open my $in_fh, '<', '/home/nikl123/indri-5.6/runquery/trec7_4collecti
+ons.txt'
  or die $!;
print scalar <$in_fh>;
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This will open a file and print the first line. You don't need a loop to read the first line of a file, and you don't need to split on newlines if you only read one line. In fact, you don't even need to print a newline explicitly, as each line of a file will end in one, except for the last line (unless the first line is the last line).

Or how about this?

use IO::All;
print io('/home/nikl123/indri-5.6/runquery/trec7_4collections.txt')->g
+etline;
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