But what I really want to do is substitute $EXEC_block with ...... 'any element of the array: @EXEC_block'.

use Regexp::List ();

$EXEC_block = Regexp::List->new->list2re(@EXEC_block);

...
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Reference: Regexp::List

please explain to me why Perl does not allow !=~.

Reference: perlop

Nice answer, and an informative one. In fact generally one does this by hand joining on "|" - and probably forgetting to \Q...\E (or quotemeta). However it is worth mentioning that the OP may also do like most mortals:

for my $EXEC_block (@EXEC_block) {
    last if s/...//;
    # since we don't want to try again after we succeeded!
}
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PS: shameless self ad - (slightly) related topic!

To answer your second question first (because it is well stated and understandable): it should be !~

Your main question is unclear. Can you post a self contained code fragment that demonstrates the problem you are trying to solve? Do you mean that you want to concatentate a number of strings to generate one big string to match, or do you want the match to succeed if any of a number of strings match (!~ seems unlikely in that case), or do you mean that you wish to select one array element as the match string?

Here's some code illustrating the last case:

use strict;
use warnings;

my $chosen = 'some text';
my @array = (qr'some', qr'more', qr'text');
my $index = 1;

if (defined $chosen && $chosen !~ /$array[$index]/)
  {
  print "\$array[$index] matches\n";
  }
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# @a holds a list of string
my @a = ("a", "b", "c", "/", "\[", "\"");

#create a regex that matches every element in the array
my $re = do { qr/(@{[join ("|", map { quotemeta } @a)]})/ };
die "not a regex!" unless ref($re) eq "Regexp";
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#you don't need to escape ;
... $chosen_C !=~ /^\*.{36};$re;/ ...
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my $re = do { qr/^\*.{36};(@{[join ("|", map { quotemeta } @a)]});/ };
die "not a regex!" unless ref($re) eq "Regexp";

... $chosen_C !=~ $re ...
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