| Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting | ||
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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" # 4031 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 # Error message output: 50 # numbers.sh: let: oct = 081: value too great for base (error token is "081") 51 # Octal numbers use only digits in the range 0 - 7. 52 53 exit 0 # Thanks, Rich Bartell and Stephane Chazelas, for clarification. |