Perl 学习手札之十：subroutines
understanding subroutinessubroutines(sometimes called "functions") are a means of encapsulating code.
subroutines are reusable.
subroutines can hide complexity.
subroutines can call other subroutines.
subroutines can call themselves.
this is called "recursion"http://www.cnblogs.com/hanleilei/admin/EditPosts.aspx?IsDraft=1
defining.pl
1 #!/usr/bin/perl
2
3 use strict;
4 use warnings;
5 use subs qw( message error);#加上这个语句，就可以在调用函数的时候去掉括号，否则只能把函数定义放在调用前面
6
7 main(@ARGV);
8
9 sub main
10 {
11 message "This is the template.pl exercise file from Perl 5 Essential Training.";
12 message "message two";
13 error "message three";
14 }
15
16 sub message
17 {
18 my $m = shift or return;
19 print("$m\n");
20 }
21
22 sub error
23 {
24 my $e = shift || 'unkown error';
25 print("$0: $e\n");
26 exit 0;
27 } 注意：上面的例子的message语句是没有括号的，因为从一开始先申明了调用message的子函数，否则需要把申明子函数放在main函数之前。
argument.pl
#!/usr/bin/perl
#
use strict;
use warnings;
main(@ARGV);
sub main
{
my $s = "This is the template.pl exercise file from Perl 5 Essential Training.";
my $y = "42";
my $z = "zee";
message($s,$y,$z);
}
sub message
{
my ($s,$y,$z)= @_;
print("$s,($y),($z)\n");
}
sub error
{
my $e = shift || 'unkown error';
print("$0: $e\n");
exit 0;
} 注意以上的message子函数的参数传递：先传递给一个默认数组，然后传递给标量。
scope.pl
#!/usr/bin/perl
#
use strict;
use warnings;
my $g= "yet other string";
main(@ARGV);
sub main
{
my $m = "some other string";
message("This is the template.pl exercise file from Perl 5 Essential Training.");
message($m);
}
sub message
{
my $m = shift or return;
print("$g:$m\n");
}
sub error
{
my $e = shift || 'unkown error';
print("$0: $e\n");
exit 0;
} 上面的例子描述了标量的作用域。
return.pl
#!/usr/bin/perl
#
use strict;
use warnings;
main(@ARGV);
sub main
{
my $num = addnum(2,4);
message($num);
message(addnum(5,8));
}
sub addnum{
my ($v1,$v2)=@_;
return $v1+$v2;
}
sub message
{
my $m = shift or return;
print("$m\n");
}
sub error
{
my $e = shift || 'unkown error';
print("$0: $e\n");
exit 0;
} 上面的例子描述了子函数的返回值，和C一样
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