for file in *.png; do mv $file ${file:l}; done
for file in *.png; do mv $file ${file:u}; done
for file in *.png; do mv $file ${file:t:r:u}; done
for file in *.png; do mv $file ${file:t:e:u}; done
for file in *.png; do mv $file ${file:l}; done
for file in *.png; do mv $file ${file:u}; done
for file in *.png; do mv $file ${file:t:r:u}; done
for file in *.png; do mv $file ${file:t:e:u}; done