Win8 Strawberry 5.8.9.5 (32)  Wed 06/09/2021 15:25:55
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings

use Data::Dump qw(dd);

my $data = <<'EOD';
bist_ctlr_clk_bistctlr,

bist_ctlr_rst_bistctlr_n,

bist_ctlr_serial_in_system,

bist_ctlr_serial_out_system,

bist_ctlr_shift_en_system,

bist_ctlr_global_bbad,

bist_ctlr_global_repairable,

bist_ctlr_bist_mode,

bist_ctlr_mem_type_sel,

bist_ctlr_mode_sel,

bist_ctlr_memsafe,

bist_ctlr_sif_reg_en_system,

bist_ctlr_sif_load_en_system,

bist_ctlr_sif_update_en_system,

bist_ctlr_mem_atpg_mode,

bist_ctlr_flash_data_select,

bist_ctlr_flash_repair_data,

bist_ctlr_bend,
EOD

open (my $ifh51, '<', \$data) or die $!;

my $rx_match = qr{ bist_mode | mode_sel | mem_type_sel }xms;
my @matched;

LINE51:
while (my $line51 = <$ifh51>) {

    # no further processing unless something matches.
    next LINE51 unless $line51 =~ $rx_match;

    # remove rightmost comma.
    $line51 =~ s{ , (?= [^,]* \Z) }{}xms;

    # save what was matched and processed.
    push @matched, $line51;

    }

dd \@matched;

^Z
[
  "bist_ctlr_bist_mode\n",
  "bist_ctlr_mem_type_sel\n",
  "bist_ctlr_mode_sel\n",
]