use strict;
use diagnostics;
use warnings;

@ARGV = glob 'file_*';

my $outfile = 'outfile.csv';

open my $OUTFILE, '>', $outfile or die "Cannot open '$outfile' $!";

while ( <> ) {
    if ( eof && !eof() ) {
        <>;<>;
        }
    print $OUTFILE $_;
    }

close $OUTFILE;