how to "hang" file with the uso of cycle for - arrays

Question

I started now with the bash script and I'm trying to make a for loop that uses an array where there are the arguments passed to the script (2 or more files) trying to "hang" with the ">>" command, the first ones "n-1" files passed as argument to the last file (n) , writing the input files in the order from right to left
for example :
myscript.sh file1 file2 file3 file4
file4 will contain in sequence file3 file2 file1
arr=($#)
j=$#-1
for i in { j-1..0..1 }
do
cat arr[i] >> $[j]
done
I tried to do it this way but it doesn't work, can someone help me?

Answer 1

Try:
#!/bin/bash
n=$#
for i in $(seq $((n - 1)) -1 1) ; do
cat ${#:$i:1} >> ${#:$n:1}
done
Explanation:
seq $((n - 1)) -1 1 generates the numbers from $n - 1 to 1 in reverse order.
${#:$i:1} gives the element $i of the array of the arguments of the script.
Or, without seq:
#!/bin/bash
n=$#
for ((i = n - 1; i; i--)) ; do
echo "cat ${#:$i:1} >> ${#:$n:1}"
done
Or even shorter, with a while loop instead of a for loop, and maybe off topic for this reason:
#!/bin/bash
i=${#}
while ((--i)) ; do
echo "cat ${#:$i:1} >> ${#:$#:1}"
done

Answer 2

Not sure what about "hang", but this concatenates the first files to the last filename
cat "${#:0:$#}" > "${#: -1:1}"
this is slicing the the arguments.

Answer 3

You could print all arguments except the last one on separate lines, reverse the files order and then cat all of them into the file that is the last argument:
printf "%s\n" "${#:1:$#-1}" | tac | xargs cat > "${#: -1}"
The same using zero as the stream separator:
printf "%s\0" "${#:1:$#-1}" | tac -s '' | xargs -0 cat > "${#: -1}"
It would be very advisable to protect against the count of arguments less then 2, because when $# = 0 then ${#: -1} will be $0. Then $0 could be your shell with ex full path like /bin/bash, so > could overwrite your shell executable file!
So do:
if (($# >= 2)); then printf "%s\0" "${#:1:$#-1}" | tac -s '' | xargs -0 cat > "${#: -1}"; fi