[shell]用eval和不用eval的几点区别

1.

/home/lee#n=1
/home/lee#echo 'a
> b
> c
> e'>txt
/home/lee#while read line;do var$n=$line;((n++));done

2,
#这里的eval多余的
/home/lee#cmd=date
/home/lee#$cmd     
二  1月 17 13:46:14 CST 2006
/home/lee#eval $cmd 
二  1月 17 13:47:00 CST 2006
/home/lee#$cmd
二  1月 17 13:47:03 CST 2006
#这里用不用eval多余么?
/home/lee#cmd="date;date"
/home/lee#$cmd
ksh: date;date: not found
/home/lee#eval $cmd
二  1月 17 13:47:43 CST 2006
二  1月 17 13:47:43 CST 2006


3,
#这个是比较经典的eval用法了:hat: 
/home/lee#a=123
/home/lee#b=a
/home/lee#echo $b
a
/home/lee#eval echo \$$b
123
/home/lee#