Alpha sequence

When doing a quick little shell script the seq command is very handy to generate a list of numbers but all too often I find that I need a sequence of letters and there is no alphabetical version of seq. There are hundreds of examples on the Internet of how to do this in almost every script language you can think of, this is my version in bash.

This version has the added feature of being able to run up a sequence of upper or lower case letter. The script only accepts one argument of the last letter, but could easily be expanded to do all sorts of extra tricks.

#!/bin/bash

OUT=""
TARGET=$(echo ${1:0:1} | grep -i "[a-z]")
UPPER=$(echo $TARGET | tr "[a-z]" "[A-Z]")
START=97 # a
[ "$TARGET" = "$UPPER" ] && {
 START=65 # A
}
while [ "$OUT" != "$1" ]; do
 OUT=$(awk 'BEGIN{printf "%c",'${START}'}')
 echo -n "$OUT "
 let "START=$START+1"
done

Examples:

$ alphaseq J
A B C D E F G H I J

$ alphaseq m
a b c d e f g h i j k l m