Re^2: How can you check to see if a file handle is already open?

Thanks for the info, but doesn't this still open possibly unnecessary file handles? Maybe I should elaborate, and perhaps ask forgiveness for not being detailed enough.

while(<DATA>) {
    chomp;
    if ($_ =~ m#^(\d+)/(\d+)/(\d+)\s+.*admin2;user) {
        open(FH$3, ">$3.$2.$1");
        print "$_\n" FH$3;
    }
}
[download]

The problem with the above, is FH$3 may already be open, and I don't want to try to reopen it.

And the problem with my first example is that it may open files for which I have no data, for example there was no data on the 15th, but I had opened the file anyway ( resulting in an un-needed 0 length file.

Thanks again, for the help

agent_smith

Comment on Re^2: How can you check to see if a file handle is already open? Download Code

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Re^3: How can you check to see if a file handle is already open? by moritz (Cardinal) on Jan 16, 2008 at 16:46 UTC
I could have made it clearer ;-) You can actually avoid opening all the file handles with a small sub: `my %handles; sub handle_for_name { my $f = shift; if ($handles{$f}){ return $handles{$f}; } else { open my $h, '<', $f or die "Can't open file '$f': $!"; $hanldes{$f} = $h; return $h; } }` [download] And then whenever you need a file handle you just call that function that opens the file if it's not already opened. You can make that sub even smaller with a neat little trick: `use Memoize; memoize("handle_for_name"); sub handle_for_name { my $f = shift; open my $h, '<', $f or die "Can't open file '$f': $!"; return $h; }` [download] That's magic, eh? To answer your original question: if you have a file handle in a lexical variable `$h`, you can use `if ($fh){ print "file opened\n"}`	[reply] [d/l] [select]
Re^3: How can you check to see if a file handle is already open? by alexm (Chaplain) on Jan 16, 2008 at 17:58 UTC
moritz's approach is the same I had in mind, but there's something else that you should care about: if the dataset contains dates for different months and years, you could run out of resources quite easily (i.e. too many open files). In these cases, FileCache is your friend ;-)	[reply]
Re^3: How can you check to see if a file handle is already open? by mifflin (Curate) on Jan 16, 2008 at 19:58 UTC
Why not just use the IO::Handle package? Use the opened method. It will tell you if a file handle is opened and ready. try the following code... `use strict; use warnings; use IO::Handle; open my $fh, '>', 'file' or die $!; test_fh($fh); close $fh or die $!; test_fh($fh); sub test_fh { my ($fh) = @_; if ($fh->opened()) { print "fh is opened and ready\n"; } else { print "fh is closed\n"; } return; }` [download]	[reply] [d/l]
Re^3: How can you check to see if a file handle is already open? by Limbic~Region (Chancellor) on Jan 16, 2008 at 20:02 UTC
agent_smith, You may find Performance Trap - Opening/Closing Files Inside a Loop useful. Cheers - L~R	[reply]
Re^4: How can you check to see if a file handle is already open? by agent_smith (Scribe) on Jan 16, 2008 at 22:16 UTC
Limbic~Region++, That thread was perfect! Thank you for pointing it out. `while(<INPUT>) { chomp $_; if ( $_ =~ m#^(\d+)/(\d+)/(\d+)\s+# ) { my $date = join( '', ( $3, $1, $2) ); if ( ! $file_handles{$date} ) { open($file_handles{$date}, ">>", "$output_dir/$date") +or die "Could not open $date for writing: $!\n"; print { $file_handles{$date} } "$_\n"; } elsif ( defined $file_handles{$date} ) { print { $file_handles{$date} } "$_\n"; } } }` [download] agent_smith	[reply] [d/l]
Re^5: How can you check to see if a file handle is already open? by alexm (Chaplain) on Jan 17, 2008 at 09:01 UTC
This is quite the same technique that chaos_cat suggested before, just a bit more inefficient, since `print { $file_handles{$date} } "$_\n";` [download] can be put outside the conditional opening of the file.	[reply] [d/l]