изменить имя файла в скрипте

Я устранил некоторые проблемы в сценарии и добавил встроенные комментарии. Посмотрите ниже:

#!/usr/bin/env bash

echo "Hello there, i am a little script so you can change a number of txt file names at once"

read -p "I would like to know your name before we start, what is your name? " NAME

echo "Well hello there $NAME, nice to meet you im Scripty"
echo "Let's start"

read -p "What type of file would you like to rename(txt,sh,etc...)" ANSWER

# ANSWER is a variable whose value must be accesses as $ANSWER.
# To avoid weird errors for ANSWERs with spaces in it, we put it in "double quotes":
case "$ANSWER" in
    [tT] | [tT][xX][tT])
        echo "You selected a TXT file type,Good job $NAME"
        ;;
    [sS] | [sS][hH])
        echo "You selected a SH file type,Good job $NAME"
        ;;

    # If none of the above applies it's always good to have a default case:
    *)
        echo "You picked something else. Not sure whether I can handle that..."
        ;;
# close/end the opening "case" statement:        
esac

# The original
#    FILES=$(ls *.$ANSWER)
# parses the output of the `ls` command. This is ok for one-shot
# commands if you know for sure that your filenames do not contain strange
# characters. But the proper way is to use _globbing_ and assign
# the filenames to a bash array:
FILES=(*.$ANSWER)

read -p "To what name you would like to change the file name?" NEW

# Iterating an array needs some special syntax:
for FILE in "${FILES[@]}"
  do 
    echo "Renaming $FILE to $NEW-$FILE"
    # Again "double quotes" because the filenames may contain spaces.
    # I prepended the line with "echo ..." so it does not do any harm.
    echo mv "$FILE" "$NEW-$FILE"
  done