Octal is a counting system based on eight digits (0,1, 2, 3, 4, 5, 6, 7). To expand an octal number to decimal, multiply each digit in the number with the corresponding power of eight. The following shell script demonstrates this: #!/bin/bash # Take an octal number and output it's decimal version octal=$1 length=`echo $octal | wc -c | tr -d " "` power=1 while [ $length -gt 2 ] do power=$(( $power * 8 )) length=$(( $length - 1 )) done decimal=0 while [ "%$octal%" != "%%" ] do digit=`echo $octal | cut -b 1` echo -n "Octal = $octal, Digit = $digit, Power = $power, Value = " value=$(( $digit * $power )) echo $value decimal=$(( $decimal + value )) power=$(( $power / 8 )) octal=`echo $octal | sed 's/^.//'` done echo "" echo "Result = $decimal" The following shell script example shows how to convert a decimal number to octal from first principles: #!/bin/bash # Take a decimal number and output it's octal quotient=$1 while [ $quotient -ne 0 ] do remainder=$(( $quotient % 8 )) octal="$remainder$octal" quotient=$(( $quotient / 8 )) done echo $octal Computer Engineering Hardware Design by M Morris Mano published by Prentice Hall 1988 Binary Decimal Hexadecimal Entry created: Thu Mar 20 15:20:12 EST 2003 Entry owner: Michael Still (mikal@stillhq.com) Status: Finalized