# always check the results of an open()
open (FILE, $filename) or die "unable to open $filename for input: $!";

while (<FILE>) {

  # [1] omit line from output if it matches:
  # (make `[^.]*' more specific if only certain words should match)
  next if m~<!--\s*#include virtual\s*=\s*"/global_nav_[^".]*.ssi"\s*-->~;

  chomp;

  # [2]
  if (m!<body[^>]*>!i ... m!</body[^>]*>!i) { # modify body lines only
    # [3] replace .html with .asp in anchors in this line
    s~(href\s*=\s*")    # capture beginning of anchor in $1
      (?!http://)       # _not_ followed by http://
      ([^"]+)           # capture base of filename in $2
      \.html            # match .html
    ~${1}${2}.asp~gix;  # make substitution, global
  }

  print OUTFILE;

}