In essence it would look like this:

#!/usr/bin/perl

# lives tracks the number of times the program has run.
# the line number is stored for later use in an array
# called @program, so if consensual hackers decide to 
# rearrange, the program can still find the variable.

$lives = 0; $line{lives} = (__LINE__ - 1);

# The source code of the file is read into @program
open( THIS, "$0" );
 @program = <THIS>;
close( THIS );

# The line number from earlier points at the line of code
#  storing the variable '$lives'.
# Render the line and store it back into @program over the 
#  old line of code. 
$program[ $line{lives} ] =
 '$lives = ' . ($lives+1) . 
  '; $line{lives} = (__LINE__ - 1);' . "\n";

# Output the program's slightly modified source 
#  code over the old file.
open( THIS, ">$0" );
 print THIS @program;
close( THIS );

# Clear the screen buffer and 'exec' the modified source.
system( 'clear' );
exec( $0 ); # exec() does not return to this program.

print "This does not get displayed.";
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abatek~