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How can I create an array of filehandles?

by Punto (Scribe)
on Apr 25, 2000 at 07:36 UTC ( #8874=categorized question: print w/replies, xml ) Need Help??
Contributed by Punto on Apr 25, 2000 at 07:36 UTC
Q&A  > files


Answer: How can I create an array of filehandles?
contributed by perlmonkey

The trick is doing someting like:

open(FILE, "myfile.txt") $file = *FILE
After that you can use $file as a normal file handle so you can do:
print $file "Hello File"; close $file;
So here is how to put it all in an array:
#!/usr/bin/perl my @filehandles; #make array of 10 file handles for($i=0; $i<10; $i++) { #localize the file glob, so FILE is unique to # the inner loop. local *FILE; open(FILE, ">file$i.txt") || die; #push the typeglobe to the end of the array push(@filehandles, *FILE); } $count=0; #loop through the file handles. # treat $file as a normal file handle foreach $file (@filehandles) { print $file "File $count"; close $file; $count++; }
Answer: How can I create an array of filehandles?
contributed by CharlesClarkson

As of Perl 5.6.0 file handles can be autovivified. So it is possible to open a file like this:

open my $fh, '>', $file_name or die "Cannot open $file_name: $!";

This allows us to refer to the filehandle as $fh. The following sub returns a hash keyed to the file names:

my %handles = get_write_handles(qw/col1.txt col2.txt col3.txt/); sub get_write_handles { my @file_names = @_; my %file_handles; foreach (@file_names) { open my $fh, '>', $_ or next; $file_handles{$_} = $fh; } return %file_handles; }

Note that files that cannot be opened are not defined in the hash. Now the files can be referred to from %handles:

print { $handles{'in.txt'} } "something\n";

or:

foreach (values %handles) { print $_ "something\n"; }

To return an array we need to decide what happens if a file can't be opened. This sub dies:

sub get_read_handles { my @file_names = @_; my @file_handles; foreach (@file_names) { open my $fh, '<', $_ or die "Yikes $_: $!"; push @file_handles, $fh; } return @file_handles; }

While this will return undef for failed opens:

sub get_append_handles { my @file_names = @_; my @file_handles; foreach (@file_names) { if (open my $fh, '>>', $_) { push @file_handles, $fh; } else { push @file_handles, undef; } } return @file_handles; }
Answer: How can I create an array of filehandles?
contributed by chromatic

With the Symbol module, you can use gensym() to create a new, anonymous typeglob. Since that's the customary way to get at a filehandle, you can do something like this, to create an array of anonymous filehandles:

#!/usr/bin/perl -w use strict; use Symbol; my @handles; for (1 .. 2) { my $fh = gensym; open $fh, "test$_"; push @handles, $fh; } foreach my $handle (@handles) { print while (<$handle>); print "---\n"; close $handle; }
In a production environment, I wouldn't use a symbolic reference to a filename like I do in the first loop, but this is just an example.

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