Perl basic grammar

标量数据

perlThe scalar in language is mostlydigital scalar和字符串标量.

1. 数字

• 浮点数
  3.25e20 (3.25乘10的20次方）
• 整数
  1415926 1_415_926 （perlUnderscores are allowed between integers for clear identification）
• 数字运算符

注意：perlInteger and floating point numbers in are as perdoublestorage calculation.

2. 字符串

• 单引号
  where string is the string itself,不会转义.
• 双引号
  \会转义
• Period operator.
  Strings before and after concatenation
• 重复操作符x
  copy字符串,如果copyThe number of times is a decimal,则向下取整
• 数字与字符串之间的转换
  perlThe data conversion is done by itself according to the operator

3. 标量变量

• 命名规则
  以$开头;
  Variable identifiers consist of alphanumeric underscores,但不能以数字开头;
  变量区分大小写;
• 等号赋值
• Binary assignment operator
  += -= *= /= %=
• String variable interpolation
• Numeric scalar and character scalar comparison operators

• chomp函数
  Remove newlines at the end of a string
• chop函数
  Remove characters from the end of the string
• substr函数
  Take out some characters,Returns the extracted string

substr EXPR,OFFSET,LENGTH,REPLACEMENT
#EXPR String handle
#OFFSET 处理起始位置,默认为0,Negative numbers are counted from the right
#LENGTH 处理长度,负数时,从右侧数LENGTH个点,Take the characters between this point and the starting point,From start to end when not provided
#REPLACEMENT 替换字符串

• split Split the string into an array

split /pattern/, EXPR, LIMIT
#if only pattern is given, EXPR defaluts to $_
#pattern 分隔符,Regular when possible,也可以指定,defaluts为" ",省略分隔符,Consecutive whitespace is considered a single delimiter
#LIMIT 限制数组长度,Default maximum number of splits

• join Inserts the given character into an array,转换为字符串

数组和哈希

1. 数组

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

my $scalar = "wow";
#数组定义
my @array = (1, "str", $scalar);

#元素调用
print "$array[0]\n";

#元素连接
my $array_str = join "\t", @array;
print "$array_str\n"

#数组长度 方法一
my $len = $#array + 1;
print "$len\n";

#数组长度 方法二
my $len2 = scalar @array; #scalar可以省略
print "$len2\n";

#遍历数组 方法一 
foreach (@array)
{
    
	print "$_\n" #$_ Indicates the default place,foreach No readout element specified,就存在$_中
}

#遍历数组 方法二
foreach (0..$#array)
{
    
	print "$array[$_]\n";
}

#数组末尾添加元素 push
push @array, "push";
print "@array\n";

#Remove elements from the end of the array pop
pop @array;
print "@array\n";

#Add elements to the beginning of the array unshift
unshift @array, "unshift";
print "@array\n";

#数组开头删除元素 shift
shift @array;
print "@array\n";

#颠倒数组元素顺序 reverse 不会改变原数组
my @array_reverse = reverse @array;
print "reverse answer : @array_reverse \n";

#数组排序 sort 不会改变原数组
my @array_sort1 = sort @array; #按照ASCIICode default order,从小到大排序
print "ASCII sort lu: @array_sort1\n";

my @array_sort2 = sort {
    $b cmp $a} @array; #按照ASCII从大到小排序
print "ASCII sort ul: @array_sort2\n";

my @array_sort3 = sort {
    $b <=> $a} (4, 1, 9, 10, 100); #Follow the numbers from largest to smallest
print "num sort ul: @array_sort3\n";

#可以自定义排序规则 sort sub_fun @array;

2. 哈希
   重要规则：1.keys唯一 2.Key-value pairs are arranged out of order in the hash

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

#hash的定义 Both single and double quotes can be used when defining
my %hash = ("red", "1", 'blue', "2", "yellow", "3");
#my %hash = ("red"=> "1", "blue"=> "2", "yellow"=> "3");

#调用hash元素
print "hash element ; $hash{'red'}\n"; #You can only use single quotes, not double quotes

#Add or change key pairs
$hash{
    'red'} = "new1";
print "hash new element : $hash{'red'}\n";

#返回hash的所有keys或者所有values
my @keys = keys %hash;
print "keys of hash : @keys\n";

my @values = values %hash;
print "values of hash : @values\n";

#遍历hash键对
while (my ($k,$v) = each %hash)
{
    
    print "keys-values : $k-$v\n";
}

foreach my $keys (sort {
    $hash{
    $b} cmp $hash{
    $a}} keys %hash)#ASCII 从大到小的keys排序
{
    
    print "keys-values ASCII ul : $keys-$hash{$keys}\n";
}

#判断hash中是否有某个key
print "yes\n" if exists $hash{
    'red'};

流程控制结构

1. boolValues ​​and logical operators

• bool

• 逻辑运算符
  && || !

2. 条件判断
   if…elsif…else
   unless（条件为假时进入）else…
   三目运算符… : …?

3. 循环
   while for foreach each

4. 循环控制

IOand file reading and writing

1. IO操作

print 不自带\n
say 自带\n
printf 格式化输出字符串
sprintf 格式化,不输出

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

printf "%010.2f\n", 3.1415126;
#%010.2f
#0 Sets the character width for padding characters
#10 设置字符宽度为10
#.2 设置显示2位小数
#f 输出浮点型


#输出字符串,字符宽度为10,向右对齐,宽度不足用0补齐,By default padding with spaces
printf "%010s\n", "haha";

2. 读写文件操作
   open函数

open file, "<", $filestring;
while(<>)