Indirect Filehandles + use strict = error

bowei_99 has asked for the wisdom of the Perl Monks concerning the following question:

Hi all, I'm to use indirect filehandles, per Damian Conway's PBP, like so:

    my $FH = "DATA";
    open $FH, "<", $filename     or croak "Cannot open file $filename 
+- $!\n";
[download]

Of course, I have

use strict;

enabled, and would like to leave it that way. But because of that, I'm getting the following error when I run the code:

Can't use string ("DATA") as a symbol ref while "strict refs" in use a
+t parse.pl line 105.
[download]

As you'd expect, line 105 is the open statement in the code above.

I'm using perl 5.8.7, so I know I don't need to have

use Symbol qw( gensym );

(according to PBP, pg. 204, it's only needed for versions less than 5.6). I'd also like to stay with the standard builtin modules, so it rules out using IO::File. Any thoughts?

-- Burvil

Comment on Indirect Filehandles + use strict = error Select or Download Code

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Re: Indirect Filehandles + use strict = error by spiritway (Vicar) on Mar 14, 2006 at 02:08 UTC
I think what you're looking for is something like this: `use strict; use warnings; # and so on... open my $FH, "<", $filename or croak "and so on...\n";` [download] There was no need to assign the string DATA to $FH.	[reply] [d/l]
Re: Indirect Filehandles + use strict = error by TheDamian (Vicar) on Mar 14, 2006 at 10:20 UTC
Hi all, I'm to use indirect filehandles, per Damian Conway's PBP, like so: `my $FH = "DATA"; open $FH, "<", $filename or croak "Cannot open file $ +filename $!\n";` [download] Well, that's not quite how I said to do it in PBP. You missed one important caveat. From the book: Whenever you call `open` with an undefined scalar variable as its first argument, `open` creates an anonymous filehandle (i.e. one that isn’t stored in any symbol table), opens it, and puts a reference to it in the scalar variable you passed. So you can open a file and store the resulting filehandle in a lexical variable, all in one statement, like so: `open my $FILE, '<', $filename or croak "Can't open '$filename': $OS_ERROR";` [download] The `my $FILE` embedded in the `open` statement first declares a new lexical variable in the current scope. That variable is created in an undefined state, so the `open` fills it with a reference to the filehandle it’s just created, as described above. The key point being: Whenever you call `open` with an undefined scalar variable as its first argument... So you were nearly right. You just needed a little bit less code: `my $FH; open $FH, "<", $filename or croak "Cannot open file $filename $!\n";` [download] Damian	[reply] [d/l] [select]
Re: Indirect Filehandles + use strict = error by Tanktalus (Canon) on Mar 14, 2006 at 03:13 UTC
IO::File? Not builtin? Yes it is ... I've been using it as part of core at least since 5.6.0, possibly even 5.005053 (or something like that). That said, `open my $fh, '<', $filename ...` works just fine. Note also that I recommend against upper-case lexicals. It gets confusing.	[reply] [d/l]
Re: Indirect Filehandles + use strict = error by zer (Deacon) on Mar 14, 2006 at 02:29 UTC
another option would be with using typeglobs to pass filehandles... probably not what you are looking for. its a way to send filehandles to and from subroutines	[reply]