test_1.pl

#/usr/bin/perl -wuse strict;print add(1,2),"\n";sub add {  my ($x,$y) = @_;    return $x + $y; # When Perl reaches any return statement it will exit the subroutine at that point.  print "Hello World\n";}

perl test_1.pl # 3

test_2.pl

#/usr/bin/perl -wuse strict;print add(1,2),"\n";sub add {  my ($x,$y) = @_;    $x + $y;  print "Hello World\n";}

perl test_2.pl # Hello World 和 1，还有报错（默认 return sub 中的最后一行；print add(1,2) 则打印出"1"）