Readonly my $REGEXP_READONLY => '999986';
  if( $l_line =~ m/$REGEXP_READONLY/ ) {
    # 5.78s - CORE:regcomp
    # 0.91s - CORE:match
    # 1.83s - Readonly::Scalar::FETCH

use constant REGEXP_CONSTANT => '999986';
  if( $l_line =~ m/${\REGEXP_CONSTANT}/ ) {
    # 0.74s - CORE:regcomp
    # 0.75s - CORE:match

  if( $l_line =~ m/999986/ ) {
    # 0.84s - CORE:match

  if( $l_line =~ m/$REGEXP_READONLY/o ) {
    # 0.73s - CORE:regcomp
    # 0.75s - CORE:match

my $l_search_r = qr/$REGEXP_READONLY/;
  if( $l_line =~ $l_search_r ) {
    # 1.33s - CORE:regcomp
    # 0.78s - CORE:match

my $l_search = $REGEXP_READONLY;
  if( $l_line =~ m/$l_search/ ) {
    # 0.74s - CORE:regcomp
    # 0.76s - CORE:match

$l_search = $REGEXP_READONLY;
  if( $l_line =~ m/$l_search/o ) {
    # 0.69s - CORE:regcomp
    # 0.76s - CORE:match