Here-docs are the exception to this. One can always find a terminator, possibly several characters long, that doesn't appear within the string itself. Thus, backslashes are free to be regular characters in a here-doc.

I don't think you're missing anything; this is just how strings work in Perl.

In any quoted string ("", '', qq{}, q{}, etc.), a double backslash must be interpolated as a single backslash, because a backslash is used to escape the quoting character(s). This makes it possible to get the one character string \ and the two character string \', with '\\\'' and '\\', respectively.

I don't see what's wrong with having '\' mean \ and having '\'."'" or q<\'> mean \'. It's a little more typing, but personally if I was the creator of Perl I would sacrifice the special meaning of backslashes in single-quoted strings for more normality...oh well, I'll have to be content with a source filter or using here-docs. But...

Here-docs are the exception to this. One can always find a terminator, possibly several characters long, that doesn't appear within the string itself. <

This is something I've been thinking about. What if I'm quoting arbitrary user-supplied data in an eval()? I wouldn't want to remove any occurances of the here-doc terminator I was using -- that might upset users whose data contains my terminator. Even if the terminator is a long and rare word, there is still a chance of data/terminator clashing -- disallowing the terminator in the data seems very cargo-cult and wrong to me.

I guess the best here-doc terminator in this case would be a randomly-generated one...if only Perl had a qb// operator to quote an arbitrary number of bytes. (__DATA__ doesn't do what I want, since it is only one section. And if I want multiple sections, I need separators. The same exact problem all over again. Oh wait -- I could just store the number of bytes inside each section of the DATA. But then I have an evil arbitrary limit on how much data the user can supply. Unless I use BER encoded integers. Too much work for me.)

As you suggest, this quoting semantic is really just a design decision.

If you need to quote arbitrary data in a here-doc, you might try something like the following:

my $data = get_some_arbitrary_data();

$data =~ s/^( *)$/ $1/gm;

$eval = "<<'';\n$data\n\n";

$result = eval $eval;
$result =~ s/^ //;

print $result;
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If you specify an empty terminator, then the here-doc ends at the next empty line. Just make sure there are no empty lines in the arbitrary data; perhaps by prepending a space to every empty line. I added a space to every line consisting only of spaces, so I could convert the data back after the eval.