print to a filehandle

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

Does anyone know how to fool perl parser to print to a filehandle that is stored in an array or a hash? For example, this works as expected,

$_ = \*STDOUT;
print $_ "moo\n";
[download]

but this does not even compile:

$_->[0] = \*STDOUT;
print $_->[0] "moo\n";

String found where operator expected at a.pl line 2, near "] "moo\n""
        (Missing operator before  "moo\n"?)
syntax error at a.pl line 2, near "] "moo\n""
Execution of a.pl aborted due to compilation errors.
[download]

ideas? ( and no, please don't suggest $_=$_->[0], it's no fun)

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Re: print to a filehandle by imp (Priest) on Dec 21, 2006 at 13:25 UTC
`$_->[0] = \*STDOUT; print { $_->[0] } "moo\n";` [download]	[reply] [d/l]
Re^2: print to a filehandle by jettero (Monsignor) on Dec 21, 2006 at 13:28 UTC
That syntax never made sense to me. It's correct, but it doesn't feel right. If it's `%h = %{ $h };` and `@a = @{ $a }`, then why isn't it `print { $_->[0] } "moo\n"`? am I going it alone on that? Perhaps I simply dont' understand the context* of the filehandle in a print statement. Hrm, perldsc leads me to believe it's just another code block (rather than a deref) so the parser can figure out it's a file handle argument ... maybe? -Paul	[reply] [d/l] [select]
Re^3: print to a filehandle by polettix (Vicar) on Dec 21, 2006 at 14:22 UTC
AFAIK, it's a parser issue (hence the syntax error) caused by the fact that Perl supports two flavours of `print()`, one with the filehandle and the other without it (in which case it defaults to STDOUT). When perl "sees" `$_->[0]`, it assumes that the latter flavour is in force, and by the time it arrives to `"moo\n"` it's expecting to find an operator (e.g. a comma, or a concatenation dot, or whatever). On the other hand, using the block resolves this ambiguity towards the former `print()` flavour. Flavio perl -ple'$_=reverse' <<<ti.xittelop@oivalf Don't fool yourself.	[reply] [d/l] [select]
Re^3: print to a filehandle by f00li5h (Chaplain) on Dec 21, 2006 at 13:34 UTC
I may have overheard most of a conversation stating that print is actually done as an indirect function call on a bareword (with magic to allow it to work) then again, i could have made it all up... the `prin { $_->[0] } @foo` we're seeing here is a block returning a file handle for print to write to (as perldoc says), so it's not a de-reference as `{ ... }` would suggest Update*: added some actual information `@_=qw; ask f00li5h to appear and remain for a moment of pretend better than a lifetime;;s;;@_[map hex,split'',B204316D8C2A4516DE];;y/05/os/&print;`	[reply] [d/l] [select]
Re^3: print to a filehandle by Fletch (Bishop) on Dec 21, 2006 at 14:17 UTC
Think of them all as blocks returning a value (the block `{ $h }` is returning a hashref, which is then dereferenced by `%`); this particular instance just happens to be un-sigiled because you don't normally need a sigil on the filehandle slot argument anyhow.	[reply] [d/l] [select]
Re^3: print to a filehandle by Anonymous Monk on Dec 21, 2006 at 14:22 UTC
`perldoc -f print`: Note that if you're storing FILEHANDLES in an array or other expression, you will have to use a block returning its value instead: `print { $files[$i] } "stuff\n"; print { $OK ? STDOUT : STDERR } "stuff\n";` [download]	[reply] [d/l]