@192?opt]#?cat?/etc/redhat-release?
Red?Hat?Enterprise?Linux?Server?release?7.6?(Maipo)

方法一：

? ? ? ? 使用awk命令、正則表達式、通配符來篩選IPv4地址。

[root@localhost?~]#?ifconfig
ens33:?flags=4163<UP,BROADCAST,RUNNING,MULTICAST>??mtu?1500
????????inet?192.168.109.128??netmask?255.255.255.0??broadcast?192.168.109.255
????????inet6?fe80::20c:29ff:fed8:33c3??prefixlen?64??scopeid?0x20<link>
????????ether?00:0c:29:d8:33:c3??txqueuelen?1000??(Ethernet)
????????RX?packets?22836??bytes?1608781?(1.5?MiB)
????????RX?errors?0??dropped?0??overruns?0??frame?0
????????TX?packets?6159??bytes?617125?(602.6?KiB)
????????TX?errors?0??dropped?0?overruns?0??carrier?0??collisions?0

lo:?flags=73<UP,LOOPBACK,RUNNING>??mtu?65536
????????inet?127.0.0.1??netmask?255.0.0.0
????????inet6?::1??prefixlen?128??scopeid?0x10<host>
????????loop??txqueuelen?1000??(Local?Loopback)
????????RX?packets?0??bytes?0?(0.0?B)
????????RX?errors?0??dropped?0??overruns?0??frame?0
????????TX?packets?0??bytes?0?(0.0?B)
????????TX?errors?0??dropped?0?overruns?0??carrier?0??collisions?0

[root@localhost?~]#?ifconfig|awk?'/inet?/?&&?$2?!~?/^127/{print?$2}'
192.168.109.128

????????注釋：awk命令用正則來過濾出有IP地址的行并且用通配符來排除以127開頭（回環地址）的地址，最后打印出第二列的有效IP地址。

方法二：

????? ? 結合使用awk命令和grep命令來過濾IPv4地址。

[root@localhost?~]#?ifconfig
ens33:?flags=4163<UP,BROADCAST,RUNNING,MULTICAST>??mtu?1500
????????inet?192.168.109.128??netmask?255.255.255.0??broadcast?192.168.109.255
????????inet6?fe80::20c:29ff:fed8:33c3??prefixlen?64??scopeid?0x20<link>
????????ether?00:0c:29:d8:33:c3??txqueuelen?1000??(Ethernet)
????????RX?packets?24068??bytes?1711773?(1.6?MiB)
????????RX?errors?0??dropped?0??overruns?0??frame?0
????????TX?packets?6769??bytes?690417?(674.2?KiB)
????????TX?errors?0??dropped?0?overruns?0??carrier?0??collisions?0

lo:?flags=73<UP,LOOPBACK,RUNNING>??mtu?65536
????????inet?127.0.0.1??netmask?255.0.0.0
????????inet6?::1??prefixlen?128??scopeid?0x10<host>
????????loop??txqueuelen?1000??(Local?Loopback)
????????RX?packets?0??bytes?0?(0.0?B)
????????RX?errors?0??dropped?0??overruns?0??frame?0
????????TX?packets?0??bytes?0?(0.0?B)
????????TX?errors?0??dropped?0?overruns?0??carrier?0??collisions?0

[root@localhost?~]#?ifconfig|awk?'{match($0,/[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+/);print?substr($0,RSTART,RLENGTH)}'|grep?-Ev?"^127|^$"
192.168.109.128

????????注釋：先使用awk中match命令結合正則查找出IP地址格式的字符串所在行的位置和長度，再用substr命令來截取IP地址，最后使用grep命令排除以127開頭（回環地址）和空行并打印出其它所有的IP地址。

方法三：

????????使用awk命令中RS變量的特殊值和正則匹配來篩選出IPv4地址。

[root@localhost?~]#?ifconfig
ens33:?flags=4163<UP,BROADCAST,RUNNING,MULTICAST>??mtu?1500
????????inet?192.168.109.128??netmask?255.255.255.0??broadcast?192.168.109.255
????????inet6?fe80::20c:29ff:fed8:33c3??prefixlen?64??scopeid?0x20<link>
????????ether?00:0c:29:d8:33:c3??txqueuelen?1000??(Ethernet)
????????RX?packets?24536??bytes?1748017?(1.6?MiB)
????????RX?errors?0??dropped?0??overruns?0??frame?0
????????TX?packets?6958??bytes?712613?(695.9?KiB)
????????TX?errors?0??dropped?0?overruns?0??carrier?0??collisions?0

lo:?flags=73<UP,LOOPBACK,RUNNING>??mtu?65536
????????inet?127.0.0.1??netmask?255.0.0.0
????????inet6?::1??prefixlen?128??scopeid?0x10<host>
????????loop??txqueuelen?1000??(Local?Loopback)
????????RX?packets?0??bytes?0?(0.0?B)
????????RX?errors?0??dropped?0??overruns?0??frame?0
????????TX?packets?0??bytes?0?(0.0?B)
????????TX?errors?0??dropped?0?overruns?0??carrier?0??collisions?0

