1. your error handling doesn't work:

open FILE, "foo" || die "can't open file"; # assume -T foo

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groups like 
open FILE, ("foo" || die ...)

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either use parantheses, or just or (or both):

open( FILE, $file) or die "Error: can't open file '$file': $!\n";

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2. better use while( my $line = <FILE> ) instead of the for my $line (<FILE>) (already mentioned) because while works in scalar context (i.e. it reads one line and then goes through the loop body, and then the next), whereas for uses listcontext (i.e. it reads the whole file into memory and then loops over the content which uses by far more RAM)

3. since FILE-handles are global, there may be the same problem like with each global variable: 

open( FH, $file1 ) or die $!;
while( my $line1 = <FH> ) {
  print "$file1: $line";
  open( FH, $file2 ) or die ...;
  while( my $line2 = <FH> ) {
    print "$file2: $line2";
  }
  close( FH );
} # while
close( FH );
<code>
<p>gives you an error because the first <code>close( FH );

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closes the filehandle so you can't continue reading in the outer loop. So better use lexical filehandles, because with them you don't need to check the whole script if this filehandle name is already used and active:

open( my $FILE, $file )
  or die "Error in reading file '$file': $!\n";
while( my $line = <$FILE> ) {
  # $line must be defined now, e.g.
  chomp( $line );
  print "$.: $line\n";
} # while
close( $FILE );

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Best regards,
perl -e "s>>*F>e=>y)\*martinF)stronat)=>print,print v8.8.8.32.11.32"

In reply to Re: nested <FILE> read returns undefined? by strat
in thread nested <FILE> read returns undefined? by argv

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