Bash Calculator

.bashrc

# Bash Calculator using command_not_found_handle
# Version: 7.5.0
# Uses = as calculator prefix: =2+2, ="(2+3)*4", =[2+3]*4, ?sqrt(16)
# For division, use space: = 10/3
# Or quote: ='10/3'

calc_internal() {
    local expression="$*"

    # If expression is empty, show usage
    if [[ -z "$expression" ]]; then
        echo "Calculator: =expression"
        echo "Examples: =2+2, =\"(2+3)*4\", =\"sqrt(16)\", =.5*2"
        echo "          =2+2, =\"(2+3)*4\" (for simple expressions)"
        return 1
    fi

    # Convert brackets to parentheses
    expression="${expression//\[/(}"
    expression="${expression//\]/)}"

    # Add leading zero to decimals starting with .
    if [[ "$expression" =~ ^-?\. ]]; then
        if [[ "$expression" =~ ^-\. ]]; then
            expression="-0.${expression:2}"
        else
            expression="0.${expression:1}"
        fi
    fi

    # Fix other decimal cases (after operators)
    expression=$(echo "$expression" | sed -E '
        s/\(\./(0./g;
        s/\+\./+0./g;
        s/-\./-0./g;
        s/\*\./*0./g;
        s/\/\./\/0./g;
    ')

    # Calculate using bc
    local result
    result=$(bc -l <<< "scale=3; $expression" 2>&1)

    # Check for bc errors
    if [[ "$result" =~ ^\(standard_in\) ]] ||
       [[ "$result" =~ [Ee]rror|[Dd]ivide.*[Zz]ero|[Ss]yntax ]]; then
        echo "Math error: Invalid expression" >&2
        return 1
    fi

    # Clean result: remove trailing zeros and decimal point
    result=$(echo "$result" | sed -E '
        s/\.[0]+$//
        s/\.$//
        s/^[[:space:]]+//
        s/[[:space:]]+$//
    ')

    [[ -z "$result" ]] && result="0"
    [[ "$result" == "-" ]] && result="0"

    echo "$result"
}

# This hook allows to use '=expr' (no space) beside '= expr' (with space).
command_not_found_handle() {
  # Check if command is "=".
  if [[ "$*" =~ ^= ]]; then
    # Remove spaces and "=".
    expression=$(echo "$@" | sed 's/ //g' | sed 's/=//g');
    calc_internal "$expression"
    return $?
  fi
  echo "bash: $*: command not found" >&2
  return 127
}

export -f command_not_found_handle 2>/dev/null || true

# Test function
test_bash_calc() {
    echo "Testing Bash Calculator - Version 7.5.0"
    echo "=================================================="
    echo ""
    # Store original function
    local original_handle=$(declare -f command_not_found_handle)

    # Temporarily unset to avoid recursion
    unset -f command_not_found_handle 2>/dev/null

    echo "Test cases (use space after =):"
    echo "  =2+2: $(calc_internal '2+2')"
    echo "  =(2+2): $(calc_internal '(2+2)')"
    echo "  =(2+3)*4: $(calc_internal '(2+3)*4')"
    echo "  =[2+3]*4: $(calc_internal '[2+3]*4')"
    echo "  =10/3: $(calc_internal '10/3')"
    echo "  =.5*2: $(calc_internal '.5*2')"
    echo "  =-.5*2: $(calc_internal '-.5*2')"
    echo "  =sqrt(16): $(calc_internal 'sqrt(16)')"
    echo "  =2*3*4: $(calc_internal '2*3*4')"
    echo "  =(5.5+2.3)*2: $(calc_internal '(5.5+2.3)*2')"
    echo "  =2^8: $(calc_internal '2^8')"
    echo "  =4*a(1): $(calc_internal '4*a(1)')"
    echo "  =s(0): $(calc_internal 's(0)')"
    echo "  =2++3: $(calc_internal '2++3')"
    echo "  =10/0: $(calc_internal '10/0')"
    echo "  =: $(calc_internal '')"

    echo ""
    echo "Simple expressions (no space, no /):"
    echo "  =2+2: $(calc_internal '2+2')"
    echo "  =2*3: $(calc_internal '2*3')"

    # Restore original function
    eval "$original_handle"
    export -f command_not_found_handle 2>/dev/null || true

    echo "=================================================="
    echo "Usage: =expr"
    echo "Test complete."
}