perl 第1章 概述

perl 变量语法（标量和数组）

$salar, 标量， @array 数组

类型	字符	例子	用于哪种名字
标量	$	$cents	一个独立的数值（数字或字串）
数组	@	@large	一列数值，用编号做键字
散列	%	%interest	一组数值，用字串做键字
子过程	&	&how	一段可以调用的 Perl 代码
类型团	*	*struck	所有叫 struck 的东西

 

• $answer = 42; # 一个整数
• $pi = 3.14159265 # 一个"实"数
• $pet = "Camel"; # 字串
• $sign = "I ove my $pet"; # 双引号：代换的字串
• $cose = 'It cose $100'; # 单引号：不带代换的字串
• $thence = $whence; # 另一个变量的数值
• $exit = system("set/a 1/0 2>nul"); # 一条命令的数字状态
• $time = `echo %time%`; # 获取windows当前时间

根据环境自动转换类型
$camels = '123';
print $camels +1, "\n";
-----------------------
复数变量 --> 数组的使用：

@home = ("couch", "chair", "table", "stove");
print "@home\n";
($a, $b, $c, $d, $e) = @home;
printf "\$a = $a, \$b = $b, \$c = $c, \$d = $d, \$e = $e";
## 输出：
couch chair table stove
$a = couch, $b = chair, $c = table, $d = stove, $e =

数组元素的获取

@home = ("couch", "chair", "table", "stove");
print "\$home[0] = $home[0], \$home[1] =  $home[1]";
## 输出：
$home[0] = couch, $home[1] =  chair

散列的使用

%longday = (	"Sun", "Sunday", 
		"Mon", "Monday",
		"Tue", "Tuesday",
                "Wed", "Wednesday",
		"Thu", "Thursday",
		"Fri", "Friday",
		"Sat", "Saturday"
	);
# 另外一种写法：
%longday = (
               "Sun" => "Sunday",
               "Mon" => "Monday",
               "Tue" => "Tuesday",
               "Wed" => "Wednesday",
               "Thu" => "Thursday",
               "Fri" => "Friday",
               "Sat" => "Saturday",
                );

散列表元素的获取

#因为是获取标量，因此你在 longday 前面使用 $，而不是 %，% 代表整个散列．

$longday{"Wed"}

散列表的修改

  %longday = (
                      "Sun" => "Sunday",
                      "Mon" => "Monday",
                      "Tue" => "Tuesday",
                      "Wed" => "Wednesday",
                      "Thu" => "Thursday",
                      "Fri" => "Friday",
                      "Sat" => "Saturday",
             );
$longday{"Wed"} = "周3";

print "$longday{\"Wed\"}";

散列表的创建

$wife{"Jacob"} = ["Leah", "Rachel", "Bilhah", "Zilpah"];  
# 相当于：
        $wife{"Jacob"}[0] = "Leah";
        $wife{"Jacob"}[1] = "Rachel";
        $wife{"Jacob"}[2] = "Bilhah";
        $wife{"Jacob"}[3] = "Zilpah";

print $wife{"Jacob"}[0], "";
# 输出：
Leah

# -------------------
  $kids_of_wife{"Jacob"} = {
              "Leah"   => ["Reuben", "Simeon", "Levi", "Judah", "Issachar", "Zebulun"],
              "Rachel" => ["Joseph", "Benjamin"],
              "Bilhah" => ["Dan", "Naphtali"],
              "Zilpah" => ["Gad", "Asher"],};

print $kids_of_wife{"Jacob"}{"Leah"}[0], "";
# 输出：
Reuben

chop($number = <STDIN>); # 输入数字并删除新行
另外一种写法：

$number = <STDIN>; # 输入数字
chop($number); # 删除新行

. 操作符 (.) 来完成字符串的串联，这样就不会跟数字的加号相混淆。

   $a = 123;
   $b = 456;
   print $a + $b;      # 打印 579
   print $a . $b;      # 打印 123456

x 操作符

$a = 50;
print "-" x $a;
# 输出：
--------------------------------------------------

文件

   open(SESAME, "filename")         # 从现存文件中读取
   open(SESAME, "<filename")         # （一样的东西，明确地做）
   open(SESAME, ">filename")         # 创建文件并写入
   open(SESAME, ">>filename")         # 附加在现存文件后面
   open(SESAME, "| output-pipe-command")   # 设置一个输出过滤器
   open(SESAME, "input-pipe-command |")      # 设置一个输入过滤器

自操作元素符：　　

  $a *= 3;
# 你可读成“用 3 乘 $a”。
# Perl 中大多数的双目操作符都可以这么使用，甚至有些你在 c 语言中不能使用的也可以在 Perl 使用： 
   $line .= "\n";      # 给 $line 附加一个新行
   $fill x=80;      # 把字串变成自填充 80 遍
   $val ||= "2";      # 如果 $val 不为真则把它设置为 2

　　

# 词频统计


open(fd, "a.c");
while($line = <fd>){
	foreach $word (split /[^A-Za-z]/, $line) {
		$count{$word}++;
	}
}

foreach $word (keys %count) {
	printf("%-16s %5s\n",$word, $count{$word});
}
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