文件中两行互换的shell脚本

代码:

#!/bin/ksh
(($#!=3))&&{ echo Usage:$(basename $0) num1 num2 filename;exit 1; }
num=$(cat $3|wc -l)
n=1
while ((n<=$num))
do
case $n in
        $1)     cat $3|sed -n ${2}p ;;
        $2)     cat $3|sed -n ${1}p ;;
        *)      cat $3|sed -n ${n}p ;;
esac
((n+=1))
done