use strict;
use warnings;

my $fileText;
do {local $/; $fileText = <DATA>};

my $rxOK = qr
   {(?xms)
      ^First\sName
      (?=.*?^Last\sName)
   };

print
   $fileText =~ $rxOK
   ? qq{File OK\n}
   : qq{File BAD\n};

__END__
.....
First Name
.....
.....
Last Name
.....

##</code><code>##

my $fCnt = $fileText =~ /First\sName/g;
die qq{"First Name" occurs more than once\n}
   if $fCnt > 1;

my $lCnt = $fileText =~ /Last\sName/g;
die qq{"Last Name" occurs more than once\n}
   if $lCnt > 1;

##</code><code>##

my @fCnt = $fileText =~ /First\sName/g;
die qq{"First Name" occurs more than once\n}
   if @fCnt > 1;

my @lCnt = $fileText =~ /Last\sName/g;
die qq{"Last Name" occurs more than once\n}
   if @lCnt > 1;