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my @array = qw(1 2 3);
@array = qw(one two three) if $op eq 'alpha';

my @xxx;
@xxx = qw(one two three) if $op eq 'numbers';
@xxx = qw(four five) if $op eq 'alpha';
@xxx = qw(six ten) if $op eq 'alp';

#!/usr/bin/perl -w
use strict;
...
    my $greeting = shift;
    print "goodbye $greeting\n";
}