Change some ASP code to PHP code in all files

There are various ways of doing this, I would recommend taking advantage of Perl's quotemeta function.

First, make a tab separated text file containing the search patterns in the first column and their replacement in the second:

$ cat pats.txt                     
<% if request("page") = "" then %>  <?php if(!isset($_GET['page']) || !$_GET['page']){ ?>
<% elseif request("page") = "*" then %> <?php } elseif($_GET['page'] == '*'){ ?>
<% end if %>    <?php } ?>

I created a test file whose contents are:

$ cat foo.asp 
<% if request("page") = "" then %>
<% elseif request("page") = "*" then %>
<% end if %>

And Perl to the rescue:

find . -name "*.php" | while IFS= read -r file; do
  perl -i.bak -e 'open(A,"pats.txt");
             while(<A>){chomp; @a=split(/\t/); $k{quotemeta($a[0])}=$a[1]}
             while(<>){ 
              foreach $pat (keys(%k)){
                s/$pat/$k{$pat}/;
              } 
             print}' $file;
done

Perl's -i flag works just like in sed, you can specify an optional backup suffix. In the example above, a file called foo.php.bak will be created for each processed file. Use -i alone if you don't want the backups.

EXPLANATION:

The script will read the patterns and replacements and save the patterns as keys of a hash (%k) where the replacements are the values. The quotemeta function escapes all non ASCII (not matching [A-Za-z_0-9]) characters.

The script them opens the second file, looks for each pattern in each line and replaces accordingly. Since the search patterns has been escaped by quotemeta it is correctly recognized.

NOTES

This is obviously not the most efficient way of doing this since it will have to look for each of the patterns on each line. Still, it works and is much simpler than mucking about trying to manually escape everything.

The script will fail for files with new lines in the names. I assume that won't be a problem here.