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

Somehow I ran into an equivalent of the following, for the script: 
use strict;

while(my $a=<DATA>){
  print $a;
}

__END__
1
2
3
__DATA__
a
b
c

[download]
I was expecting the result to be: 
a
b
c

[download]
But I actually got: 
1
2
3
__DATA__
a
b
c

[download]
So __END__ is equivalent to __DATA__? eveything after __END__ or __DATA__ can be accessed via <DATA>?

Replies are listed 'Best First'.
Re: __END__ is equivalent to __DATA__ ?
by Zaxo (Archbishop) on Dec 07, 2004 at 23:22 UTC

    Almost, but not quite equivalent. The data following __END__ is always associated with namespace main::, while __DATA__ is file scoped. That will matter for data sections occuring in modules.

    A data section may also be started with Ctrl-Z (ascii \x1a).

    You can get the effect your intuition wants with the Inline::Files module. It enables more than one labelled section of data at the end of a perl source file.

    After Compline,
    Zaxo

[reply]
Re: __END__ is equivalent to __DATA__ ?
by mifflin (Curate) on Dec 07, 2004 at 23:11 UTC
    The perl Cookbook recipe 7.6 says they are the same...

    <snippet from the book>

    __DATA__ and __END__ indicate the logical end of a module or script before the physical end of the file is reached. Text after __DATA__ or __END__ can be read through the per-package DATA filehandle. For example, take the hypothetical module Primes. Text after __DATA__ in Primes.pm can be read from the Primes::DATA filehandle.

    __END__ behaves as a synonym for __DATA in the main package. Text after__END__ tokens in modules is inaccessable.

[reply]
      Text after __DATA__ in Primes.pm can be read from the Primes::DATA filehandle.
      Ahh, too bad I didn't get to review that book... I could have marked that sentence as a technical error. As perldata clearly states: 
             Text after __DATA__ but may be read via the filehandle "PACK-
       NAME::DATA", where "PACKNAME" is the package that was current w
+hen the
       __DATA__ token was encountered.

      [download]
      So, what matters is not the name of the file, but rather the "current package" at the point just before the __DATA__ token. I'm surprised Nat and Tom made such a straightforward mistake. (I've just submitted this as an errata for the book, so hopefully future books will get it right.)

      -- Randal L. Schwartz, Perl hacker
      Be sure to read my standard disclaimer if this is a reply.

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Re: __END__ is equivalent to __DATA__ ?
by ccn (Vicar) on Dec 07, 2004 at 23:22 UTC

    see perldata for Special Literals

    For compatibility with older scripts written before __DATA__ was introduced, __END__ behaves like __DATA__ in the toplevel script (but not in files loaded with require or do) and leaves the remaining contents of the file accessible via main::DATA.
[reply]
Re: __END__ is equivalent to __DATA__ ?
by johnnywang (Priest) on Dec 08, 2004 at 18:28 UTC
    Thank you all, I did some test to confirm all your points. Here are the scripts to document this: 
    use strict;
use foo;

print "From <DATA>:\n";
print <DATA>;

print "From <foo::DATA>:\n";
print  <foo::DATA>;

print "From <bar::DATA>:\n";
print <bar::DATA>;


__DATA__
a
b
c

    [download]
    Here's the foo.pm: 
    package foo;
use strict;

package bar;

1;
__DATA__
1
2
3
4

    [download]
    Running the first script gives: 
    From <DATA>:
a
b
c
From <foo::DATA>:
From <bar::DATA>:
1
2
3
4

    [download]
[reply]
[d/l]
[select]

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