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I keep seeing the "my" keyword in front of variable names in example Perl scripts online but I have no idea what it means. I tried reading the manual pages and other sites online but I'm having difficulty discerning what it is for given the difference between how I see it used and the manual.
For example, its used to get the length of the array in this post: Find size of an array in Perl
But the manual says:
A my declares the listed variables to be local (lexically) to the enclosing block, file, or eval. If more than one value is listed, the list must be placed in parentheses.
What does it do and how is it used?
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There is a strange scalar variable called $_ in Perl, which is the default variable, or in other words the topic. In Perl, several functions and operators use this variable as a default, in case no parameter is explicitly used. In general, I'd say you should NOT see $_ in real code.
The short answer is that my marks a variable as private in a lexical scope, and local marks a variable as private in a dynamic scope.
In Perl, the terms function, subroutine, and method are the same but in some programming languages, these are considered different. The word subroutines is used most in Perl programming because it is created using keyword sub.
@ is used for an array. In a subroutine or when you call a function in Perl, you may pass the parameter list. In that case, @_ is can be used to pass the parameter list to the function: sub Average{ # Get total number of arguments passed. $ n = scalar(@_); $sum = 0; foreach $item (@_){ # foreach is like for loop...
my restricts the scope of a variable. The scope of a variable is where it can be seen. Reducing a variable's scope to where the variable is needed is a fundamental aspect of good programming. It makes the code more readable and less error-prone, and results in a slew of derived benefits.
If you don't declare a variable using my, a global variable will be created instead. This is to be avoided. Using use strict; tells Perl you want to be prevented from implicitly creating global variables, which is why you should always use use strict; (and use warnings;) in your programs.
Related reading: Why use use strict; and use warnings;?
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Quick summary: my creates a new variable, local temporarily amends the value of a variable
In the example below, $::a refers to $a in the 'global' namespace.
$a = 3.14159; { my $a = 3; print "In block, \$a = $a\n"; print "In block, \$::a = $::a\n"; } print "Outside block, \$a = $a\n"; print "Outside block, \$::a = $::a\n"; # This outputs In block, $a = 3 In block, $::a = 3.14159 Outside block, $a = 3.14159 Outside block, $::a = 3.14159 ie, local temporarily changes the value of the variable, but only within the scope it exists in.
Source: http://www.perlmonks.org/?node_id=94007
Update
About difference between our and my please see
(Thanks to ThisSuitIsBlackNot).
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