高级编程<1>

$a[$i]   @a[$i]子函数:[oracle@jhoa 1]$ cat 2.pl sub hi {my $name = shift;return "hi,$name\n";}print &hi("Fred");[oracle@jhoa 1]$ perl 2.pl hi,Fred[oracle@jhoa 1]$ cat 3.pl while ( my $file = glob('*')) {# print "$file\n";}[oracle@jhoa 1]$ perl 3.pl 1.pl2.pl3.pla.txtunless 条件为假才执行:[oracle@jhoa 1]$ cat a1.pl $var="a1";unless ($var eq "a1"){print "11111\n";}else{print "22222\n";}[oracle@jhoa 1]$ perl a1.pl 22222-----------------------------[oracle@jhoa 1]$ cat a1.pl $var="a1";unless ($var eq "a2"){print "11111\n";}else{print "22222\n";}[oracle@jhoa 1]$ perl a1.pl 11111[oracle@jhoa 1]$ cat a2.pl @cats = qw(a b c d e f g);$cats[1] = undef;print "@cats\n";foreach my $cat (@cats){next unless defined $cat;print "I Have a cat named $cat\n";}[oracle@jhoa 1]$ perl a2.pl a  c d e f gI Have a cat named aI Have a cat named cI Have a cat named dI Have a cat named eI Have a cat named fI Have a cat named g--------------------------------------------------defined 测试该元素的值用exists 函数测试是否存在该键名[oracle@jhoa 1]$ cat a3.pl my %hash;if ( $hash{'foo'}){print "1111\n"};if (defined  $hash{'foo'}){print "2222\n"};if (exists  $hash{'foo'}){print "3333\n"};[oracle@jhoa 1]$ perl a3.pl [oracle@jhoa 1]$ 全部为假:[oracle@jhoa 1]$ cat a3.pl  my %hash;$hash{'foo'}= undef;if ( $hash{'foo'}){print "1111\n"};if (defined  $hash{'foo'}){print "2222\n"};if (exists  $hash{'foo'}){print "3333\n"}; 为真[oracle@jhoa 1]$ perl a3.pl 3333