Use splice, although, some might not recommend it. I use it extensively, when working with arrays, since, it greatly simplifies and shortens your code. Also, it's very efficient.

Your code:

for my $key (keys %coll_key_hash) {
  foreach my $rec (@recs_read) {
    my @fields = split(/\|/, $rec);
    if ($fields[0] eq '010') {
      if ($fields[3] =~ $key) {
        $print_record = 1;
        if  ($key ne $prev_key) {
          $prev_key = $key;
          print_record ("CUST-BEG|$seq\n",' ');
        }
        print_record ("$rec\n",'c');
      }
      else {
          $print_record = 0;
      }
    }
    else {
      if ($print_record) {
          print_record ("$rec\n",'c');
      }
    }
  }
}
[download]

First, I would like to simplify it, in order to work with it easier:

for my $key (keys %coll_key_hash){
    for my $rec (@recs_read){
        my @fields = split(/\|/, $rec);

        if($fields[0] eq '010'){
            $print_record = 0;
            if($fields[3] =~ $key){ #shouldn't this be /$key/ ?
                $print_record = 1;
                unless($key eq $prev_key){
                    $prev_key = $key;
                    print_record ("CUST-BEG|$seq\n",' ');
                }
            }
        }

        if($print_record){
            print_record ("$rec\n",'c');
        }
    }
}
[download]

The splice algorhythm to delete an array record and to check for loop iteration consistence:

for my $key (keys %coll_key_hash){
    for(my $recIdx = 0; $recIdx < scalar @recs_read; $recIdx++){
        #check, if redo overflowed the end of an array:
        next if(($recIdx + 1) > scalar @rec_read);

        my $rec = $recs_read[$recIdx];
        my @fields = split(/\|/, $rec);

        if($fields[0] eq '010'){
            $print_record = 0;
            if($fields[3] =~ $key){ #shouldn't this be /$key/ ?
                $print_record = 1;
                unless($key eq $prev_key){
                    $prev_key = $key;
                    print_record ("CUST-BEG|$seq\n",' ');
                }
            }
        }

        if($print_record){
            print_record ("$rec\n",'c');
            #Delete one record at the specified index:
            splice(@recs_read, $recIdx, 1);
            #Since the record at the current index is deleted, the new
+ record shifted to the same index, so we test it again:
            redo;
        }
    }
}
[download]

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