Custom unix command combination assigning to variable - bash

Question

I want to make UNIX script, which will automatically move my working directory files to newly created directories.
Example: In you dir you got files:
001-file.html,
001-file.rb,
002-file.html,
002-file.rb
And 2 files will be moved to ./NewDir/001-file and another 2 to ./NewDir/002-file
My problem is that after I get correct string from Unix commands I cannot assign it to variable.
Here is my code:
clear
echo "Starting script"
echo "Dir = "$(pwd)
read -p "Please enter count(max '999') of different file groups:" max_i
read -p "Enter new dir name:" outer_dir_name
for ((i=0; i<=$max_i;i++)) do
a1=$(($i/100))
a2=$((($i-$a1*100)/10))
a3=$(($i-($a2*10)-($a1*100)))
inner_dir_name=$((ls *[$a1][$a2][$a3]* 2>/dev/null | head -n 1 | cut -f1 -d"."))
echo $inner_dir_name
echo "--------------"
done

Answer 1

One pair of round parentheses is enough for command substitution.
inner_dir_name=$(ls *[$a1][$a2][$a3]* 2>/dev/null | head -n 1 | cut -f1 -d".")

Answer 2

It looks like you're going about the operation the hard way. I would probably do something like this, assuming that there are no spaces in the file names:
ls | sed 's/\..*$//' | sort -u |
while read prefix
do
mkdir -p $outer_dir_name/$prefix
mv $prefix.* $outer_dir_name/$prefix
done
The ls could be made more precise with:
ls [0-9][0-9][0-9]-file.*
If I was worried about blanks and other odd-ball characters in the file names, I'd have to use something more careful:
for file in [0-9][0-9][0-9]-file.*
do
prefix=${file%%.*}
[ -d "$outer_dir_name/$prefix" ] || mkdir -p "$outer_dir_name/$prefix"
mv "$file" "$outer_dir_name/$prefix"
done
This executes more mv commands, in general.