[root@localhost?~]#?ifconfig|awk?'BEGIN{RS=""}!/^lo/{print?$6}'
192.168.109.128

????????注釋：先使用BEGIN來定義RS變量的值為段落分隔（BEGIN{RS=""}），然后用正則匹配來排除以lo開頭的段落，最后找出IP地址所在列的位置并打印出來。本方法要確保IP地址要在段落的第六列，當然也可以根據自己的特殊情況來進行調整。

????????RS變量：通俗講就是換行分隔符變量，默認值為"\n"換行符，而awk命令一次性讀取多少數據都是由RS變量來決定的。例如：RS=" "（空格），awk一次性讀取的數據為一個字符串 不再是一行的數據了。

????????RS=""（中間沒有空格）：此為RS變量的特殊值（段落分隔），以空行或多個連續空行為分隔，一次性讀取一段數據。

方法四：

????????使用awk命令中的RS和FS變量來篩選出ipv4地址（本方法比較復雜，主要講的是awk的使用）

[root@localhost?~]#?ifconfig
ens33:?flags=4163<UP,BROADCAST,RUNNING,MULTICAST>??mtu?1500
????????inet?192.168.109.128??netmask?255.255.255.0??broadcast?192.168.109.255
????????inet6?fe80::20c:29ff:fed8:33c3??prefixlen?64??scopeid?0x20<link>
????????ether?00:0c:29:d8:33:c3??txqueuelen?1000??(Ethernet)
????????RX?packets?25278??bytes?1804185?(1.7?MiB)
????????RX?errors?0??dropped?0??overruns?0??frame?0
????????TX?packets?7240??bytes?745239?(727.7?KiB)
????????TX?errors?0??dropped?0?overruns?0??carrier?0??collisions?0

lo:?flags=73<UP,LOOPBACK,RUNNING>??mtu?65536
????????inet?127.0.0.1??netmask?255.0.0.0
????????inet6?::1??prefixlen?128??scopeid?0x10<host>
????????loop??txqueuelen?1000??(Local?Loopback)
????????RX?packets?0??bytes?0?(0.0?B)
????????RX?errors?0??dropped?0??overruns?0??frame?0
????????TX?packets?0??bytes?0?(0.0?B)
????????TX?errors?0??dropped?0?overruns?0??carrier?0??collisions?0

[root@localhost?~]#?ifconfig|awk?'BEGIN{RS="";FS="\n"}!/^lo/{$0=$2;FS="?";$0=$0;print?$2}'
192.168.109.128

????????注釋：先使用BEGIN定義awk以段落來讀取數據，列以換行符來分隔（BEGIN{RS="";FS="\n"}）。再使用正則匹配排除以lo開頭的段落。重新設置$0的值為$2（含有IP地址的那一行內容，此時列的分隔符為換行符），設置FS變量的值為空格（FS=" "，列分隔符為空格），再重新設置$0的值但保持內容不變（$0=$0，重置FS的值），最后打印出IP地址。

????????FS變量：列的分隔符變量。$0=$2或$2=xxx或$6=$8等等只要重置了$0或列的內容都會重置一次FS變量的值。

方法五：

????????結合使用awk和sed命令來過濾IPv4地址。

[root@localhost?~]#?ifconfig
ens33:?flags=4163<UP,BROADCAST,RUNNING,MULTICAST>??mtu?1500
????????inet?192.168.109.128??netmask?255.255.255.0??broadcast?192.168.109.255
????????inet6?fe80::20c:29ff:fed8:33c3??prefixlen?64??scopeid?0x20<link>
????????ether?00:0c:29:d8:33:c3??txqueuelen?1000??(Ethernet)
????????RX?packets?26232??bytes?1879377?(1.7?MiB)
????????RX?errors?0??dropped?0??overruns?0??frame?0
????????TX?packets?7636??bytes?791883?(773.3?KiB)
????????TX?errors?0??dropped?0?overruns?0??carrier?0??collisions?0

lo:?flags=73<UP,LOOPBACK,RUNNING>??mtu?65536
????????inet?127.0.0.1??netmask?255.0.0.0
????????inet6?::1??prefixlen?128??scopeid?0x10<host>
????????loop??txqueuelen?1000??(Local?Loopback)
????????RX?packets?0??bytes?0?(0.0?B)
????????RX?errors?0??dropped?0??overruns?0??frame?0
????????TX?packets?0??bytes?0?(0.0?B)
????????TX?errors?0??dropped?0?overruns?0??carrier?0??collisions?0

[root@localhost?~]#?ifconfig|sed?-n?'/inet?/p'|awk?'$2?!~?/^127/{print?$2}'
192.168.109.128

????????注釋：先用sed命令過濾出包含IP地址的行，再使用awk命令排除含有以127開頭（回環地址）IP地址的行，最后打印其他行的有效的IP地址。

總結：

????????本文章主要使用awk命令來篩選IPv4地址。

????????涉及到awk命令的功能主要如下所示：

????????????????RS變量：行分隔符變量，就是一次性讀取的數據由此變量來決定。

????????????????FS變量：列分隔符變量，每一列的內容由此變量來進行分隔。

????????????????match命令：查找所匹配格式的字符串在每行中的位置，以及所匹配到的字符串的長度。

????????????????substr命令：根據條件來截取數據。命令格式：substr("原始數據","開始位置","結束位置")，位置主要以數字來定義。沒有結束位置則截取到原始數據的末尾。