var=${var,,}

se man bash :)

#!/bin/sh

if [ -n "$1" ]; then
let count=0
while [ "$1" ]; do
f=”$1″
shift
if [ -f "$f" ]; then
lc=${f,,}
if [ "$lc" != "$f" ]; then
mv “$f” “$lc”
((count++))
fi
fi
done
echo “Result: $count files have been changed.”
else
echo “Usage: lowerit file(s)”
fi