__FILE__ = represent the current filename
__LINE__ = line number
__PACKAGE__ package name
If there is no current package (due to an empty package; directive),
__PACKAGE__ is the undefined value.
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__ 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 top level 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