Substring failing in shell script

Question

for file in *.csv
do
  split -n 5 -d -a 1  "$file" "$file"
  for each in $(seq -w 2 3)
  do
        echo $each
        filestem="$file$each"
        len_filestem=${#filestem}
        subs=substr(len_filestem,3,4)
        echo $subs
        echo $filestem
  #awk '{filename = "wrd." int((NR-1)/10000) ".txt"; print >> filename}' $file--$each
  awk -v filestem= "{$filestem}" '{filename = substr(filestem,3,5};  print >> filename}' $filestem

  done
done

Im trying to find the substring of a string but my script is failing in substr(len_filestem,3,4)

Answer 1

The error is the space after the =:

-v filestem= "{$filestem}"