. Write a shell function called octal that converts octal numbers given as command-line arguments to decimal numbers and prints them out, one per line

$ octal 10 11 12
8
9
10
(Korn shell users, remember that if you assign a decimal number to a variable when it's declared – for example, typeset –i d=10#0 – assignments to this variable from other bases are automatically converted to decimal.)

This one's easier than it seems. Here's a simple solution:
#!/bin/sh

# octal - given octal values, display as decimal values

for octalnum
do
(( i = 8#$octalnum ))
echo $i
done

exit 0