I was also confused about what this $$blk_ref was about. And I just punted that issue in my direct post. It would be helpful if the OP showed more of his application. Dereferencing a ref to a single scalar is a relatively rare thing in Perl. That is because Perl array iterator operations are very good at hiding this nastiness.

For fun, I used your example data and coded the loop a couple of different ways. Neither of which use an explicit dereferencing operation.

use strict;
use warnings;
use Data::Dump qw(dd);

my @strings = (
   'SMS,SMS1,20190811',
   'SMS,SMSh,20190811',
   'SMS,SMSH,20190811',
   'SMS,SMSx,20190811',
   'SMS,SMSi,20190811',
   'SMS,SMSX,20190811',
   'SMS,SMSI,20190811',
   );

# map{} is a logical thought for an array transformation
#
# Could assign back to @strings or can make 
#   a new array, @strings2
# Could use an "if" and concatenate a message if true
#   and return $_ in any event. Ternary operator here
#   gives a place to put a single token that is 
#   not "SMSblk"

my @strings2 = map{/SMS[1HI]/i ? "$_ is SMSblk":$_}@strings;  
 
dd \@strings2;

=prints:
[
  "SMS,SMS1,20190811 is SMSblk",
  "SMS,SMSh,20190811 is SMSblk",
  "SMS,SMSH,20190811 is SMSblk",
  "SMS,SMSx,20190811",
  "SMS,SMSi,20190811 is SMSblk",
  "SMS,SMSX,20190811",
  "SMS,SMSI,20190811 is SMSblk",
]
=cut

# Or with a for loop instead of map{} 
#   to modify original array:
# Foreach creates an alias and modifying that
#   alias modifies the original array
# No tricky dereferencing is needed.

foreach (@strings)
{
   $_ .= " is SMSblk" if /SMS[1HI]/i;
}

dd \@strings;

=prints:
[
  "SMS,SMS1,20190811 is SMSblk",
  "SMS,SMSh,20190811 is SMSblk",
  "SMS,SMSH,20190811 is SMSblk",
  "SMS,SMSx,20190811",
  "SMS,SMSi,20190811 is SMSblk",
  "SMS,SMSX,20190811",
  "SMS,SMSI,20190811 is SMSblk",
]
=cut
[download]

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.