estet.sh

#! /bin/bash
#  Ascii to Small Latin
#  Usage: thisscript <in.txt >out.txt
#  or:    thisscript <<<"some-text"
while IFS= read -d$'\0' -r -n1 c                    # read single bytes
do
  printf -vd "%d" "'$c"                             # decimal ordinal
  (( d >= 65 && d <=90 )) && (( d += 65248 ))       # A-Z -> small latin
  ((d >= 97 && d <= 122 )) && (( d += 65248 ))      # a-z -> small latin
  (( d > 255 )) && printf \\U$(printf "%08X" "$d")  # Unicode UTF-8
  (( d < 256 )) && printf "%s" "$c"                 # Echo other stuff
done