if you need to track the number of lines between MULTIPLE 'energy lines' then a modification to the above like this might be in the right direction ...

#!/usr/local/perl5/bin/perl
open F, "<./fff";

$b=$energy=0;
@between = ();
while (<F>) {
    if (/energy/i) {
        $between[$energy]=$b;
        $energy++;
        $b = 0;
    }
    else {$b++}
}
$between[$energy]=$b;
my $i;
printf("Before Energy    1        : %3d lines occur\n",$energy,$betwee
+n[0]) if ($between[0] > 0);
for($i = 1; $i < $energy; $i++) {
 printf("Between Energy %3d and %3d: %3d lines occur\n",$i,$i+1,$betwe
+en[$i]);
}
printf("After Energy   %3d        : %3d lines occur\n",$energy,$betwee
+n[$energy]);
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