Re: parallel reading

[Zaxo]

in reply to parallel reading

Here's another,

open my $out, '>', 'ABC' or die $!;
{
    local $_;

    open my $A, '<', 'A' or die $!;
    open my $B, '<', 'B' or die $!;
    open my $C, '<', 'C' or die $!;

    no warnings 'uninitialized';

    while ($_ = <$A> . <$B> . <$C>) {
        s/\n//g;
        print $out $_, "\n";
    }
}
close $out or warn $!;

That will let the files have different numbers of lines. Memory use is small, and independent of file size.

Update: Repaired the thinko blazar++ spotted. Empty lines are not a problem - we don't chomp, so they retain newlines until we s/// them gone. I like blazar's extension to different numbers of files.

[blazar]

Nice approach. And my be merged with mine, e.g.:

#!/usr/bin/perl -l

use strict;
use warnings;

my @fh=map {
    open my $fh, '<', $_ or die "Can't open `$_': $!\n";
    $fh } @ARGV;

no warnings 'uninitialized';
print while $_=join '',
  map { chomp(my $line=<$_>); $line } @fh,

__END__

However:

• you should s/undefined/uninitialized/;
• it may not be fully reliable if empty lines are to be expected in the files.

Update: the second point was a thinko as Zaxo pointed out.