undef $/;
open(IN, "< 1.txt") ;
$str = <IN>;
close(IN);

$str =~ s#\n(.+?)\n#\n\$exec \= \$ENV\{EXEC\}\n$1\n#gsi;
open(OUT, "> 2.txt") ;
print OUT $str;

input:
*********
hai
this
is
the
test
input
sample


output:
**********
hai
$exec = $ENV{EXEC}
this
is
$exec = $ENV{EXEC}
the
test
$exec = $ENV{EXEC}
input
sample