Perl |变量范围
变量的作用域是程序中可访问变量的部分。范围也称为程序中变量的可见性。在 Perl 中，我们可以声明全局变量或者私有变量。私有变量也被称为词汇变量。
全局变量的范围
全局变量可以在程序中创建的任何函数或块中使用。它在整个程序中是可见的。全局变量可以直接使用，并且可以从程序的每个部分访问。
示例 1: 变量 $name 在代码的开头声明。它在文件的末尾随处可见。即使在街区内。即使那些在函数声明中。如果我们改变块内的变量，将会改变代码其余部分的值。即使在街区外。
# Perl program to illustrate the
# Scope of Global variables
# declaration of global variable
$name = "GFG";
# printing global variable
print "$name\n";
# global variable can be used
# inside a block, hence the we
# are taking a block in which
# we will print the value of
# $name i.e. global variable
{
# here GFG will print
print "$name\n";
# values in global variable can be
# changed even within a block,
# hence the value of $name is
# now changed to "GeeksforGeeks"
$name = "GeeksforGeeks";
# print function prints
# "GeeksforGeeks"
print "$name\n";
}
# changes made inside the above block'
# are reflected in the whole program
# so here GeeksforGeeks will print
print "$name\n";
Output:
GFG
GFG
GeeksforGeeks
GeeksforGeeks
例 2:
# Perl program to illustrate the
# Scope of Global variables
# declaration of global variables
$name = "GFG";
$count = 1;
# printing global variables
print $count." ".$name."\n";
$count++;
# Block starting
{
# global variable can be used inside
# a block, so below statement will
# print GFG and 1
print $count." ".$name."\n";
# incrementing the value of
# count inside the block
$count++;
}
# taking a function
sub func {
# Global variable, $count and $name,
# are accessible within function
print $count." ".$name."\n";
}
# calling the function
func();
Output:
1 GFG
2 GFG
3 GFG
词汇变量的范围(私有变量)
Perl 中的私有变量是在变量前使用 my 关键字定义的。我的关键字将变量限制在声明它的函数或块中。块可以是 for 循环、while 循环，也可以是一个带有大括号的代码块。局部变量的作用域是局部的，它存在于两个大括号(代码块)之间，在代码块之外，这个变量不存在。这些变量也被称为词汇变量。
注意:当在函数或块中使用私有变量时，它们会隐藏以相同名称创建的全局变量。当我们调用带有私有变量的子例程时，它可以在该函数中使用。子程序一退出，私有变量就不能再使用了。
示例:
# Perl program to illustrate the
# scope of private variables
# declaration of global variable
$name = "Global";
$count = 1;
# printing global variables
print $count." ".$name."\n";
# incrementing the value of count
# i.e it become 2
$count++;
# block starting
{
# declaring private variable by using my
# keyword which can only be used
# within this block
my $new_name = "Private";
# global variables are
# accessible inside block
print $count." ".$name."\n";
# incrementing the value
# of global variable
# here it become 3
$count++;
print $name." and ".$new_name."\n";
}
# $new_name variable cannot
# be used outside, hence nothing
# is going to print
print "Variable defined in above block: ".$new_name."\n";
# declaring function
sub func {
# this private variable declaration
# hides the global variable which define
# in the beginning of program
my $name = "Hide";
print $count." ".$name."\n";
}
# calling the function
func();
Output:
1 Global
2 Global
Global and Private
Variable defined in above block:
3 Hide
包变量
在 Perl 中，我们还有一种类型的作用域，叫做包作用域。当我们需要创建可以在不同名称空间中独占使用的变量时，就会用到它。“ main ”是每个 Perl 程序中的默认命名空间。Perl 中的名称空间是使用包关键字定义的。
示例:
# Perl program to illustrate
# the Package Variables
# variable declared in
# main namespace
$var1 = "Main Namespace";
print "Value of Var1: ".$var1."\n";
# package declaration
# Pack1 is the package
package Pack1;
# since $var1 belongs to main namespace,
# so nothing will print inside Pack1
# namespace
print "Value of var1: ".$var1."\n";
# variable declared in Pack1 namespace
# having same name as main namespace
$var1 = "Pack1 Namespace";
# here $var1 belongs to Pack1 namespace
print "Value of var1: ".$var1."\n";
# in-order to print variables
# from both namespace, use
# following method
print "Value of var1: ".$main::var1."\n";
print "Value of var1: ".$Pack1::var1."\n";
Output:
Value of Var1: Main Namespace
Value of var1:
Value of var1: Pack1 Namespace
Value of var1: Main Namespace
Value of var1: Pack1 Namespace
Perl 中的 Our 关键字:“Our”关键字只创建同名的现有包变量的别名。我们的关键字允许使用包变量，而不用用包名限定它，但是只能在“我们的声明的词法范围内。用声明的变量我们的关键字声明了一个包变量的别名，该变量将在其整个词法范围内可见，甚至跨越包边界。
# Perl program to illustrate the use
# of our keyword
# Pack1 namespace declared
# by using the package keyword
package Pack1;
# declaring $Pack1::first_name
# for rest of lexical scope
our $first_name;
$first_name = "Shashank";
# declaring $Pack1::second_name for
# only this namespace
$second_name;
$second_name = "Sharma";
# Pack2 namespace declared
package Pack2;
# prints value of $first_name, as it
# refers to $Pack1::first_name
print "first_name = ".$first_name."\n";
# It will print nothing as $second_name
# does not exist in Pack2 package scope
print "second_name = ".$second_name."\n";
Output:
first_name = Shashank
second_name =
