If you want to only use 1 filehandle you can always use a mixture of open/seek/tell/close to always re-use a single filehandle, see code below. Of course this is going to be really slow, as you will have to perform all 4 operations on every single line of each file.

Having a pool of open file handles would help some: as long as you are merging less files than the size of the pool you merge then the "natural way" (just read one line at a time from each filehandle), and if you need more, then you use the method below for files that you havent in the pool.

Does it make sense?

#!/usr/bin/perl -w
use strict;

use Fatal qw(open close); # so I don't have to bother testing them

my @files= @ARGV;
my %marker= map { $_ => 0 } @files;

while( keys %marker)
  { foreach my $file (@files)
      { if( exists $marker{$file})
          { open( my $fh, '<', $file);
            seek( $fh, $marker{$file}, 0); # the 0 means 'set the new 
+position in bytes to' $marker{$file}
            if( defined( my $line=<$fh>))
              { print $line;
                $marker{$file}= tell $fh;
              }
            else
              { delete $marker{$file}; }
            close $fh;
          }
      }
  }

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In reply to Re: Merging files by mirod
in thread Merging files by sk

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