bc man page on Archlinux

Man page or keyword search:  
man Server   11224 pages
apropos Keyword Search (all sections)
Output format
Archlinux logo
[printable version]

BC(1P)			   POSIX Programmer's Manual			BC(1P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       bc — arbitrary-precision arithmetic language

       bc [−l] [file...]

       The bc utility shall implement an arbitrary  precision  calculator.  It
       shall  take  input  from	 any  files given, then read from the standard
       input. If the standard input and standard output to bc are attached  to
       a terminal, the invocation of bc shall be considered to be interactive,
       causing behavioral constraints described in the following sections.

       The bc  utility	shall  conform	to  the	 Base  Definitions  volume  of
       POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.

       The following option shall be supported:

       −l	 (The  letter  ell.)  Define the math functions and initialize
		 scale to 20, instead of the default zero;  see	 the  EXTENDED
		 DESCRIPTION section.

       The following operand shall be supported:

       file	 A  pathname  of a text file containing bc program statements.
		 After all files have been read, bc shall  read	 the  standard

       See the INPUT FILES section.

       Input  files  shall  be	text  files containing a sequence of comments,
       statements, and function definitions that shall be executed as they are

       The following environment variables shall affect the execution of bc:

       LANG	 Provide  a  default  value for the internationalization vari‐
		 ables that are unset or null. (See the Base Definitions  vol‐
		 ume  of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
		 ables for the precedence  of  internationalization  variables
		 used to determine the values of locale categories.)

       LC_ALL	 If  set  to  a non-empty string value, override the values of
		 all the other internationalization variables.

       LC_CTYPE	 Determine the locale for the interpretation of	 sequences  of
		 bytes of text data as characters (for example, single-byte as
		 opposed to  multi-byte	 characters  in	 arguments  and	 input

		 Determine the locale that should be used to affect the format
		 and contents  of  diagnostic  messages	 written  to  standard

       NLSPATH	 Determine the location of message catalogs for the processing


       The output of the bc utility shall be controlled by the	program	 read,
       and  consist of zero or more lines containing the value of all executed
       expressions without assignments. The radix and precision of the	output
       shall be controlled by the values of the obase and scale variables; see
       the EXTENDED DESCRIPTION section.

       The standard error shall be used only for diagnostic messages.


       The grammar in this section and the lexical conventions in the  follow‐
       ing  section  shall  together  describe the syntax for bc programs. The
       general conventions for this style of grammar are described in  Section
       1.3,  Grammar  Conventions.   A valid program can be represented as the
       non-terminal symbol program in the grammar. This	 formal	 syntax	 shall
       take precedence over the text syntax description.


	   %token    MUL_OP
	   /*	     '*', '/', '%'			     */

	   %token    ASSIGN_OP
	   /*	     '=', '+=', '−=', '*=', '/=', '%=', '^=' */

	   %token    REL_OP
	   /*	     '==', '<=', '>=', '!=', '<', '>'	     */

	   %token    INCR_DECR
	   /*	     '++', '−−'				     */

	   %token    Define    Break	Quit	Length
	   /*	     'define', 'break', 'quit', 'length'     */

	   %token    Return    For    If    While    Sqrt
	   /*	     'return', 'for', 'if', 'while', 'sqrt'  */

	   %token    Scale    Ibase    Obase	Auto
	   /*	     'scale', 'ibase', 'obase', 'auto'	     */

	   %start    program


	   program		: EOF
				| input_item program

	   input_item		: semicolon_list NEWLINE
				| function

	   semicolon_list	: /* empty */
				| statement
				| semicolon_list ';' statement
				| semicolon_list ';'

	   statement_list	: /* empty */
				| statement
				| statement_list NEWLINE
				| statement_list NEWLINE statement
				| statement_list ';'
				| statement_list ';' statement

	   statement		: expression
				| STRING
				| Break
				| Quit
				| Return
				| Return '(' return_expression ')'
				| For '(' expression ';'
				      relational_expression ';'
				      expression ')' statement
				| If '(' relational_expression ')' statement
				| While '(' relational_expression ')' statement
				| '{' statement_list '}'

	   function		: Define LETTER '(' opt_parameter_list ')'
				      '{' NEWLINE opt_auto_define_list
				      statement_list '}'

	   opt_parameter_list	: /* empty */
				| parameter_list

	   parameter_list	: LETTER
				| define_list ',' LETTER

	   opt_auto_define_list : /* empty */
				| Auto define_list NEWLINE
				| Auto define_list ';'

	   define_list		: LETTER
				| LETTER '[' ']'
				| define_list ',' LETTER
				| define_list ',' LETTER '[' ']'

	   opt_argument_list	: /* empty */
				| argument_list

	   argument_list	: expression
				| LETTER '[' ']' ',' argument_list

	   relational_expression : expression
				| expression REL_OP expression

	   return_expression	: /* empty */
				| expression

	   expression		: named_expression
				| NUMBER
				| '(' expression ')'
				| LETTER '(' opt_argument_list ')'
				| '−' expression
				| expression '+' expression
				| expression '−' expression
				| expression MUL_OP expression
				| expression '^' expression
				| INCR_DECR named_expression
				| named_expression INCR_DECR
				| named_expression ASSIGN_OP expression
				| Length '(' expression ')'
				| Sqrt '(' expression ')'
				| Scale '(' expression ')'

	   named_expression	: LETTER
				| LETTER '[' expression ']'
				| Scale
				| Ibase
				| Obase

