How can I use Perl's "-i" option from within a program?

       "-i" sets the value of Perl's $^I variable, which in turn affects the behavior of "<>"; see perlrun for more details.  By modifying the appropriate variables
       directly, you can get the same behavior within a larger program.  For example:

            # ...
            {
               local($^I, @ARGV) = ('.orig', glob("*.c"));
               while (<>) {
                  if ($. == 1) {
                      print "This line should appear at the top of each file\n";
                  }
                  s/\b(p)earl\b/${1}erl/i;        # Correct typos, preserving case
                  print;
                  close ARGV if eof;              # Reset $.
               }
            }
            # $^I and @ARGV return to their old values here

       This block modifies all the ".c" files in the current directory, leaving a backup of the original data from each file in a new ".c.orig" file.