for空行的特性

for_null.sh内容：

 1 #!/bin/bash
 2 #for null line
 3 #version 1.0 by feng
 4 
 5 IFS=$'
'
 6 for i in `cat $1`
 7 do
 8     if [ ${#i} -eq 0 ];then
 9         echo "the line is null"
10     else
11         echo "$i"
12     fi
13 done

1 [root@localhost for]# cat a.txt 
2 feng 123
3 
4 xiao 456
5     
6           
7 [root@localhost for]# cat for_null.sh

[root@localhost for]# cat -A -n a.txt
1 feng 123$
2 $
3 xiao 456$
4 $
5 ^I^I $

1 [root@localhost for]# sh for_null.sh a.txt 
2 feng 123
3 xiao 456
4     
5           
6 [root@localhost for]#

可以发现，for循环的特点：当以回车作为分隔符时，此处的方式为 for i in "feng 123" 此处多了一个回车分隔符 "xiao 456" " " (引号中为空格) " 　　"(引号中为空格和tab键) 的取值特点。