Linux Ubuntu change extension to lowercase   

Changing extension to lower case with linux for multiple text, csv files and other. So all you need to do is to go to the folder with your text files and then run the command:

• text files

 for i in $( ls *.TXT ); do echo $i; mv $i  ${i%%.TXT}.txt; done

• csv files

for i in $( ls *.CSV ); do echo $i; mv $i  ${i%%.CSV}.csv; done

You can rename or add back up to multiple files as well:

for i in $( ls *.TXT ); do echo $i; mv $i  ${i%%.TXT}.txt.bak; done