# 8.2. Numerical Constants

A shell script interprets a number as decimal (base 10), unless that number has a special prefix or notation. A number preceded by a 0 is octal (base 8). A number preceded by 0x is hexadecimal (base 16). A number with an embedded # evaluates as BASE#NUMBER (with range and notational restrictions).

Example 8-4. Representation of numerical constants

 ``` 1 #!/bin/bash 2 # numbers.sh: Representation of numbers in different bases. 3  4 # Decimal: the default 5 let "dec = 32" 6 echo "decimal number = \$dec" # 32 7 # Nothing out of the ordinary here. 8  9  10 # Octal: numbers preceded by '0' (zero) 11 let "oct = 032" 12 echo "octal number = \$oct" # 26 13 # Expresses result in decimal. 14 # --------- ------ -- ------- 15  16 # Hexadecimal: numbers preceded by '0x' or '0X' 17 let "hex = 0x32" 18 echo "hexadecimal number = \$hex" # 50 19 # Expresses result in decimal. 20  21 # Other bases: BASE#NUMBER 22 # BASE between 2 and 64. 23 # NUMBER must use symbols within the BASE range, see below. 24  25 let "bin = 2#111100111001101" 26 echo "binary number = \$bin" # 31181 27  28 let "b32 = 32#77" 29 echo "base-32 number = \$b32" # 231 30  31 let "b64 = 64#@_" 32 echo "base-64 number = \$b64" # 4094 33 # 34 # This notation only works for a limited range (2 - 64) 35 # 10 digits + 26 lowercase characters + 26 uppercase characters + @ + _ 36  37 echo 38  39 echo \$((36#zz)) \$((2#10101010)) \$((16#AF16)) \$((53#1aA)) 40  # 1295 170 44822 3375 41  42  43 # Important note: 44 # -------------- 45 # Using a digit out of range of the specified base notation 46 #+ will give an error message. 47  48 let "bad_oct = 081" 49 # numbers.sh: let: oct = 081: value too great for base (error token is "081") 50 # Octal numbers use only digits in the range 0 - 7. 51  52 exit 0 # Thanks, Rich Bartell and Stephane Chazelas, for clarification.```