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Perl - Scalars 介绍

Scalars是数据的单个单位。该数据可能是整数,浮点数,字符,字符串,段落或整个网页。

这是一个使用标量变量的简单Example-

#!/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";

这将产生以下输出-

Age = 25
Name = John Paul
Salary = 1445.5

数字Scalars

标量通常是数字或字符串。以下Example演示了各种类型的数字标量的用法-

#!/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";

这将产生以下输出-

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

字符串Scalars

以下Example演示了各种类型的字符串标量的用法。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";

这将产生以下输出-

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运算

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,但是在这里,我们将列出一些数字和字符串运算。

#!/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";

这将产生以下输出-

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

多行字符串

如果要在程序中引入多行字符串,可以使用以下标准单引号-

#!/usr/bin/perl

$string = 'This is
a multiline
string';

print "$string\n";

这将产生以下输出-

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

这也会产生相同的输出-

This is
a multiline
string

V-Strings

v1.20.300.4000形式的文字被解析为由具有指定序数的字符组成的字符串。这种形式称为v-strings。

v字符串提供了一种替代的且更易读的方式来构造字符串,而不是使用可读性较差的内插形式" \x {1} \x {14} \x {12c} \x {fa0}"。

它们是任何以v开头且后接一个或多个点分隔元素的文字。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";

这也会产生相同的输出-

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

特殊文字

到目前为止,您必须对字符串标量及其串联和插值运算有一定的了解。因此,让我告诉您三个特殊的文字__FILE__,__LINE__和__PACKAGE__代表程序中该点的当前文件名,行号和程序包名称。

它们只能用作单独的标记,而不会内插到字符串中。检查以下Example-

#!/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";

这将产生以下输出-

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