for file in $(find . -mindepth 1 -type f); do sed -i 's/remove\ this\ sentence/stringtoreplace/g' $file; done
Let's break it down.
$(find . -mindepth 1 -type f)
This will find every file starting in working directory, and return it as it's full path. Recursive in that you're searching a minimum depth of one (same directory) or more subdirs deep.
sed -i 's/remove\ this\ sentence/stringtoreplace/g'
-i modify file in-place
/g all occurrences of "remove this sentence" in lines as they're read.
And then there's the "for" loop, which iterates over the files.
Probably easier
Another way this can be done is by:
find . -mindepth 1 -type f -exec sed -i 's/remove\ this\ sentence/stringtoreplace/g' {} \;
...which is the same thing. Here, we're just using find to find the files and execute the sed replace in-place command on each one found.
sudo
. It's not a panacea for "I don't know what I'm doing so guess harder". Start by trying to change one file in the current directory. Then extend to all files in current directory. Then extend to the full directory tree. See where you get stuck. Read and try the suggestions in the link you've been given. – Chris Davies Feb 16 '17 at 07:39