perl -i -pe 's{window manager}{window mangler}g' /usr/bin/emacs

    $RECSIZE = 220; # size of record, in bytes 
    $recno   = 37;  # which record to update 
    open(FH, "+<somewhere") || die "can't update somewhere: $!"; 
    seek(FH, $recno * $RECSIZE, 0); 
    read(FH, $record, $RECSIZE) == $RECSIZE || die "can't read record $recno: $!"; 
    # munge the record 
    seek(FH, $recno * $RECSIZE, 0); 
    print FH $record; 
    close FH;