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bc - Provides a processor for arbitrary-precision arithmetic language  


bc [-cl] [file...]

The bc command is an interactive program that provides unlimited precision arithmetic. It is a preprocessor for the dc command.


Interfaces documented on this reference page conform to industry standards as follows:

bc:  XPG4, XPG4-UNIX

Refer to the standards(5) reference page for more information about industry standards and associated tags.


[Compaq]  Compiles file, but does not invoke dc. Includes a library of mathematical functions. Also sets the number of digits retained after the decimal point (the scale) to 20; by default the scale is 0.


Pathname of a text file containing program statements. After file has been exhausted, standard input is read.


[Compaq]  The bc command invokes dc automatically, unless the -c (compile only) option is specified. If the -c option is specified, the output from bc goes to the standard output.

The bc command lets you specify an input and output base in decimal, octal, or hexadecimal (the default is decimal). The command also has a scaling provision for decimal point notation. The syntax for bc is similar to that of the C language.

The bc command takes input first from the specified file. When bc reaches the end of the input file, it reads standard input.

In the following description of syntax for bc, letter means one of the letters a-z.


Comments are enclosed in /* and */.


Simple variables: letter

Array elements: letter[expression]

The words ibase, obase, and scale

Other Operands

Arbitrarily long numbers with optional sign and decimal point. Number of significant decimal digits Number of digits to right of decimal point


+ - * / % ^ (% is remainder; ^ is power)

++ -- (prefix and suffix; apply to names)

== <= >= != <>

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

+= -= *= /= %=




if (expression) statement

while (expression) statement

for (expression;expression;expression) statement

(null statement)



Function Definitions

define letter ( letter,...,letter ) {

       auto letter,...,letter
       return ( expression ) }


Functions in -l Math Library

sine cosine exponential log arctangent Bessel function

General Syntax

All function parameters are passed by value.

The value of a statement that is an expression is displayed, unless the main operator is an assignment. A semicolon or newline character separates statements. Assignments to scale control the number of decimal places printed on output and maintained during multiplication, division, and exponentiation. Assignments to ibase or obase set the input and output number radix, respectively.

The same letter may refer to an array, a function, and a simple variable simultaneously. All variables are global to the program. Automatic variables are pushed down during function calls. When you use arrays as function parameters, or define them as automatic variables, empty brackets must follow the array name.

All for statements must have all three expressions.

The quit statement is interpreted when read, not when executed.


The following exit values are returned: Successful completion. An error occurred.


When you enter bc expressions directly from the keyboard, press the End-of-File key sequence to end the bc session and return to the shell command line. To use bc as a calculator, proceed as follows:

Enter: $ bc 1/4
The system responds as follows: 0
Enter: scale = 1 /* Keep 1 decimal place */ 1/4
The system responds as follows: 0.2
Enter: scale = 3 /* Keep 3 decimal places */ 1/4
The system responds as follows: 0.250
Enter: 16+63/5
The system responds as follows: 28.600
Enter: (16+63)/5
The system responds as follows: 15.800
Enter: 71/6
The system responds as follows: 11.833
Enter: 1/6
The system responds as follows: 0.166
You may type the comments (enclosed in /* */), but they are provided only for your information. The bc command displays the value of each expression when you press <Return>, except for assignments. To convert numbers from one base to another, proceed as follows:
Enter: bc obase = 16      /* Display numbers in Hexadecimal */
ibase = 8               /* Input numbers in Octal       */
The system responds as follows: A
Enter: 123
The system responds as follows: 53
Enter: 123456
The system responds as follows: A72E To write and run C-like programs, proceed as follows:
Create the following file prog.bc:
/* compute the factorial of n */

  define f(n) {         auto i, r;

       r = 1;
        for (i=2; i<=n; i++) r =* i;
        return (r);


Enter: bc -l prog.bc
This interprets the bc program saved in prog.bc, then reads more bc command statements from standard input (the keyboard). Starting the bc command with the -l option makes the math library available. This example uses the e (exponential) function from the math library, and f is defined in the program prog.bc.
Enter: e(2)   /* e squared   */
The system responds as follows: 7.38905609893065022723
Enter: f(5)   /* 5 factorial */
The system responds as follows: 120
Enter: f(10)  /* 10 factorial */
The system responds as follows: 3628800
The statement following a for or while statement must begin on the same line. To convert an infix expression to Reverse Polish Notation (RPN), enter:
Enter: bc -c (a * b) % (3 + 4 * c)
The system responds as follows: lalb* 3 4lc*+%ps.
This compiles the bc infix-notation expression into one that the dc command can interpret. The dc command evaluates extended RPN expressions. In the compiled output, the lowercase l before each variable name is the dc subcommand to load the value of the variable onto the stack. The p displays the value on top of the stack, and the s. discards the top value by storing it in register . (dot). You can save the RPN expression in a file for dc to evaluate later by redirecting the standard output of this command.


The following environment variables affect the execution of bc: Provides a default value for the internationalization variables that are unset or null. If LANG is unset or null, the corresponding value from the default locale is used. If any of the internationalization variables contain an invalid setting, the utility behaves as if none of the variables had been defined. If set to a non-empty string value, overrides the values of all the other internationalization variables. Determines the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multibyte characters in arguments). Determines the locale for the format and contents of diagnostic messages written to standard error. Determines the location of message catalogues for the processing of LC_MESSAGES.


Mathematical library. Desk calculator proper; uses bc as preprocessor.


Commands:  awk(1), dc(1)

Standards:  standards(5)



Other Operands
Function Definitions
Functions in -l Math Library
General Syntax

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Time: 02:42:49 GMT, October 02, 2010