perl undef $/

Sample Code  
 undef $/;  
  Based on the code sample above, what is the effect during input or output?  
Choice 1   
 It reads the entire file.  
Choice 2   
 It specifies to Perl not to buffer file output.  
Choice 3   
 It displays a line at a time in output.  
Choice 4   
 It reads a line at a time.  
Choice 5   
 It makes later processing case insensitive.

答案：choice 1

上一个：keil编译的C程序，不知道是啥错误,求帮忙。单片机STC89C52
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