How can I create a file in each folder?

Assuming you have a list of your project directories in a file called "projects.txt", you can do this (for bash and zsh)

for i in $(cat projects.txt)
do
  touch $i/index.html
done

To create your projects.txt, you can use the find command. You could replace the cat directly with a find invocation but I thought it more clear to separate the two operations.

cd /project_dir && find . -type d -exec touch \{\}/index.htm \;

HTH

find . -type d -exec touch {}/index.html \;

This'll create an index.html in . and all subdirectories.

I know it's an old question but none of the current answers allow to add some sample code, here my solution:

#create a temp file
echo "<?php // Silence is golden" > /tmp/index.php

#for each directory copy the file
find /mydir -type d -exec cp /tmp/index.php {} \;

#Alternative : for each directory copy the file where the file is not already present
find /mydir -type d \! -exec test -e '{}/index.php' \; -exec cp /tmp/index.php {} \;