Perl6: Capturing newline in a string

stevieb has asked for the wisdom of the Perl Monks concerning the following question:

Disclaimer: cross-posted at StackOverflow.

In Perl5, I can quickly and easily print out the hex representation of the \r\n Windows-style line ending:

perl -nE '/([\r\n]{1,2})/; print(unpack("H*",$1))' in.txt
0d0a
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update:To create a Windows-ending file on Unix, create a in.txt file with a single line and line ending. Then: perl -ni -e 's/\n/\r\n/g;print' in.txt. (or in vi/vim, create the file and just do :set ff=dos) /update

I have tried many things in Perl6 to do the same thing, but I can't get it to work no matter what I do. Here's my most recent test:

use v6;
use experimental :pack;

my $fn = 'in.txt';

my $fh = open $fn, chomp => False; # I've also tried :bin
for $fh.lines -> $line {
    if $line ~~ /(<[\r\n]>**1..2)/ {
        $0.Str.encode('UTF-8').unpack("H*").say;
    }
}
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Outputs 0a, as do:

/(\n)/
/(\v)/
[download]

First, I don't even know if I'm using unpack() properly. Second, how do I capture both elements (\r\n) of the newline in P6?

Comment on Perl6: Capturing newline in a string Select or Download Code

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Re: Perl6: Capturing newline in a string by Laurent_R (Canon) on May 31, 2016 at 07:30 UTC
Hm, not sure to fully understand what you are trying to do, but please note that the Perl 6 `.lines` method strips the newline characters. Under Unix: `$ perl6 -e 'lines("a\nb").perl;' ("a", "b").Seq` [download] Under Windows: `C:\Users\Laurent>perl6 -e "dd qq{a\nb\r\nc}.lines;" ("a", "b", "c").Seq` [download]	[reply] [d/l] [select]
Re^2: Perl6: Capturing newline in a string by stevieb (Canon) on May 31, 2016 at 13:45 UTC
Here's an example of what I'm trying to do: open a Unix file on Windows (or vise-versa) read in the file contents regardless of line-endings (works with `lines`) write back to the file (either write or append), using the SAME line endings that were originally found in the file, as opposed to clobbering the file with the wrong endings For instance, if I start with a Unix file with one line and a unixy `\n` on a Windows system, then append to the file, I get one line with a nix ending, and one with a windows ending: `10 10^M` [download] This kind of thing happens in both P5 and P6. I wrote a module that handles this in Perl 5, File::Edit::Portable. To learn about Perl6, I thought I'd port this module over, but the most fundamental aspect of figuring out what style of endings a file has seems to be a bit difficult in Perl6 :) Perhaps I should have stated what X was instead of asking about Y (XY Problem) :)	[reply] [d/l] [select]
Re^3: Perl6: Capturing newline in a string by raiph (Deacon) on May 31, 2016 at 16:51 UTC
I just noticed your SO has some answers. Perhaps those give you the info you need and what follows is redundant but maybe not, and I'd already written this, so: Read Sinan Unar's Christmas blog about newline handling for a wrap up of the last round of changes in Perl 6 handling of newlines. If that doesn't provide all the answers you need, consider digging deeper (in particular, search for 'newline' in jnthn's blog posts about NFG to understand some key constraints on how Perl 6 must handle newlines due to NFG (due to Unicode), and/or maybe skim the #perl6 daily logs that mention both user nanis (Sinan) and newlines) and/or visiting the #perl6 or #perl6-dev freenode IRC channels. ETA: This bit from Sinan's post: We don't do any such translation when using .encode/.decode, and of course when reading/writing Bufs to files, providing an escape hatch from translation if needed. reads to me like a very direct claim that there's a way to read and write files without translating newlines. Hth. perl6.party (not mine)	[reply]
Re^3: Perl6: Capturing newline in a string by msh210 (Monk) on May 31, 2016 at 16:31 UTC
Unrelated to your original query, but your module doesn't do quite what it says on the tin. You may wish to emend the documentation. `lines` : `foo<LF>bar<CR><LF>baz` `$ perl -e'use File::Edit::Portable;$r=File::Edit::Portable->new;$h=$r->read("lines");$t=$r->tempfile;print$t $_ while<$h>;$r->write(contents=>$t)'` According to spec, `lines` should be the same after I ran that as before. In fact it was `foo<LF>bar<LF>baz<LF>` afterward.	[reply] [d/l] [select]
Re^4: Perl6: Capturing newline in a string by stevieb (Canon) on May 31, 2016 at 16:41 UTC
Re^3: Perl6: Capturing newline in a string by Laurent_R (Canon) on May 31, 2016 at 16:00 UTC
That's a nice way to learn about Perl 6. :-) I'll take a look at your module and see if I can have an idea which may help you. Update: fixed a typo.	[reply]
Re^4: Perl6: Capturing newline in a string by stevieb (Canon) on May 31, 2016 at 16:43 UTC
Re^5: Perl6: Capturing newline in a string by Laurent_R (Canon) on May 31, 2016 at 22:19 UTC
Some notes below your chosen depth have not been shown here
Re: Perl6: Capturing newline in a string by johngg (Canon) on May 30, 2016 at 23:14 UTC
I haven't had a play with Perl 6 yet so can't help there. There is another way to create a Windows-ending file though. `$ perl -Mstrict -Mwarnings -E ' open my $outFH, q{>:crlf}, \ my $outFile or die $!; say $outFH q{Hi}; close $outFH or die $!; say sprintf q{%02x}, ord for split m{}, $outFile;' 48 69 0d 0a $` [download] Update: The code above was run on Linux Mint 17 with the perl 5.18.2 interpreter. Cheers, JohnGG	[reply] [d/l]