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my $working_dir = $ARGV[0];     # starting directory
my $extension   = $ARGV[1];     # extension to save
...
#       unlink $_              if scalar @matches > 1 && $ext ne $exte
+nsion;
    }
}

my @data;
while (<>) {
...
        }
        print "\n";
}

use POSIX ":sys_wait_h";

...
     sleep(1);  # wait for all children to finish
}
exit 0;

# Straight forward way (sort keys slows down the larger the list)
my %hash = map { $_ => 1 } @items;
...
# This is the method under the hood in List::MoreUtils::uniq
my %h;
my @uniq = map { $h{$_}++ == 0 ? $_ : () } @items;

# AC_CHECK_PM
#----------------------------------------------------------
...
        AC_MSG_ERROR([missing perl module $1, not in @INC])
fi;dnl
])