It's not necessary.

>perl -e"$_='a'; print qr/$_{3}/"
(?-xism:a{3})
[download]

And beyond being unnecessary, it will never help either. If you were to do ${_}{...} to prevent $_{...} from beint treated as a hash element, it still wouldn't do what you want. See Re: Of scalars, hashes, quantifiers, and regexen.

So when I run:

use strict;
use warnings;

my ($ikegamiRe1) = map qr/$_/, join '|', map "(?<=$_{3})$_+", map quot
+emeta,
    1 .. 9;
[download]

I should ignore:

Use of uninitialized value in concatenation (.) or string at noname.pl
+ line 4.
Use of uninitialized value in concatenation (.) or string at noname.pl
+ line 4.
Use of uninitialized value in concatenation (.) or string at noname.pl
+ line 4.
Use of uninitialized value in concatenation (.) or string at noname.pl
+ line 4.
Use of uninitialized value in concatenation (.) or string at noname.pl
+ line 4.
Use of uninitialized value in concatenation (.) or string at noname.pl
+ line 4.
Use of uninitialized value in concatenation (.) or string at noname.pl
+ line 4.
Use of uninitialized value in concatenation (.) or string at noname.pl
+ line 4.
Use of uninitialized value in concatenation (.) or string at noname.pl
+ line 4.
[download]

Update: Oh, and here's an interesting result:

use strict;
#use warnings;

my $str = join '|', map "(?<=${_}{3})$_+", 1 .. 2;
print $str, "\n";
$str = join '|', map "(?<=$_{3})$_+", 1 .. 2;
print $str;
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Prints:

(?<=1{3})1+|(?<=2{3})2+
(?<=)1+|(?<=)2+
[download]

---

Perl reduces RSI - it saves typing

Oh shoot, that's a string literal and not a regexp literal! Fixed.