GNU bc Cheat Sheet


  • bc is a command-line calculator and primitive language
  • bc by default runs in integer mode (scale=0) and with no trig functions, running bc -l loads trig functions and sets scale to 20
  • bc can only take expressions on standard input or in files, not directly on the command line. One way to do a bc one-liner is echo 3+4 | bc .
  • This is a great collection of bc functions. funcs.bc and logic.bc are the basic ones. This is a collection of more sanely named basic scientific calculator functions.
  • useful bash aliases
mbc ()
  echo $@ | bc -l -q ~/bin/extensions.bc
alias bc="bc -l -q ~/bin/extensions.bc"

So now mbc '(3+5)/6' works as expected

  • bc uses readline so ⇑ and ⇓ (for history) and ctrl-r (for searching) work as expected.

Basic Usage

  • Any alphanumeric variable name is allowed once it starts with a letter.
  • There are 4 special variables
    • last - The value of the last printed number
    • scale - number of decimal places to display
    • ibase - base to be used for input values
    • obase - base to be used for output values
  • Any expression that is not an assignment is displayed and stored in the last variable.
  • Every value and every expression is a number. The assignment operator returns 0. Booleans are 0 / 1.
  • Basic + - / * = == work. % is modulo . ^ is integer exponentiation.
  • Predefined functions are :
    • s - sine , c - cosine
    • a - arctan , j(n,x) - Bessel function
    • l - natural log , e - e to the power of
    • length, scale, sqrt - as named
  • && , || , ! work as expected (return 0 or 1).

Advanced Usage

  • New functions are easy to define e.g.
    define log(x,y) {
      auto retval = l(y)/l(x)
      return retval

Note that the auto keyword is used to declare a local variable.

  • if(cond) else, while(cond) and for(init;cond;inc) control flow structures are all supported. break and continue are also supported.
  • read() is used to read a value from standard input. print() prints to standard output.
  • Arrays can be used by using [subscript] after the array name.
  • Special commands include quit, limits and warranty.
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