Perl 简明教程

Perl - Scalars

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

下面是使用标量变量的一个简单示例−

#!/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";

这会产生以下结果 −

Age = 25
Name = John Paul
Salary = 1445.5

Numeric Scalars

标量最常见的是数字或字符串。以下示例演示各种类型的数字标量的用途 −

#!/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";

这会产生以下结果 −

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

String Scalars

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";

这会产生以下结果 −

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

Scalar Operations

您将在单独的章节中看到 Perl 中可用的各种运算符的详细信息，但我们在这里列出一些数字和字符串操作。

#!/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";

这会产生以下结果 −

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

Multiline Strings

如果您想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";

这会产生以下结果 −

This is
a multiline
string

您还可以使用“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-Strings

形式为 v1.20.300.4000 的文本被解析为由指定序数的字符组成的字符串。此形式称为 v 字符串。

与使用不太可读的插形式“\x{1}\x{14}\x{12c}\x{fa0}”相比，v 字符串提供了一种替代的且更具可读性的方式来构造字符串。

它们是从 v 开头的任何文本，后跟一个或多个用点分隔的元素。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.

Special Literals

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。因此，让我告诉你三个特殊的文本 FILE 、 LINE 和 PACKAGE 表示程序中当前的文件名、行号和软件包名称。

它们只能用作单独的标记，并且不会插值到字符串中。查看以下示例 −

#!/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";

这会产生以下结果 −

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