sub func1{
WriteTOLog($Arga,$Argb,$Argc,$Argd); }
 ... do a bunch of things 
<code>
file b.pl
<code>
sub func2{
WriteTOLog($Arga,$Argb,$Argc,$Argd); }
 ... do a bunch of things 
<code>
file c.pl
<code>
sub func3{
WriteTOLog($Arga,$Argb,$Argc,$Argd); }
 ... do a bunch of things 
<code>
file log.pl
<code>
sub WriteToLog($,$,$,$){
  local ($var) = @_;
  # do its fike IO stuff
}

##</code><code>##

sub MyWriteToLog($,$,$,$){
  if ($FLAG eq 1) {
  local ($var) = @_;
  # do its fike IO stuff
    WriteTOLog($a,$b,$c,$d);
  } else {
   #do nothing or other things;
  }
}