请高手给解释一下此脚本的意思?

jellychen

这是一个Iptables的脚本,对其不解,所以请高手帮忙,内容如下:
#!/bin/sh
IN_TCP_PORTALLOWED="ssh,192.168.8.1 domain smtp http https"
for i in $IN_TCP_PORTALLOWED ; do
   IFS=','
   set $i

   unset IFS ipt_option
   port="$1"

   [ -n "$2" ] && ipt_option="-s `echo $2 | sed 's/^!/! /'`"
   iptables -A INPUT -p tcp $ipt_option --dport $port \
         --syn -m state --state NEW -j ACCEPT
done
我想问的问题如下:
1: set $i 是什么意思?
2: unset IFS ipt_option 中的ipt_option从何而来?什么意思?unset ipt_option之后其值会发生什么变化?
感谢!

jellychen

为什么?
各位高手!
帮帮忙!

yongjian

1. set $i means assign the value of $i to positional argus $1, $2...
2. unset will clean the value of a variable. because the whole thing runs in a loop and using the same variable, so everytime it loops to the next, the value of the variable should be cleaned and then assigned to a new value.

jellychen

I see.
Thanks a lot!