use strict;
use warnings;

my $a = 10;
my $b = 3;

printf "%d + %d = %d\n", $a, $b, $a + $b;
printf "%d - %d = %d\n", $a, $b, $a - $b;
printf "%d * %d = %d\n", $a, $b, $a * $b;
printf "%d / %d = %.2f\n", $a, $b, $a / $b;
printf "%d %% %d = %d\n", $a, $b, $a % $b;
printf "%d ** %d = %d\n", 2, 10, 2 ** 10;

# 自增自减
my $x = 5;
print $x++, "\n";   # 输出 5，然后 $x 变为 6
print $x, "\n";     # 输出 6
print ++$x, "\n";   # $x 变为 7，输出 7

# 拼接
my $greeting = "Hello" . " " . "World" . "!";
print "$greeting\n";   # Hello World!

# 重复
my $line = "-" x 40;
print "$line\n";        # ----------------------------------------

# 字符串比较
my $a = "apple";
my $b = "banana";

if ($a lt $b) {
    print "$a 在 $b 前面（字典序）\n";
}

# cmp 三路比较
my $result = $a cmp $b;
print "比较结果: $result\n";   # -1（$a < $b）

# 这是 Perl 新手最容易犯的错误！
my $x = "02";
my $y = "10";

# 字符串比较（字典序）
print "字符串: $x eq $y ? ", ($x eq $y ? "是" : "否"), "\n";  # 否
print "字符串: $x gt $y ? ", ($x gt $y ? "是" : "否"), "\n";  # 是（'0' > '1' 错误，实际 '02' gt '10' 因为 '0' < '1'）

# 数值比较
print "数值: $x == $y ? ", ($x == $y ? "是" : "否"), "\n";    # 否
print "数值: $x > $y ? ", ($x > $y ? "是" : "否"), "\n";      # 否

# 正确理解：
# "02" lt "10" 因为 '0' 的 ASCII 码 (48) < '1' 的 ASCII 码 (49)
# 2 < 10 数值上

# 传统风格（优先级高）
my $x = $a && $b;         # $a 为真则返回 $b，否则返回 $a
my $y = $a || $b;         # $a 为真则返回 $a，否则返回 $b

# 词组风格（优先级低，适合流程控制）
open my $fh, '<', 'file.txt' or die "无法打开: $!\n";
send_email($to, $body) and log("邮件已发送");

# && 返回第一个假值或最后一个值
print 0 && "hello";       # 0
print 1 && "hello";       # "hello"
print "a" && "b" && "c";  # "c"

# || 返回第一个真值或最后一个值
print 0 || "hello";       # "hello"
print "a" || "b";         # "a"
print 0 || "" || undef;   # undef

# // (Perl 5.10+) - 定义或运算符
# 返回第一个已定义的值
my $name = $input // "默认值";   # $input 未定义则用默认值

my $perms = 0755;
printf "权限: %04o\n", $perms;      # 0755
printf "所有者: %03o\n", ($perms >> 6) & 07;
printf "组: %03o\n", ($perms >> 3) & 07;
printf "其他: %03o\n", $perms & 07;

# 默认值设置
my $name = $ENV{USER} // "anonymous";
my $count ||= 0;   # 如果未定义则设为 0

# 字符串构建
my $html = "";
$html .= "<h1>标题</h1>\n";
$html .= "<p>内容</p>\n";

my @nums = 1..10;            # (1, 2, 3, ..., 10)
my @reverse = 10..1;         # () 空！范围必须从小到大
my @letters = 'a'..'z';      # (a, b, c, ..., z)

# 打印第 3 到第 7 行
while (<STDIN>) {
    print if 3..7;
}

# 打印从 START 到 END 之间的内容
while (<STDIN>) {
    print if /^START/ .. /^END/;
}

my $age = 20;
my $status = ($age >= 18) ? "成年人" : "未成年人";
print "$status\n";

# 嵌套三元（不推荐过度嵌套）
my $level = ($score >= 90) ? "优秀"
          : ($score >= 80) ? "良好"
          : ($score >= 60) ? "及格"
          :                  "不及格";

my $email = "[email protected]";

# 匹配
if ($email =~ /^[\w.]+@[\w.]+\.\w+$/) {
    print "有效的邮箱地址\n";
}

# 不匹配
if ($email !~ /spam/i) {
    print "不是垃圾邮件\n";
}

# 替换
(my $redacted = $email) =~ s/^(.{3}).*/$1***@***/;
print "$redacted\n";   # use***@***

# 逗号 , 是列表运算符
my @list = (1, 2, 3);

# 胖箭头 => 自动为左侧加引号
my %hash = (
    name  => "Perl",       # 等价于 "name" => "Perl"
    year  => 1987,
    motto => "TMTOWTDI",
);

# 不清晰
my $result = $a + $b * $c;

# 清晰明了
my $result = $a + ($b * $c);

#!/usr/bin/env perl
use strict;
use warnings;

# 简单的模板变量替换引擎
sub render_template {
    my ($template, %vars) = @_;

    # 替换 {{variable}} 占位符
    $template =~ s/\{\{(\w+)\}\}/$vars{$1} // "{{$1}}"/ge;

    # 替换 {{if condition}}...{{/if}}
    $template =~ s/\{\{if (\w+)\}\}(.*?)\{\{\/if\}\}/
        $vars{$1} ? $2 : ""/ges;

    return $template;
}

my $tpl = <<'TEMPLATE';
<h1>{{title}}</h1>
<p>作者: {{author}}</p>
{{if published}}<span class="badge">已发布</span>{{/if}}
TEMPLATE

my %data = (
    title     => "Perl 入门教程",
    author    => "张三",
    published => 1,
);

print render_template($tpl, %data);