perl笔记 stdin

#!perl -w
#错误的写法 $line=chomp(<STDIN>);
#正确的写法：
chomp($line=<STDIN>);
if(!$line){
print "you just enter nothing \n";
}else{
print "what you entered is：$line \n";
}
#defined函数
$line2=undef;
if(defined($line2)){
print "it is $line2";
}else{
print "it is undef";
}
#windows ctrl +z,  Linux ctrl+d
chomp(@lines=<STDIN>);
print "@lines";

#god, what am i doing?