bash sed find and replace - open to bidding

I need a bash script to do this: I have folder that contain html files and subfolders. now files name as [login to view URL], [login to view URL] etc. i want to replace the original file name with the title tag of the file ( instead of the space between the words i would like to add "_". then replace all links in all folder that contain the original name with the new title name. example of title - <title>admin/environment/php some text</title> change to <title>php_some_text</title> then to replace all links in all files that contain the old links to the new file name that will be php_some_text.html. all my needs have a solutions in my script but don't know how to replace the link all over to the new file name. my script: #!/bin/bash cd /var/www/clients/client1/web2/web/docs/31/en find . -name "*.html" > [login to view URL] while read -r filepath ; do # Considering the subfolder can have spaces, # We will start by separating the filename # And dirname folderpath=`dirname "$filepath"` filename=`basename "$filepath"` # With GNU GREP new_name=$(grep -oP '<title>\K.+?</title>' "$filepath" | sed 's#</title>##' | tr ' ' '_' ) #echo new_name=$(grep -oP '<title>\K.+?</title>' "$filepath" | sed 's#</title>##' | tr ' ' '_' ) # With BSD GREP (for who need the info) # new_name=$(grep -o '<title>.*</title>' $filepath | sed -e 's/<title>\(.*\)<\/title>/\1/g' | sed -e 's/$filename/$new_name/g' | tr ' ' '_') #if [[ $new_name = */* ]]; then echo "/${new_name##*}"; else echo "$new_name"; fi mv -v "$filepath" "$folderpath/`basename $new_name`.html" ### command that i tried to solve the link url issue #find /var/www/clients/client1/web2/web/docs -type f -exec sed -i 's/$filename/$new_name/g' {} \; #grep -rl '$filename' /var/www/clients/client1/web2/web/docs/31/en | xargs sed -i 's/$filename/$new_name/g' *.html #sed -i 's/$filename/$new_name/gi' *.html done < [login to view URL] Thank you