比较变量时如何省略某个字符串？

Question

我试图在 if/else 语句中省略广播 IP 地址 (192.168.0.255)。

我想从 (newo) 变量中省略广播 ip。

由于我还在学习，请对我轻点。如果有其他方法可以压缩此工作流程，请告诉我。谢谢。 :)

 bcast="$(ifconfig | grep broadcast | awk '{print $6}')"  
 oldo="$(arp -a)"
 ping -c 1 "$bcast"  
 sleep 3
 killall ping
 newo="$(arp -a)"

 if [ "$oldo" = "$newo" ] 
 then
     echo="match"
 else
     echo="no match"
 fi

旁注： 当我 ping 广播时，这就是它显示在 (newo) 变量中的原因。这将是我在比较两者时忽略该字符串的原因。

结果： 出于隐私考虑，我省略了所有 MAC 地址。

++ ifconfig
++ grep broadcast
++ awk '{print $6}'
+ bcast=192.168.0.255
++ arp -a
+ oldo='? (192.168.0.1) at on en1 ifscope [ethernet]
? (192.168.0.11) at on en1 ifscope [ethernet]
? (192.168.0.14) at on en1 ifscope [ethernet]
? (192.168.0.15) at on en1 ifscope [ethernet]
? (192.168.0.17) at on en1 ifscope [ethernet]
? (192.168.0.19) at on en1 ifscope [ethernet]
? (192.168.0.20) at on en1 ifscope [ethernet]
? (192.168.0.22) at on en1 ifscope permanent [ethernet]
? (192.168.0.25) at on en1 ifscope [ethernet]
? (192.168.0.255) at ff:ff:ff:ff:ff:ff on en1 ifscope [ethernet]
? (224.0.0.251) at on en1 ifscope permanent [ethernet]
? (239.255.255.250) at on en1 ifscope permanent [ethernet]'
+ ping -c 1 192.168.0.255
PING 192.168.0.255 (192.168.0.255): 56 data bytes
64 bytes from 192.168.0.22: icmp_seq=0 ttl=64 time=0.155 ms

--- 192.168.0.255 ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.155/0.155/0.155/0.000 ms
+ sleep 3
+ killall ping
No matching processes belonging to you were found
++ arp -a
+ newo='? (192.168.0.1) at on en1 ifscope [ethernet]
? (192.168.0.11) at on en1 ifscope [ethernet]
? (192.168.0.14) at on en1 ifscope [ethernet]
? (192.168.0.15) at on en1 ifscope [ethernet]
? (192.168.0.17) at on en1 ifscope [ethernet]
? (192.168.0.19) at on en1 ifscope [ethernet]
? (192.168.0.20) at on en1 ifscope [ethernet]
? (192.168.0.22) at on en1 ifscope permanent [ethernet]
? (192.168.0.25) at on en1 ifscope [ethernet]
? (192.168.0.255) at ff:ff:ff:ff:ff:ff on en1 ifscope [ethernet]
? (224.0.0.251) at on en1 ifscope permanent [ethernet]
? (239.255.255.250) at on en1 ifscope permanent [ethernet]'
+ '[' '? (192.168.0.1) at on en1 ifscope [ethernet]
? (192.168.0.11) at on en1 ifscope [ethernet]
? (192.168.0.14) at on en1 ifscope [ethernet]
? (192.168.0.15) at on en1 ifscope [ethernet]
? (192.168.0.17) at on en1 ifscope [ethernet]
? (192.168.0.19) at on en1 ifscope [ethernet]
? (192.168.0.20) at on en1 ifscope [ethernet]
? (192.168.0.22) at on en1 ifscope permanent [ethernet]
? (192.168.0.25) at on en1 ifscope [ethernet]
? (192.168.0.255) at ff:ff:ff:ff:ff:ff on en1 ifscope [ethernet]
? (224.0.0.251) at  on en1 ifscope permanent [ethernet]
? (239.255.255.250) at  on en1 ifscope permanent [ethernet]' = '? (192.168.0.1) at  on en1 ifscope [ethernet]
? (192.168.0.11) at  on en1 ifscope [ethernet]
? (192.168.0.14) at  on en1 ifscope [ethernet]
? (192.168.0.15) at  on en1 ifscope [ethernet]
? (192.168.0.17) at  on en1 ifscope [ethernet]
? (192.168.0.19) at  on en1 ifscope [ethernet]
? (192.168.0.20) at  on en1 ifscope [ethernet]
? (192.168.0.22) at  on en1 ifscope permanent [ethernet]
? (192.168.0.25) at  on en1 ifscope [ethernet]
? (192.168.0.255) at ff:ff:ff:ff:ff:ff on en1 ifscope [ethernet]
? (224.0.0.251) at  on en1 ifscope permanent [ethernet]
? (239.255.255.250) at  on en1 ifscope permanent [ethernet]' ']'
+ echo=match

Answer 1

如果您只是想确保广播地址不会出现在newo 中，请尝试：

bcast=$(ifconfig | awk '/broadcast/{print $6}')  
newo=$(arp -a | awk '!match($2,"("b")")' b=$bcast)