can the default file handle be localized?

perl5ever has asked for the wisdom of the Perl Monks concerning the following question:

I would like to "localize" the default file handle so that it is automatically restored when I exit a block. Something like:


  open(my $fh, ...);
  my $OLDFH;
  {
    $OLDFH = select($fh);
    print ...;
    ...
  }
  select($OLDFH);
[download]

except that select($OLDFH) will always get executed when control leaves the inner block (exception, return, etc.)

What's a good way to do this? eval works for catching exceptions. Is there a way to do this with local() ?

Would creating an object whose DESTROY method restores the default handle work?

Comment on can the default file handle be localized? Select or Download Code

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Re: can the default file handle be localized? by ikegami (Patriarch) on Mar 12, 2009 at 21:27 UTC
`use Sub::ScopeFinalizer qw( scope_finalizer ); { my $old_fh = select($fh); my $sentry = scope_finalizer { select($old_fh); }; ... }` [download] Sub::ScopeFinalizer	[reply] [d/l]
Re^2: can the default file handle be localized? by hbm (Hermit) on Mar 12, 2009 at 21:44 UTC
And I was going to link an earlier node of yours: Re: Localized STDIO and system()	[reply]
Re^3: can the default file handle be localized? by ikegami (Patriarch) on Mar 12, 2009 at 21:57 UTC
The OP wants the file handle to be restored automatically on scope exit. ~~The linked node does not provide a means of doing so.~~ In fact, Scope::Finalizer could have been used in that post too. `use Sub::ScopeFinalizer qw( scope_finalizer ); { open(my $old_stdout, '>&', STDOUT) or die; my $sentry = scope_finalizer { close(STDOUT); open(STDOUT, '>&', $old_stdout) or die; }; close(STDOUT); open(STDOUT, '>', $file) or die; ... }` [download] The only reason I didn't is that "..." is a call to `system`, and that doesn't `die` or otherwise exit the block. Update: I missed it since the point of the linked post was to avoid using `local STDOUT` in the circumstances of that thread, but `local STDOUT` is a simpler alternative to using `select` + `scope_finalizer`: `{ local STDOUT = $OLDFH; ... }` [download]	[reply] [d/l] [select]
Re: can the default file handle be localized? by perl5ever (Pilgrim) on Mar 12, 2009 at 22:15 UTC
Ok - the default file handle can't be localized, but the symbol `STDOUT` can be. So if you know the name of the current default file handle then you can do what I want with `local()`. Thanks!	[reply] [d/l] [select]