There is no BNF, but you can paw your way through the yacc grammar in perly.y in the source distribution if you're particularly brave. The grammar relies on very smart tokenizing code, so be prepared to venture into toke.c as well.
In the words of Chaim Frenkel: "Perl's grammar can not be reduced to BNF. The work of parsing perl is distributed between yacc, the lexer, smoke and mirrors." What are all these $@%&* punctuation signs, and how do I know when to use them?
They are type specifiers, as detailed in perldata:
$ for scalar values (number, string or reference)
@ for arrays
% for hashes (associative arrays)
& for subroutines (aka functions, procedures, methods)
* for all types of that symbol name. In version 4 you used them like
pointers, but in modern perls you can just use references.There are couple of other symbols that you're likely to encounter that aren't
really type specifiers:
<> are used for inputting a record from a filehandle.
\ takes a reference to something.Note that <FILE> is neither the type specifier for files
nor the name of the handle. It is the <> operator applied
to the handle FILE. It reads one line (well, record--see
perlvar/$/) from the handle FILE in scalar context, or all lines
in list context. When performing open, close, or any other operation
besides <> on files, or even when talking about the handle, do
not use the brackets. These are correct: eof(FH), seek(FH, 0,
2) and "copying from STDIN to FILE".