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

##</code><code>##

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

##</code><code>##

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

##</code><code>##

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 );
##</code><code>##

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 );