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| Chapter 2 UNIX Commands |

## bc

    bc [options] [files]

Interactively perform arbitrary-precision arithmetic or convert numbers from one base to another. Input can be taken from `files` or read from the standard input. To exit, type quit or `EOF`.

### Options

-c

  Do not invoke dc; compile only. (Since bc is a preprocessor for dc, bc normally invokes dc.)

-l

  Make available functions from the math library.

bc is a language (and compiler) whose syntax resembles that of C. bc consists of identifiers, keywords, and symbols, which are briefly described below. Examples follow at end.

### Identifiers

An identifier is a single character, consisting of the lowercase letters a-z. Identifiers are used as names for variables, arrays, and functions. Within the same program you may name a variable, an array, and a function using the same letter. The following identifiers would not conflict:

x

  Variable x.

x[`i`]

  Element `i` of array x. `i` can range from 0 to 2047 and can also be an expression.

x(y,z)

  Call function x with parameters y and z.

### Input-output keywords

ibase, obase, and scale store a value. Typing them on a line by themselves displays their current value. More commonly, you would change their values through assignment. Letters A-F are treated as digits whose values are 10-15.

ibase = `n`

  Numbers that are input (e.g., typed) are read as base `n` (default is 10).

obase = `n`

  Numbers displayed are in base `n` (default is 10). Note: Once ibase has been changed from 10, use digit "A" to restore ibase or obase to decimal.

scale = `n`

  Display computations using `n` decimal places (default is 0, meaning that results are truncated to integers). scale is normally used only for base-10 computations.

### Statement keywords

A semicolon or a newline separates one statement from another. Curly braces are needed only when grouping multiple statements.

if (`rel-expr`) {`statements`}

  Do one or more `statements` if relational expression `rel-expr` is true; for example:

  >     if(x==y) i = i + 1.

while (`rel-expr`) {`statements`}

  Repeat one or more `statements` while `rel-expr` is true; for example:

  >     while(i>0) {p = p*n; q = a/b; i = i-1}

for (`expr1`;`rel-expr`;`expr2`) {`statements`}

  Similar to while; for example, to print the first 10 multiples of 5, you could type:

  >     for(i=1; i<=10; i++) i*5

break

  Terminate a while or for statement.

### Function keywords

define `j`(`k`) {

  Begin the definition of function `j` having a single argument `k`. Additional arguments are allowed, separated by commas. Statements follow on successive lines. End with a }.

auto `x`, `y`

  Set up `x` and `y` as variables local to a function definition, initialized to 0 and meaningless outside the function. Must appear first.

return(`expr`)

  Pass the value of expression `expr` back to the program. Return 0 if (`expr`) is left off. Used in function definitions.

sqrt(`expr`)

  Compute the square root of expression `expr`.

length(`expr`)

  Compute how many digits are in `expr`.

scale(`expr`)

  Same, but count only digits to the right of the decimal point.

### Math library functions

These are available when bc is invoked with -l. Library functions set scale to 20.

s(`angle`)

  Compute the sine of `angle`, a constant or expression in radians.

c(`angle`)

  Compute the cosine of `angle`, a constant or expression in radians.

a(`n`)

  Compute the arctangent of `n`, returning an angle in radians.

e(`expr`)

  Compute e to the power of `expr`.

l(`expr`)

  Compute natural log of `expr`.

j(`n`, `x`)

  Compute Bessel function of integer order `n`.

### Operators

These consist of operators and other symbols. Operators can be arithmetic, unary, assignment, or relational.

arithmetic

  + `-` `*` / % ^

unary

  `-` ++ --

assignment

  =+ =`-` =* =/ =% =^ =

relational

  < <= > >= == !=

### Other symbols

/* */

  Enclose comments.

( )

  Control the evaluation of expressions (change precedence). Can also be used around assignment statements to force the result to print.

{ }

  Used to group statements.

[ ]

  Array index.

"`text`"

  Use as a statement to print `text`.

### Examples

Note below that when you type some quantity (a number or expression), it is evaluated and printed, but assignment statements produce no display.

>     ibase = 8	Octal input.
>     20		Evaluate this octal number.
>     16		Terminal displays decimal value.
>     obase = 2	Display output in base 2 instead of base 10.
>     20		Octal input.
>     10000	Terminal now displays binary value.
>     ibase = A	Restore base 10 input.
>     scale = 3	Truncate results to 3 places.
>     8/7		Evaluate a division.
>     1.001001000	Oops!  Forgot to reset output base to 10.
>     obase=10	Input is decimal now, so "A" isn't needed.
>     8/7
>     1.142	Terminal displays result (truncated).

The following lines show the use of functions:

>     define p(r,n){    Function p uses two arguments.
>       auto v          v is a local variable.
>       v = r^n         r raised to the n power.
>       return(v)}      Value returned.

>     scale=5
>     x=p(2.5,2)        x = 2.5 ^ 2
>     x                 Print value of x.
>     6.25
>     length(x)         Number of digits.
>     3
>     scale(x)          Number of places right of decimal point.
>     2

Reference: batch |  | Reference: bdiff