Perl - 标量

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标量是单个数据单元。该数据可能是整数、浮点数、字符、字符串、段落或整个网页。

以下是用标量变量的简单示例：

#!/usr/bin/perl

$age = 25;             # An integer assignment
$name = "John Paul";   # A string 
$salary = 1445.50;     # A floating point

print "Age = $age\n";
print "Name = $name\n";
print "Salary = $salary\n";

这将产生以下结果：

Age = 25
Name = John Paul
Salary = 1445.5

数值标量

标量最常见的是数字或字符串。以下示例演示了各种类型数值标量的用法：

#!/usr/bin/perl

$integer = 200;
$negative = -300;
$floating = 200.340;
$bigfloat = -1.2E-23;

# 377 octal, same as 255 decimal
$octal = 0377;

# FF hex, also 255 decimal
$hexa = 0xff;

print "integer = $integer\n";
print "negative = $negative\n";
print "floating = $floating\n";
print "bigfloat = $bigfloat\n";
print "octal = $octal\n";
print "hexa = $hexa\n";

这将产生以下结果：

integer = 200
negative = -300
floating = 200.34
bigfloat = -1.2e-23
octal = 255
hexa = 255

字符串标量

以下示例演示了各种类型字符串标量的用法。请注意单引号字符串和双引号字符串之间的区别：

#!/usr/bin/perl

$var = "This is string scalar!";
$quote = 'I m inside single quote - $var';
$double = "This is inside single quote - $var";

$escape = "This example of escape -\tHello, World!";

print "var = $var\n";
print "quote = $quote\n";
print "double = $double\n";
print "escape = $escape\n";

这将产生以下结果：

var = This is string scalar!
quote = I m inside single quote - $var
double = This is inside single quote - This is string scalar!
escape = This example of escape -       Hello, World

标量运算

您将在单独的章节中看到Perl中可用各种运算符的详细信息，但在这里我们将列出一些数值和字符串运算。

#!/usr/bin/perl

$str = "hello" . "world";       # Concatenates strings.
$num = 5 + 10;                  # adds two numbers.
$mul = 4 * 5;                   # multiplies two numbers.
$mix = $str . $num;             # concatenates string and number.

print "str = $str\n";
print "num = $num\n";
print "mul = $mul\n";
print "mix = $mix\n";

这将产生以下结果：

str = helloworld
num = 15
mul = 20
mix = helloworld15

多行字符串

如果要将多行字符串引入程序中，可以使用标准单引号，如下所示：

#!/usr/bin/perl

$string = 'This is
a multiline
string';

print "$string\n";

这将产生以下结果：

This is
a multiline
string

您也可以使用“here”文档语法来存储或打印多行，如下所示：

#!/usr/bin/perl

print <<EOF;
This is
a multiline
string
EOF

这也会产生相同的结果：

This is
a multiline
string

V-字符串

形式为 v1.20.300.4000 的字面量被解析为由具有指定序号的字符组成的字符串。此形式称为 v-字符串。

v-字符串提供了一种替代且更易读的构造字符串的方法，而不是使用不太易读的插值形式“\x{1}\x{14}\x{12c}\x{fa0}”。

它们是以 v 开头，后跟一个或多个用点分隔的元素的任何字面量。例如：

#!/usr/bin/perl

$smile  = v9786;
$foo    = v102.111.111;
$martin = v77.97.114.116.105.110; 

print "smile = $smile\n";
print "foo = $foo\n";
print "martin = $martin\n";

这也会产生相同的结果：

smile = ☺
foo = foo
martin = Martin
Wide character in print at main.pl line 7.

特殊字面量

到目前为止，您一定对字符串标量及其连接和插值操作有所了解。那么让我告诉您三个特殊字面量 __FILE__、__LINE__ 和 __PACKAGE__ 分别表示程序中该点的当前文件名、行号和包名。

它们只能用作单独的标记，不会被插入到字符串中。查看下面的示例：

#!/usr/bin/perl

print "File name ". __FILE__ . "\n";
print "Line Number " . __LINE__ ."\n";
print "Package " . __PACKAGE__ ."\n";

# they can not be interpolated
print "__FILE__ __LINE__ __PACKAGE__\n";

这将产生以下结果：

File name hello.pl
Line Number 4
Package main
__FILE__ __LINE__ __PACKAGE__