How can I use macros in Perl?

How do I use macros in Perl, like I d开发者_Python百科o in C?

Example:

#define value 100 
print value; 

I want to get the output as 100.

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If you just want to define constants (like your example) rather than full macros, there are a couple of perl ways to do this.

Some people like:

use constant value => 100;
print value;

Note that 'value' is a subroutine, not a 'variable'. This means you cannot interpolate it in strings so you have to do. print "The value is ".value."\n";.

The "Best Practices" crowd like:

use Readonly;
Readonly my $value => 100;
print $value;

However, unlike constant, Readonly is not part of the core perl distribution and so needs to be installed from CPAN.

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Perl is not C. You would be much better served by learning the corresponding Perl idioms (such as the already mentioned use constant value => 100) than by trying to drag C idioms into Perl.

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For constants, the common way is to use a constant subroutine that will get inlined by the compiler:

use constant value => 100;

or

sub value () {100}

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Try the following:

macro.pl

    use strict;
    use warnings;
    #define a 10;
    print a;

And run this code using -P switch.

Example: perl -P macro.pl

And use the module Filter::cpp also.