不懂遞歸不算是合格的程序員

遞歸調用是一種特殊的嵌套調用，是一個函數在它的函數體內調用它自身稱為遞歸調用。這種函數稱為遞歸函數。

		
#!/bin/bash
########################################
# Author: Neo <netiller@msn.com>
# Home : http://netkiler.github.io
# Project: https://github.com/oscm/shell
########################################
domain=$1
########################################
function include(){
	txt=$1
	for host in $(echo $txt | egrep -o "include:(.+) ")
	do
		txt=$(dig $(echo $host | cut -d":" -f2) txt | grep "v=spf1")
		echo $txt;
		if [ "$(echo $txt | grep "include")" ]; then
			include "$txt"
		fi
	done
}
function main(){
	spf=$(dig ${domain} txt | grep "v=spf1")
	echo $spf

	if [ "$(echo $spf | grep "include")" ]; then
		include "$spf"
	fi
}

main $domain
		
		

運行上面的程序

		
$ bash spf.sh 163.com
163.com. 6878 IN TXT "v=spf1 include:spf.163.com -all"
spf.163.com. 16991 IN TXT "v=spf1 include:a.spf.163.com include:b.spf.163.com include:c.spf.163.com include:d.spf.163.com -all"
a.spf.163.com. 8001 IN TXT "v=spf1 ip4:220.181.12.0/22 ip4:220.181.31.0/24 ip4:123.125.50.0/24 ip4:220.181.72.0/24 ip4:123.58.178.0/24 ip4:123.58.177.0/24 ip4:113.108.225.0/24 ip4:218.107.63.0/24 ip4:123.58.189.128/25 -all"
b.spf.163.com. 10131 IN TXT "v=spf1 ip4:176.34.21.58 ip4:176.34.53.178 ip4:121.195.178.48/28 ip4:223.252.213.0/24 -all"
c.spf.163.com. 17199 IN TXT "v=spf1 ip4:223.252.206.0/24 ip4:43.230.90.0/27 -all"
d.spf.163.com. 17615 IN TXT "v=spf1 ip4:123.126.65.0/24 ip4:106.2.88.0/24 ip4:220.181.97.0/24 ip4:180.150.142.123 ip4:180.150.142.124 ip4:180.150.154.88 ip4:180.150.154.92 ip4:180.150.154.93 ip4:103.251.128.69 -all"