here-document without interpolation (<<DELIMITER;)

[gmpassos]

I was looking for a way to use the here-document (<<DELIMITER;) to set some data section in the class.

But this sections need to be exactly as they where declared, soo, if some variable exists there can't be parsed.

Soo, this data:

$data = <<DATAFOO;
bla bla bla $globalvar
DATAFOO

print "$data\n" ;

prints:

bla bla bla

But I need that:

bla bla bla $globalvar

Looking at perldoc I found

## From perldiag:
=item Use of bare << to mean <<"" is deprecated

(D deprecated) You are now encouraged to use the explicitly
quoted form if you wish to use an empty line as the 
terminator of the here-document. 

## From perlop

    Customary  Generic        Meaning         Interpolates
    ''     q{}          Literal          no
    ""    qq{}          Literal          yes
    ``    qx{}          Command          yes*
        qw{}         Word list          no
    //     m{}       Pattern match      yes*
        qr{}          Pattern          yes*
         s{}{}        Substitution      yes*
        tr{}{}      Transliteration      no (but see below)
        <<EOF                 here-doc            yes*

    * unless the delimiter is ''.

Soo, testing some codes I saw that is possible to write that:

$data = <<'DATAFOO';
bla bla bla $globalvar
DATAFOO

print "$data\n" ;

And the output is:

bla bla bla $globalvar

OK, I found what I want. But the use of <<'DELIMITER'; is right/maintained? It works, but I never saw that and is not well documented, or I'm the only one that doesn't know that?

[thelenm]

Yes, you found the correct way to do what you were trying to do. The documentation in perlop may not be particularly clear, but the "*" next to "yes" in the "Interpolates" column is explained as "unless the delimiter is ''". So you can use single quotes to prevent interpolation with qx, m//, qr, s///, and here-docs.

[Roger]

It is well documented in the perlop documentation. Search for '<<EOF'.

[Abigail-II]

The use of single quotes around the delimiter is the correct way of doing this.

Abigail

[Coruscate]

Heredocs allow you to use a single blank line as your end delimeter if you wish. This means that rather than writing

print <<"Done";
foo
bar
baz
Done

print "aha!\n";

, you can write

print <<"";
foo
bar
baz

print "aha!\n";

(note the lack of anything but a blank line between "baz" and the following print statement). It was previously allowed to use

print <<;
foo
bar
baz

print "aha!\n";

(note the plain and simple "print <<;" line). You can still use that simple version, but it's best not to as there is no guarantee that such functionality will be reserved in future perl versions (and that is why the warnings pragma will cough up that deprecated message if you use "print <<;").