1、变量

$price = 11.0;
$name = "lisi";
$var = "hello"."world"; # "helloworld"  字符串连接
$name = "i am $name " # "i am lisi "  #变量内插  
# 没有布尔数据类型， 数字0为假，非0为真，非空字符串为真，除了"0",这个会转换为数字0，所以为假

1.1、哈希

my $hash=(
    a => 1,
    b => 2,
    c => "sdf",
);
my @k = keys %hash;
my @v = values %hash;

#!/usr/bin/perl
print "PATH is $ENV{PATH}\n";
print "while循环，取出键值对\n";
while (($key,$value)=each %ENV){
    print "$key => $value\n";
}
print "foreach 循环，取出键，通过键获取值\n";
foreach $key (keys %ENV){
    print "$key => $ENV{$key}\n";
}

2、程序结构

2.1、分支

#!/usr/bin/perl
$line = <STDIN>;
if($line eq "\n"){
    print "That was just a blank line !\n";
} else {
    print "That line of input was :$line";
}

2.2、循环

#!/usr/bin/perl
$count = 0 ;
while($count < 10){
    $count +=2;
    print "count is now $count\n";
}

3、函数

3.1、去除末尾换行符

chomp($text);
chomp $text
chomp($text=<STDIN>);
# 结尾有多个换行符，也仅仅删除一个，如果没有，它什么也不做，直接返回0.返回值为删除的字符数。

3.2、输入

$line = <STDIN>;

4、子程序

#!/usr/bin/perl
use strict;
sub total {
    my $sum = 0;
    foreach my $num (@_){
        print "$num\n";
        $sum += $num;
    }
    print "$sum\n";
    return $sum;
}
my @fred = 1..100;
my $fred_total = total(@fred);
print "The total of \@fred is $fred_total.\n";

use strict;
sub avg {
    my $sum = 0;
    foreach my $num (@_){            # @_表示参数列表
        $sum += $num;
    }
    print "$sum\n";
    return $sum/@_;
}
above_average(1..100);
sub above_average {
    my $avg_num = avg(@_);
    my @list;
    foreach (@_){
        if ($_ > $avg_num){              # 循环的控制变量默认为$_
            push @list , $_ ; 
        }
    }
    print "@list\n";
}
above_average(2,2,4,5);

#!/usr/bin/perl
use 5.010;
sub greet {
    state $last_person;  # 持久的私有变量
    my $name = shift;     
    print "Hi $name!\n";
    if(defined $last_person){
        print "$last_person is also here!\n";
    }else{
        print "You are the first one here\n";
    }
    $last_person=$name;
}
greet("lisi");
greet("sss");