Shell by Example: Arithmetic

Shell by Example: Arithmetic POSIX + Bash

Shell scripting supports arithmetic operations through several mechanisms. This example covers the main ways to do math in shell scripts. POSIX arithmetic expansion with `$(( ))`:	Edit `#!/bin/sh echo "Basic arithmetic with \$(( )):" echo " 5 + 3 = $((5 + 3))" echo " 10 - 4 = $((10 - 4))" echo " 6 * 7 = $((6 * 7))" echo " 20 / 4 = $((20 / 4))" echo " 17 % 5 = $((17 % 5))" # Modulo (remainder)`
	Output: Basic arithmetic with $(( )): 5 + 3 = 8 10 - 4 = 6 6 * 7 = 42 20 / 4 = 5 17 % 5 = 2

Variables in arithmetic (no `$` needed inside):	Edit `#!/bin/sh x=10 y=3 echo "With variables (x=$x, y=$y):" echo " x + y = $((x + y))" echo " x * y = $((x * y))" echo " x / y = $((x / y))" # Integer division echo " x % y = $((x % y))"`
	Output: With variables (x=10, y=3): x + y = 13 x * y = 30 x / y = 3 x % y = 1

Compound assignment:	Edit `#!/bin/sh count=0 count=$((count + 1)) echo "After increment: count = $count"`
	Output: After increment: count = 1

Bash Bash provides shorter increment/decrement:	Edit `#!/bin/bash ((count++)) ((count--)) ((count += 5)) ((count *= 2))`

Comparison operators (return 1 for true, 0 for false):	Edit `#!/bin/sh a=5 b=10 echo "Comparisons (a=$a, b=$b):" echo " a < b: $((a < b))" echo " a > b: $((a > b))" echo " a == b: $((a == b))" echo " a != b: $((a != b))" echo " a <= b: $((a <= b))" echo " a >= b: $((a >= b))"`
	Output: Comparisons (a=5, b=10): a < b: 1 a > b: 0 a == b: 0 a != b: 1 a <= b: 1 a >= b: 0

Logical operators:	Edit `#!/bin/sh echo "Logical operators:" echo " 1 && 1 = $((1 && 1))" echo " 1 && 0 = $((1 && 0))" echo " 1 \|\| 0 = $((1 \|\| 0))" echo " !0 = $((!0))" echo " !1 = $((!1))"`
	Output: Logical operators: 1 && 1 = 1 1 && 0 = 0 1 \|\| 0 = 1 !0 = 1 !1 = 0

Bitwise operators:	Edit `#!/bin/sh echo "Bitwise operators:" echo " 5 & 3 = $((5 & 3))" # AND echo " 5 \| 3 = $((5 \| 3))" # OR echo " 5 ^ 3 = $((5 ^ 3))" # XOR echo " ~5 = $((~5))" # NOT echo " 4 << 2 = $((4 << 2))" # Left shift echo " 16 >> 2 = $((16 >> 2))" # Right shift`
	Output: Bitwise operators: 5 & 3 = 1 5 \| 3 = 7 5 ^ 3 = 6 ~5 = -6 4 << 2 = 16 16 >> 2 = 4

Ternary operator is a shorthand way to write an if-else statement. The syntax is: $((condition ? expression1 : expression2)) If the condition is true, the expression1 is evaluated and returned. Otherwise, the expression2 is evaluated and returned. This example shows how to use the ternary operator to find the maximum of two numbers.	Edit `#!/bin/sh a=10 b=20 max=$((a > b ? a : b)) echo "Max of $a and $b: $max"`
	Output: Max of 10 and 20: 20

Parentheses for grouping:	Edit `#!/bin/sh echo "Order of operations:" echo " 2 + 3 * 4 = $((2 + 3 * 4))" echo " (2 + 3) * 4 = $(((2 + 3) * 4))"`
	Output: Order of operations: 2 + 3 * 4 = 14 (2 + 3) * 4 = 20

Bash Different bases:	Edit `#!/bin/bash echo "Different bases:" echo " Hex 0xFF = $((0xFF))" # works in sh and bash echo " Octal 077 = $((077))" # works in sh and bash echo " Binary 2#1010 = $((2#1010))" # bash-specific`
	Output: Different bases: Hex 0xFF = 255 Octal 077 = 63 Binary 2#1010 = 10

Using `expr` (older method, POSIX):	Edit `#!/bin/sh echo "Using expr:" echo " 5 + 3 = $(expr 5 + 3)" echo " 10 - 4 = $(expr 10 - 4)" echo " 6 \* 7 = $(expr 6 \* 7)" # Note: * must be escaped echo " 20 / 4 = $(expr 20 / 4)"`
	Output: Using expr: 5 + 3 = 8 10 - 4 = 6 6 \* 7 = 42 20 / 4 = 5

`expr` for string length and matching:	Edit `#!/bin/sh str="hello" echo " Length of '$str': $(expr length "$str")"`
	Output: Length of 'hello': 5

Floating-point arithmetic requires external tools:	Edit `#!/bin/sh echo "Floating-point with bc:" echo " 5.5 + 3.2 = $(echo "5.5 + 3.2" \| bc)" echo " 10 / 3 = $(echo "scale=2; 10 / 3" \| bc)" echo " sqrt(2) = $(echo "scale=4; sqrt(2)" \| bc)"`
	Output: Floating-point with bc: 5.5 + 3.2 = 8.7 10 / 3 = 3.33 sqrt(2) = 1.4142

Bash Bash’s `let` command can be used to perform arithmetic operations.	Edit `#!/bin/bash let "result = 5 + 3" echo "let result: $result" x=5 let "x++" echo "let x: $x" let "y = x * 2" echo "let y: $y"`
	Output: let result: 8 let x: 6 let y: 12

Bash Bash’s `$(( ))` can be used for arithmetic in conditions.	Edit `#!/bin/bash x=10 if ((x > 5)); then echo "x is greater than 5" fi`
	Output: x is greater than 5

Bash Declare integer variables with `declare -i` to automatically evaluate arithmetic expressions.	Edit `#!/bin/bash declare -i num num="5 + 3" # Automatically evaluated echo "Declared int: $num"`
	Output: Declared int: 8

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