Re^3: Reading two text files parallelly...

This is "comma operator". The "true" or "false" of the "while" only depends upon the state of $test2.

Oh, completely missed that.. All my tests had the second file longer than the first. ++ for the explanation! If I may take another moment of your time, I tried fixing that code from before, although now I think that I'm using one of those endless loops you adviced against:

while (my ($test1, $test2) = (scalar <$fh1>, scalar <$fh2>)) {
   last unless defined $test1 or defined $test2;
   ...
}
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I figure that the simplest fixes (for me, that is: Feel free to kick me on the right path) would be to either use the defined-or on the results of the readlines, replacing the undefs with the empty list, or move everything into a sub.

..actually, rather than talk about it:

defined-or'ing

while ( my $test1, $test2 ) = (scalar <$fh1> // (), scalar <$fh2> // (
+) ) {
    ...
}
[download]

sub'd

sub read_double_file {
    my ($fh1, $fh2)                 = @_;
    my ($line_file_1, $line_file_2) = (scalar <$fh1>, scalar <$fh2>);

   (defined $line_file_1 or defined $line_file_2) ? ($line_file_1 //= 
+'', $line_file_2 //= '') : ();
}

while ( my ($line_from_1, $line_from_2) = read_double_file($fh1, $fh2)
+ ) {
    ...
}
[download]

Is there a better approach? (For whatever reason, trying to solve this has been quite fun -- I'm even thinking about meddling with objects, just so I don't have to pass the filehandles over and over to the subs) Are the attempts so far horribly, terribly wrong?

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Re^4: Reading two text files parallelly... by Marshall (Canon) on Nov 11, 2010 at 16:48 UTC
Sounds like the main problem is to get very clear about what you want this program to do. If you want to just stop when both files are over, or when lines run out of one of them, another possibility is below. The while() takes an expression that evaluates to true/false. Nothing wrong with have more than one condition in an "and" statement. You can use "or" if you want. I don't see the need for anything fancy - try to keep it as easy to understand as possible. `#!/usr/bin/perl -w use strict; open (my $fh1, '<', "testa.txt") or die "cannot open testa"; open (my $fh2, '<', "testb.txt") or die "cannot open testb"; while ( defined (my $test1 = <$fh1>) and defined (my $test2 = <$fh2>) ) { print "both defined\n"; }` [download]	[reply] [d/l]

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Re^4: Reading two text files parallelly...
by Marshall (Canon) on Nov 11, 2010 at 16:48 UTC

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

open (my $fh1, '<', "testa.txt") or die "cannot open testa";
open (my $fh2, '<', "testb.txt") or die "cannot open testb";

while (   defined (my $test1 = <$fh1>) and 
          defined (my $test2 = <$fh2>)
      )
{
   print "both defined\n";
}
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