Converting read variables to lowercase in sh on ubuntu

It's probably because you didn't assign the translated output to a variable yet. Also I suggest quoting your variables around doublequotes to prevent word splitting and pathname expansion.

foobar=$(echo "$foobar" | tr '[:upper:]' '[:lower:]')

If you're using case and you just need to check if an input is y or Y either way you can use a glob pattern like this. There's no need to transliterate it to lowercase form.

case $foobar in[yY])    echo "User said yes."    ;;*)    echo "User said no."    ;;esac

Also you can somehow suppress showing user input by using -s:

read -s foobar

As a whole to make your code work well in both bash and sh you should already remove the part which is bash specific:

#!/bin/bashecho "Please enter a word:"read -s foobarfoobar=$(echo "$foobar" | tr '[:upper:]' '[:lower:]')echo "$foobar"

And if it's just about showing the smaller form, you can skip the assignment. But don't use another echo along with it:

#!/bin/bashecho "Please enter a word:"read -s foobarecho "$foobar" | tr '[:upper:]' '[:lower:]'

Another alternative form from case. This is meant to be POSIX compatible.

if [ "$foobar" = y ] || [ "$foobar" = Y ]; then    echo "User said yes."else    echo "User said no."fi

In bash it could be simply like this. It would work even in earlier versions that doesn't support ${parameter,,} feature.

if [[ $foobar == [yY] ]]; then    echo "User said yes."else    echo "User said no."fi