You can use a regular expression. The /g modifier in a while-loop will match as many times as possible:

#! /usr/bin/perl
use warnings;
use strict;

use Data::Dumper;

while (<DATA>) {
    my %hash;
    while (/([A-Z])([0-9.]+)/g) {
        my ($key, $num) = ($1, $2);
        $hash{$key} = $num;
    }
    print Dumper(\%hash);
}

__DATA__
N260G02X142.05Y649.62I77.33J58.34H2M25
N265M20
N270G45
N275G01X304.78Y608.8C45.91M25
N280M20
N285G46C0
N290G03X324.39Y638.4I-69.58J67.4H2M25
N295M20
N300G45
N305G01X180.04Y592.89C326.5M25
N310X279.77Y586.78C26.5
N315X195.39Y584.57C336.5
N320X228.31Y579.58C355.92
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