Opening files in 5.004 and 5.8

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

Brethern

I have existing code, much of it going back to Perl 4.?. I now need to run both on systems running 5.004_04 and 5.8. Existing code (which didn't use strict) used a string for a file handle.

sub printSumpn{
  local($handle, file) = ('RPT', '/tmp/report.txt');
  myOpen($handle, $file);
  print $handle "hello world\n";
  close($handle)}

sub myOpen{
  local($handle, $file) =@_;
  # ...do some logging and sanity checking...
  open($handle, ">$file")}
[download]

Coming up to 5.8, this gave various scoldings when I use strict;. Changing 'local' to 'my' and 'RPT' to *RPT seemed to fix the problem.

But under 5.004_04, setting

 my $handle = *RPT;
[download]

leaves $handle undef, so it loses when it does the open (or the print).

I want to set $handle equal to a filehandle, and be able to pass $handle to a file-opening subroutine, to print, and to close. I want to do this in a way that doesn't violate strict. And in a way that works under both 5.004_04 and 5.8.

Can I do that?

thanks
throop

Comment on Opening files in 5.004 and 5.8 Select or Download Code

Replies are listed 'Best First'.
Re: Opening files in 5.004 and 5.8 by gaal (Parson) on May 11, 2007 at 21:27 UTC
Lexical filehandles were introduced in 5.6, IIRC. You can say `my $handle = \*RPT;` [download] and pass it to a subroutine in versions prior to that, though. `close` and friends work with that.	[reply] [d/l] [select]
Re: Opening files in 5.004 and 5.8 by grinder (Bishop) on May 12, 2007 at 15:24 UTC
To minimise the amount of code you have to change, I would just conditionally bring in the Symbol module, and call `gensym` to initialise your file handle, and ditch the 'RPT' stuff. `use Symbol; sub printSumpn{ my($handle, $file) = (gensym(), '/tmp/report.txt');` [download] And everything will work just fine. You don't actually care about what the handle itself looks like, just that it uniquely identifies whatever it's printing to. `gensym` does that for you. • another intruder with the mooring in the heart of the Perl	[reply] [d/l]
Re^2: Opening files in 5.004 and 5.8 by educated_foo (Vicar) on May 12, 2007 at 17:35 UTC
Ugh, another module for the "CPAN one-liners" file: `sub gensym { \*{'__GEN__' . ++$__GEN__::__counter__} }` [download] It's a useful function, but not worth an extra dependency.	[reply] [d/l]
Re^3: Opening files in 5.004 and 5.8 by gaal (Parson) on May 12, 2007 at 18:48 UTC
FWIW, Symbol has been core since 5.002. Also see the comment on copying the glob vs. making a reference in the Symbol.pm implementation.	[reply]


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