confusion with my variable in perl

Question

If using use strict and use warning and if I specify my datatype, it works; if I do not specify the my it says error.

use strict;
use warnings;
my $test=10;
my @arr=(10,20,30);

If I declare the array variable name as a number:

 use strict;
 use warnings;
 my @100=(10,20,30);

then when I run that program it says error:

 Can't use global @100 in "my" at number_sclar.pl line 28, near "my @100"

If I remove that my and run that program, it runs without an error.

So please can anyone tell me why my variable is not supported with a numeric array variable name?

Answer 1

From perldoc perlvar:

Perl identifiers that begin with digits, control characters, or punctuation characters are exempt from the effects of the "package" declaration and are always forced to be in package "main"; they are also exempt from "strict 'vars'" errors. A few other names are also exempt in these ways...

Answer 2

As an unintentional side-effect of creating $1, $2, $3, $100, etc (to hold the results of regex captures); @1, @2, @3, @100, etc also get created.

However, the name of these and most of the special vars in perlvar aren't legal names except for package vars. For example, you can't do my $(; or sub (; even though though $( is a valid name for a package variable^[1].

When lexicals were added to Perl in 5.6, it was surely deemed to be to confusing to allow such names for user variables. In fact, I doubt anyone even entertained the thought.

Sigil aside, lexical vars must start with a character in [a-zA-Z_]^[2] and can be followed by a number of characters in [a-zA-Z0-9_]^[2]. As such, @100 is not a valid name for a lexical variable.

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Notes:

1. >perl -e"our $(;"
   
   >perl -e"my $(;"
   Can't use global $( in "my" at -e line 1, near "my $("
   Execution of -e aborted due to compilation errors.
   
   >perl -e"sub (;"
   Prototype not terminated at -e line 1.
   

2. More code points are actually allowed, but they fall outside of ASCII's character set. For simplicity, I only listed the code points that fall inside of ASCII's character set.