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care to explain __DATA__?

by waxmop (Beadle)
on Feb 24, 2003 at 21:55 UTC ( #238251=note: print w/ replies, xml ) Need Help??


in reply to Re: best way to change xml record using XML::Simple?
in thread best way to change xml record using XML::Simple?

How does the __DATA__ block work? Is that some sort of handle? Any links to explanatory would be much appreciated.


Comment on care to explain __DATA__?
Re: care to explain __DATA__?
by Zaxo (Archbishop) on Feb 24, 2003 at 22:07 UTC

    From perldata:

    The two control characters ^D and ^Z, and the tokens __END__ and __DATA__ may be used to indicate the logical end of the script before the actual end of file. Any following text is ignored.

    Text after __DATA__ but may be read via the filehandle "PACKNAME::DATA", where "PACKNAME" is the package that was current when the __DATA__ token was encountered. The filehandle is left open pointing to the contents after __DATA__. It is the program's responsibility to "close DATA" when it is done reading from it. 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".

    See SelfLoader for more description of __DATA__, and an example of its use. Note that you cannot read from the DATA filehandle in a BEGIN block: the BEGIN block is executed as soon as it is seen (during compilation), at which point the corresponding __DATA__ (or __END__) token has not yet been seen.

    After Compline,
    Zaxo

Re: care to explain __DATA__?
by BrowserUk (Pope) on Feb 24, 2003 at 22:13 UTC

    I can't find a reference to __DATA__ in the docs. I know its there somehere. Maybe someone else will post one.

    Essentially, you can use <DATA> as a file handle that you don't need to open to access anything after the __DATA__ marker at the end of your source file, __END__ works too, but has caveats when used with modules I was informed recently.

    It's very useful for testing and demo purposes. You can even have multiple embedded and even writable files using Damian Conway's Inline::Files, I don't think they would be useful for your purposes here though.


    ..and remember there are a lot of things monks are supposed to be but lazy is not one of them

    Examine what is said, not who speaks.
    1) When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
    2) The only way of discovering the limits of the possible is to venture a little way past them into the impossible
    3) Any sufficiently advanced technology is indistinguishable from magic.
    Arthur C. Clarke.

      perldoc perldata, about halfway down. Also, in the camel on pages 68 and 660.

      --- print map { my ($m)=1<<hex($_)&11?' ':''; $m.=substr('AHJPacehklnorstu',hex($_),1) } split //,'2fde0abe76c36c914586c';

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