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 = $home, \$home =$home";
## 输出：
$home = couch, $home =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"} = "Leah";
$wife{"Jacob"} = "Rachel";
$wife{"Jacob"} = "Bilhah";
$wife{"Jacob"} = "Zilpah";
print $wife{"Jacob"}, "";
# 输出：
Leah
# -------------------
$kids_of_wife{"Jacob"} = {
"Leah" => ["Reuben", "Simeon", "Levi", "Judah", "Issachar", "Zebulun"],
"Rachel" => ["Joseph", "Benjamin"],
"Bilhah" => ["Dan", "Naphtali"],
"Zilpah" => ["Gad", "Asher"],};
print $kids_of_wife{"Jacob"}{"Leah"}, "";
# 输出：
Reuben
chop($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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