open (CF,"$requestControlFile") || die("can't open $requestControlFile -> $!");  
my @data = <CF>; 
close(CF); 
for (@data) { 
   #do something 
} 
open (CF,">$requestControlFile") || die("can't open $requestControlFile -> $!"); 
for (@data) { 
   print CF $_; 
} 
close(CF);

use Fcntl ':flock'; 
 
open (CONTROLFILE,"+<$requestControlFile") 
  || die("can't open $requestControlFile -> $!");  
 
flock CONTROLFILE, LOCK_EX; 
 
my @file = <CONTROLFILE>; 
# do something to the data in @file 
# then when you want to write it back... 
 
seek CONTROLFILE, 0, 0; 
truncate CONTROLFILE, 0; 
print CONTROLFILE @file; 
close CONTROLFILE;