Can bash make folders, based on a filename, and then move files into the folders?

Question

On /Desktop/a/ , there is a set of files:

DSCN1840.AVI00001.png
DSCN1840.AVI00002.png
DSCN1840.AVI00003.png
DSCN1841.AVI00001.png

What I would like is to have the following structure:

Desktop/a/DSCN1840/

  DSCN1840.AVI00001.png

  DSCN1840.AVI00002.png

  DSCN1840.AVI00003.png

Desktop/a/DSCN1841/

  DSCN1841.AVI00001.png

Answer 1

As a one-shot step, you could loop through all of the files and gather the desired subdirectory name; if that subdirectory doesn't already exist, create it; then move that file into that subdirectory:

for f in *.png
do
  subdir=${f%%.*}
  [ ! -d "$subdir" ] && mkdir -- "$subdir"
  mv -- "$f" "$subdir"
done

The key part of this is the parameter expansion in ${f%%.*}, which says to remove the longest matching portion (%%) of a period followed by anything, which effectively strips off, for example, the .AVI00003.png portions of the filenames, leaving only the leading directory indicator.