Programming Perl, 4th Edition

Other Literal Tokens

You should consider any identifier that both begins and ends with a double underscore to be reserved for special syntactic use by Perl. Two such special literals are _ _LINE_ _ and _ _FILE_ _, which represent the current line number and filename at that point in your program. They may only be used as separate tokens; they will not be interpolated into strings. Likewise, _ _PACKAGE_ _ is the name of the package the current code is being compiled into. The token _ _END_ _ (or, alternatively, a Control-D or Control-Z character) may be used to indicate the logical end of the script before the real end-of-file. Any following text is ignored but may be read via the DATA filehandle.

The _ _DATA_ _ token functions similarly to the _ _END_ _ token, but it opens the DATA filehandle within the current package’s namespace, so files you require can each have their own DATA filehandles open simultaneously. For more information, see DATA in Chapter 25.