#!/usr/bin/perl

use strict;
use utf8;
binmode STDIN, ":utf8";
binmode STDOUT, ":utf8";

my $str = "See on üks täppidega lause!"; # sample string, want to get rid of spaces and exclamation mark, all other are alphas, and i really need them

# first printout ( how [[:alpha:]] works)
foreach my $mrk ( split(//, $str) ) {
        if ($mrk =~ /^[[:alpha:]]$/ ) {
                print "$mrk";
        }
}
print "\n\n";
# end of first printout


# second printout  ( how [[:alpha:]] doesn't works)
$str =~ s/[[:^alpha:]]//ig;
print "$str\n";
# end of second printout

exit(0);

__END__

First output:
Seeonükstäppidegalause

Second should be also same, but is:
Seeonkstppidegalause