bash to rename files with sequential numbers

bash file rename

//Beauty in one line

ls | cat -n | while read n f; do mv "$f" "$n.extension"; done 
change extension with desired PNG, Jpg or some-other.


//Try to use a loop, let, and printf for the padding:

a=1
for i in *.jpg; do
  new=$(printf "%04d.jpg" "$a") #04 pad to length of 4
  mv -- "$i" "$new"
  let a=a+1
done
//use mv -i -- "$i" $new" if you do not want to automatically overwrite existing files.