opendir(INDIR, $outdir) or die ("$indir not found\n");
        while (my $infile = readdir(INDIR)) {
                chomp;
                next if $infile !~ /postpaid/;

                #change & to space for sorting purpose
                qx(cat $outdir/$infile |sed 's/\&/\t/g' > $outdir/$infile.tmp);

                #sort the data based on date or second colum
                qx(cat $outdir/$infile.tmp |sort -2 > $outdir/$infile.srt);

                #change back the space to &
                #NOTE: This one not working
                qx(cat $outdir/$infile.srt |sed 's/\t/\&/g' > $outdir/$infile.ok);

                #remove temporary file
                qx(rm -f $outdir/$infile.tmp);
        }
        closedir(INDIR);