in reply to No such file or directory at R_loop2.pl line 19.

Why don't you replace the line as suggested below, to improve the error message : 
##OLD LINE# open FILE, '<', "@lines[$k]" or die $!;
open (FILE, '<', $lines[$k]) or die "Cannot open file $k='$lines[$k]' 
+:$!";

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Although I would replace 'FILE' my a localized handle : 'my $filehandle' .

             I hope life isn't a big joke, because I don't get it.
                   -SNL

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