for空行的特性

 1 #!/bin/bash
 2 #for null line
 3 #version 1.0 by feng
 4 
 5 IFS=$‘\n‘
 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]#