bc - macOS

Overview

bc (Basic Calculator) is a command-line calculator included in macOS that supports arbitrary precision arithmetic. It operates in two modes: the default infix notation mode and an optional reverse Polish notation (RPN) mode. bc is widely used for mathematical calculations that require more precision than floating-point arithmetic offered by typical programming languages.

Syntax

The basic syntax of the bc command is:

bc [options] [file...]
  • [file…]: Optional. Files containing bc code that should be executed as if they were typed on the command line.

Options/Flags

  • -l, –mathlib: Load the standard math library. This option also configures the scale (number of decimal places for division) to 20 by default.
  • -i, –interactive: Force interactive mode. This is helpful when piping input from other programs but still require user interaction.
  • -q, –quiet: Do not print the normal GNU bc welcome when entering interactive mode. Useful for scripts or when bc’s output needs to be parsed.
  • -s, –standard: Invoke POSIX standard bc, which disables certain GNU extensions for compatibility with the traditional UNIX version of bc.
  • -w, –warn: Provide warning messages for extensions to POSIX bc.
  • -h, –help: Display help information.

Examples

  1. Basic Calculation:

    echo "3 + 4" | bc

    Outputs 7.

  2. Using Math Library:

    echo "scale=10; l(10)" | bc -l

    Calculates the natural logarithm of 10 with 10 decimal places.

  3. Interactive Mode Calculation:
    Start bc in interactive mode:

    bc -l

    You can now enter calculations directly into the console.

  4. Script Example:

    #!/usr/bin/env bc -l
scale=10
a=5.75
b=2.35
a+b
quit

    This script adds two numbers and exits.

Common Issues

  • Scaling Error: Users may forget to set the scale for divisions, resulting in truncated integers. Always set scale before performing division if you need decimal results.
  • Non-interactive Hangs: When running non-interactively without providing input via a pipe or file, bc might appear to hang. Ensure you provide input through one of these mechanisms or use bc interactively.

Integration

bc can be integrated with shell scripts or combined with other tools like awk for powerful data processing tasks:

echo "scale=2; $(cat values.txt)" | bc

This example reads calculations from a file, modifies the scale, and processes the calculations.

  • dc: A reverse polish desk calculator.
  • awk: A pattern scanning and processing language, also capable of performing arithmetic operations.

For more detailed information, consult the bc man page by running man bc in your terminal.