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Man Pages


Manual Reference Pages  -  BC (1)

NAME

bc - arbitrary-precision arithmetic language and calculator

CONTENTS

Synopsis
Description
Command Line Editing
Files
Compatibility
See Also
Standards
History
Authors
Bugs

SYNOPSIS

bc [-chlv] [-e expression] [file ...]

DESCRIPTION

bc is an interactive processor for a language which resembles C but provides unlimited precision arithmetic. It takes input from any expressions on the command line and any files given, then reads the standard input.

Options available:
-c bc is actually a preprocessor for dc(1), which it invokes automatically, unless the -c (compile only) option is present. In this case the generated dc(1) instructions are sent to the standard output, instead of being interpreted by a running dc(1) process.
-e expression,-expression expression
  Evaluate expression. If multiple -e options are specified, they are processed in the order given, separated by newlines.
-h -, -help
  Prints usage information.
-l -, -mathlib
  Allow specification of an arbitrary precision math library. The definitions in the library are available to command line expressions.
-v -, -version
  Prints version information.

The syntax for bc programs is as follows: 'L' means letter a-z; 'E' means expression; 'S' means statement. As a non-portable extension, it is possible to use long names in addition to single letter names. A long name is a sequence starting with a lowercase letter followed by any number of lowercase letters and digits. The underscore character ('_') counts as a letter.

Comments

are enclosed in /* and */
are enclosed in # and the next newline

The newline is not part of the line comment, which in itself is a non-portable extension.

Names

simple variables: L
array elements: L [ E ]
The words ‘ibase’, ‘obase’, and ‘scale’
The word ‘last’ or a single dot

Other operands

arbitrarily long numbers with optional sign and decimal point
( E )
sqrt ( E )
length ( E )    number of significant decimal digits
scale ( E )     number of digits right of decimal point
L ( E , ... , E )

The sequence '\<newline><whitespace>' is ignored within numbers.

Operators

The following arithmetic and logical operators can be used. The semantics of the operators is the same as in the C language. They are listed in order of decreasing precedence. Operators in the same group have the same precedence.
Operator      Associativity      Description
++ --      none      increment, decrement
-      none      unary minus
^      right      power
* / %      left      multiply, divide, modulus
+ -      left      plus, minus
= += -= *= /= %= ^=      right      assignment
== <= >= != < >      none      relational
!      none      boolean not
&&      left      boolean and
||      left      boolean or
 

Note the following:

  • The relational operators may appear in any expression. The -p1003.1-2008 standard only allows them in the conditional expression of an 'if', 'while' or 'for' statement.
  • The relational operators have a lower precedence than the assignment operators. This has the consequence that the expression a = b < c is interpreted as (a = b) < c, which is probably not what the programmer intended.
  • In contrast with the C language, the relational operators all have the same precedence, and are non-associative. The expression a < b < c will produce a syntax error.
  • The boolean operators (!, && and ||) are non-portable extensions.
  • The boolean not (!) operator has much lower precedence than the same operator in the C language. This has the consequence that the expression !a < b is interpreted as !(a < b). Prudent programmers use parentheses when writing expressions involving boolean operators.

Statements

E
{ S ; ... ; S }
if ( E ) S
if ( E ) S else S
while ( E ) S
for ( E ; E ; E ) S
null statement
break
continue
quit
a string of characters, enclosed in double quotes
print E ,..., E

A string may contain any character, except double quote. The if statement with an else branch is a non-portable extension. All three E’s in a for statement may be empty. This is a non-portable extension. The continue and print statements are also non-portable extensions.

The print statement takes a list of comma-separated expressions. Each expression in the list is evaluated and the computed value is printed and assigned to the variable ‘last’. No trailing newline is printed. The expression may also be a string enclosed in double quotes. Within these strings the following escape sequences may be used: '\a' for bell (alert), '\b' for backspace, '\f' for formfeed, '\n' for newline, '\r' for carriage return, '\t' for tab, '\q' for double quote and '\\' for backslash. Any other character following a backslash will be ignored. Strings will not be assigned to ‘last’.

Function definitions

define L ( L ,..., L ) {
        auto L, ... , L
        S; ... S
        return ( E )
}

As a non-portable extension, the opening brace of the define statement may appear on the next line. The return statement may also appear in the following forms:

return
return ()
return E

The first two are equivalent to the statement "return 0". The last form is a non-portable extension. Not specifying a return statement is equivalent to writing "return (0)".

Functions available in the math library, which is loaded by specifying the -l flag on the command line

s(x) sine
c(x) cosine
e(x) exponential
l(x) log
a(x) arctangent
j(n,x) Bessel function

All function arguments are passed by value.

The value of a statement that is an expression is printed unless the main operator is an assignment. The value printed is assigned to the special variable ‘last’. This is a non-portable extension. A single dot may be used as a synonym for ‘last’. Either semicolons or newlines may separate statements. Assignment to scale influences the number of digits to be retained on arithmetic operations in the manner of dc(1). Assignments to ibase or obase set the input and output number radix respectively.

The same letter may be used as an array, a function, and a simple variable simultaneously. All variables are global to the program. ‘Auto’ variables are pushed down during function calls. When using arrays as function arguments or defining them as automatic variables, empty square brackets must follow the array name.

For example

scale = 20
define e(x){
        auto a, b, c, i, s
        a = 1
        b = 1
        s = 1
        for(i=1; 1==1; i++){
                a = a*x
                b = b*i
                c = a/b
                if(c == 0) return(s)
                s = s+c
        }
}

defines a function to compute an approximate value of the exponential function and

    for(i=1; i<=10; i++) e(i)

prints approximate values of the exponential function of the first ten integers.

$ bc -l -e ’scale = 500; 2 * a(2^10000)’ -e quit

prints an approximation of pi.

COMMAND LINE EDITING

bc supports interactive command line editing, via the editline(3) library. It is enabled by default if input is from a tty. Previous lines can be recalled and edited with the arrow keys, and other GNU Emacs-style editing keys may be used as well.

The editline(3) library is configured with a .editrc file - refer to editrc(5) for more information.

FILES

/usr/share/misc/bc.library
  math library, read when the -l option is specified on the command line.

COMPATIBILITY

The -q and -quiet options are no-ops for compatibility with some other implementations of bc and their use is discouraged.

SEE ALSO

dc(1)

STANDARDS

The bc utility is compliant with the -p1003.1-2008 specification.

The flags [-ce], as well as the parts noted above, are extensions to that specification.

HISTORY

The bc command first appeared in AT&T v6 . A complete rewrite of the bc command first appeared in
.Ox 3.5 .

AUTHORS


.An -nosplit The original version of the bc command was written by
.An Robert Morris and
.An Lorinda Cherry . The current version of the bc utility was written by
.An Otto Moerbeek .

BUGS

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

Some non-portable extensions, as found in the GNU version of the bc utility are not implemented (yet).

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