So, to be able to search for this 2-line string in a document that uses Unix-type line endings:

Reach Holly Smith for help by sending an email
To hollysmith@nosuchdomain.com.

.... the character-specific way to do it (rather than using \n) would have been to store the “old string”~“new string” line in a __DATA__ block, like this, using the Unix-type newline character (code point 10, or 0A in hexadecimal):

__DATA__
Reach Holly Smith for help by sending an email\x{0A}to hollysmith@nosuchdomain.com.~For more information, contact Holly Smith.

...where the preceding line is a single line even though it almost certainly will wrap on this web page; is that what you mean?

I think I’m coming to see the point of being able to use \n in a regular expression — it avoids the need to specify what the characters are that represent a new line in the operating system being used to write and read the file, and it’s a memorable way to avoid having to look up the code point for those characters. Plus a manual entry of a new line at the keyboard while creating a line-by-line data file would gunk up the use of

while ( <DATA> )

Update: davebaker changed this post (without citation!) while I was composing this reply.

---

... a data block or file that contains “old string”~“new string” lines:

__DATA__
... an email\x{0A}to ....~For more information, ....
(Is that what you mean?)

No. (Well, at least that's not the point I would make. :)

The point I would make is that the string you get | read from a __DATA__ or __END__ block or from a regular file is essentially the same as a single-quoted string defined in a script, and such a string can be used directly as a regex search pattern:

Win8 Strawberry 5.8.9.5 (32)  Tue 03/16/2021 17:26:59
C:\@Work\Perl\monks\davebaker
>perl -Mstrict -Mwarnings

my $s = 'foo
bar';
print "A: >>$s<< \n";

my $search  = 'foo\nbar';   # note single quotes!
print "B: >>$search<< \n";  # \n is '\n'

my $replace = "hoo-ray";  # can be single/double quotes

$s =~ s/$search/$replace/;  # no /g - one replacement only
print "C: >>$s<< \n";

^Z
A: >>foo
bar<<
B: >>foo\nbar<<
C: >>hoo-ray<<
[download]

If the search string/pattern is held in a file, the process is similar, except you usually need to chomp the string before you use it:

Win8 Strawberry 5.8.9.5 (32)  Tue 03/16/2021 17:28:26
C:\@Work\Perl\monks\davebaker
>type search.dat
foo\nbar

>perl -Mstrict -Mwarnings

my $s = 'foo
bar';
print "A: >>$s<< \n";

open my $fh, '<', 'search.dat' or die "opening: $!";

chomp(my $search = <$fh>);
print "B: >>$search<< \n";  # \n is essentially '\n'

my $replace = "hoo-ray";

$s =~ s/$search/$replace/;
print "C: >>$s<< \n";

^Z
A: >>foo
bar<<
B: >>foo\nbar<<
C: >>hoo-ray<<
[download]

I think that if you use '\n' (or the equivalent from a file) in a regex search pattern and if you use default I/O for reading all your files, then you will be able to do automatic text editing in an OS-agnostic way, at least across the Windows/*nix iron curtain. The '\n' sequence in a regex is the universal representation of a default newline.

(In general, I think use of qr// is definitely best practice for defining search regexes in a script, not single- or double-quoted strings, but if you're reading from a file, you're kinda stuck with what you've got.)

---

Give a man a fish:  <%-{-{-{-<

I'm not sure I understand your question.

If you want OS sensitive line breaks in DATA you'll need to translate them.

I'd suggest using plain "enter" in the input and

$output = join "\n", <DATA>

In case of OS problems when reading DATA by line, just adjust $/ before. (Never happened to me *)

> Is that what you mean?

I suggested using HERE-docs instead of DATA. They are per default interpolated.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}

update

*) actually, this problem can't arise, because Perl reads DATA like it's own code, its the same filehandle. I.e. the script won't run if there where any problems with OS specific line-endings