path: root/usr.bin/bc/bc.1

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.\"	@(#)bc.1	6.8 (Berkeley) 8/8/91
.\"
.Dd $Mdocdate: July 16 2009 $
.Dt BC 1
.Sh NAME
.Nm bc
.Nd arbitrary-precision arithmetic language and calculator
.Sh SYNOPSIS
.Nm bc
.Op Fl cl
.Op Fl e Ar expression
.Op Ar file ...
.Sh DESCRIPTION
.Nm
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.
.Pp
Options available:
.Bl -tag -width Ds
.It Fl c
.Nm
is actually a preprocessor for
.Xr dc 1 ,
which it invokes automatically, unless the
.Fl c
.Pq compile only
option is present.
In this case the generated
.Xr dc 1
instructions are sent to the standard output,
instead of being interpreted by a running
.Xr dc 1
process.
.It Fl e Ar expression
Evaluate
.Ar expression .
If multiple
.Fl e
options are specified, they are processed in the order given,
separated by newlines.
.It Fl l
Allow specification of an arbitrary precision math library.
The definitions in the library are available to command line
expressions.
.El
.Pp
The syntax for
.Nm
programs is as follows:
.Sq L
means letter a-z;
.Sq E
means expression;
.Sq 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
.Pq Sq _
counts as a letter.
.Pp
Comments
.Bd -unfilled -offset indent -compact
are enclosed in /* and */
are enclosed in # and the next newline
.Ed
.Pp
The newline is not part of the line comment,
which in itself is a non-portable extension.
.Pp
Names
.Bd -unfilled -offset indent -compact
simple variables: L
array elements: L [ E ]
The words `ibase', `obase', and `scale'
The word `last' or a single dot
.Ed
.Pp
Other operands
.Bd -unfilled -offset indent -compact
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 )
.Ed
.Pp
The sequence
.Sq \e<newline><whitespace>
is ignored within numbers.
.Pp
Operators
.Pp
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.
.Bl -column -offset indent "= += \-= *= /= %= ^=" "Associativity" \
"multiply, divide, modulus"
.It Sy "Operator" Ta Sy "Associativity" Ta Sy "Description"
.It "++ \-\-" Ta "none" Ta "increment, decrement"
.It "\-" Ta "none" Ta "unary minus"
.It "^" Ta "right" Ta "power"
.It "* / %" Ta "left" Ta "multiply, divide, modulus"
.It "+ \-" Ta "left" Ta "plus, minus"
.It "= += -= *= /= %= ^=" Ta "right" Ta "assignment"
.It "== <= >= != < >" Ta "none" Ta "relational"
.It "!" Ta "none" Ta "boolean not"
.It "&&" Ta "left" Ta "boolean and"
.It "||" Ta "left" Ta "boolean or"
.El
.Pp
Note the following:
.Bl -bullet -offset indent
.It
The relational operators may appear in any expression.
The
.St -p1003.2
standard only allows them in the conditional expression of an
.Sq if ,
.Sq while
or
.Sq for
statement.
.It
The relational operators have a lower precedence than the assignment
operators.
This has the consequence that the expression
.Sy a = b < c
is interpreted as
.Sy (a = b) < c ,
which is probably not what the programmer intended.
.It
In contrast with the C language, the relational operators all have
the same precedence, and are non-associative.
The expression
.Sy a < b < c
will produce a syntax error.
.It
The boolean operators (!, && and ||) are non-portable extensions.
.It
The boolean not
(!) operator has much lower precedence than the same operator in the
C language.
This has the consequence that the expression
.Sy !a < b
is interpreted as
.Sy !(a < b) .
Prudent programmers use parentheses when writing expressions involving
boolean operators.
.El
.Pp
Statements
.Bd -unfilled -offset indent -compact
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
.Ed
.Pp
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.
.Pp
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:
.Sq \ea
for bell (alert),
.Sq \eb
for backspace,
.Sq \ef
for formfeed,
.Sq \en
for newline,
.Sq \er
for carriage return,
.Sq \et
for tab,
.Sq \eq
for double quote and
.Sq \e\e
for backslash.
Any other character following a backslash will be ignored.
Strings will not be assigned to `last'.
.Pp
Function definitions
.Bd -unfilled -offset indent
define L ( L ,..., L ) {
	auto L, ... , L
	S; ... S
	return ( E )
}
.Ed
.Pp
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:
.Bd -unfilled -offset indent
return
return ()
return E
.Ed
.Pp
The first two are equivalent to the statement
.Dq return 0 .
The last form is a non-portable extension.
Not specifying a return statement is equivalent to writing
.Dq return (0) .
.Pp
Functions available in the math library, which is loaded by specifying the
.Fl l
flag on the command line
.Pp
.Bl -tag -width j(n,x) -offset indent -compact
.It s(x)
sine
.It c(x)
cosine
.It e(x)
exponential
.It l(x)
log
.It a(x)
arctangent
.It j(n,x)
Bessel function
.El
.Pp
All function arguments are passed by value.
.Pp
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
.Ar scale
influences the number of digits to be retained on arithmetic
operations in the manner of
.Xr dc 1 .
Assignments to
.Ar ibase
or
.Ar obase
set the input and output number radix respectively.
.Pp
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.
.Pp
For example
.Bd -literal -offset indent
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
	}
}
.Ed
.Pp
defines a function to compute an approximate value of
the exponential function and
.Pp
.Dl for(i=1; i<=10; i++) e(i)
.Pp
prints approximate values of the exponential function of
the first ten integers.
.Bd -literal -offset indent
$ bc -l -e 'scale = 500; 2 * a(2^10000)' -e quit
.Ed
.Pp
prints an approximation of pi.
.Sh FILES
.Bl -tag -width /usr/share/misc/bc.library -compact
.It Pa /usr/share/misc/bc.library
math library, read when the
.Fl l
option is specified on the command line.
.El
.Sh SEE ALSO
.Xr dc 1
.Pp
"BC \- An Arbitrary Precision Desk-Calculator Language",
.Pa /usr/share/doc/usd/06.bc/ .
.Sh STANDARDS
The
.Nm
utility is compliant with the
.St -p1003.1-2008
specification.
.Pp
The flags
.Op Fl ce
are extensions to that specification.
.Sh HISTORY
The
.Nm
command first appeared in
.At v6 .
A complete rewrite of the
.Nm
command first appeared in
.Ox 3.5 .
.Sh AUTHORS
.An -nosplit
The original version of the
.Nm
command was written by
.An Robert Morris
and
.An Lorinda Cherry .
The current version of the
.Nm
utility was written by
.An Otto Moerbeek .
.Sh BUGS
.Ql Quit
is interpreted when read, not when executed.
.Pp
Some non-portable extensions, as found in the GNU version of the
.Nm
utility are not implemented (yet).