   Lexical Conventions in bc
       The  lexical conventions for bc programs, with respect to the preceding
       grammar, shall be as follows:

	1. Except as noted, bc shall recognize the longest possible  token  or
	   delimiter beginning at a given point.

	2. A  comment  shall  consist of any characters beginning with the two
	   adjacent characters "/*" and terminated by the next	occurrence  of
	   the	two  adjacent  characters "*/".	 Comments shall have no effect
	   except to delimit lexical tokens.

	3. The <newline> shall be recognized as the token NEWLINE.

	4. The token STRING shall represent a string constant; it  shall  con‐
	   sist	 of  any  characters beginning with the double-quote character
	   ('"') and terminated by  another  occurrence	 of  the  double-quote
	   character.  The  value of the string is the sequence of all charac‐
	   ters between, but not including, the two  double-quote  characters.
	   All	characters  shall be taken literally from the input, and there
	   is no way to specify a string containing a double-quote  character.
	   The	length	of  the	 value	of  each  string  shall	 be limited to
	   {BC_STRING_MAX} bytes.

	5. A <blank> shall have no effect except as an ordinary	 character  if
	   it  appears	within	a  STRING token, or to delimit a lexical token
	   other than STRING.

	6. The combination of a <backslash> character immediately followed  by
	   a  <newline>	 shall	have  no  effect other than to delimit lexical
	   tokens with the following exceptions:

	    *  It shall be interpreted as the character sequence  "\<newline>"
	       in STRING tokens.

	    *  It shall be ignored as part of a multi-line NUMBER token.

	7. The	token  NUMBER  shall represent a numeric constant. It shall be
	   recognized by the following grammar:

	       NUMBER  : integer
		       | '.' integer
		       | integer '.'
		       | integer '.' integer

	       integer : digit
		       | integer digit

	       digit   : 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7
		       | 8 | 9 | A | B | C | D | E | F

	8. The value of a NUMBER token shall be interpreted as	a  numeral  in
	   the	base  specified	 by  the  value of the internal register ibase
	   (described below). Each of the  digit  characters  shall  have  the
	   value from 0 to 15 in the order listed here, and the <period> char‐
	   acter shall represent the radix point. The behavior is undefined if
	   digits  greater  than  or equal to the value of ibase appear in the
	   token. However, note the exception for  single-digit	 values	 being
	   assigned to ibase and obase themselves, in Operations in bc.

	9. The following keywords shall be recognized as tokens:

	   auto	    ibase    length   return   while
	   break    if	     obase    scale
	   define   for	     quit     sqrt

       10. Any	of the following characters occurring anywhere except within a
	   keyword shall be recognized as the token LETTER:

	       a b c d e f g h i j k l m n o p q r s t u v w x y z

       11. The following single-character and two-character sequences shall be
	   recognized as the token ASSIGN_OP:

	       =   +=	−=   *=	  /=   %=   ^=

       12. If  an '=' character, as the beginning of a token, is followed by a
	   '−' character with no intervening delimiter, the behavior is	 unde‐

       13. The	following  single-characters  shall be recognized as the token

	       *   /   %

       14. The following single-character and two-character sequences shall be
	   recognized as the token REL_OP:

	       ==   <=	 >=   !=   <   >

       15. The	following  two-character  sequences shall be recognized as the
	   token INCR_DECR:

	       ++   −−

       16. The following single characters shall be recognized as tokens whose
	   names are the character:

	       <newline>  (  )	,  +  −	 ;  [  ]  ^  {	}

       17. The token EOF is returned when the end of input is reached.

   Operations in bc
       There are three kinds of identifiers: ordinary identifiers, array iden‐
       tifiers, and function identifiers.  All three types consist  of	single
       lowercase letters. Array identifiers shall be followed by square brack‐
       ets ("[]").  An array subscript is required except in  an  argument  or
       auto  list.   Arrays  are  singly  dimensioned  and  can	 contain up to
       {BC_DIM_MAX} elements. Indexing shall begin at  zero  so	 an  array  is
       indexed	from  0	 to  {BC_DIM_MAX}−1.  Subscripts shall be truncated to
       integers. The application shall ensure that  function  identifiers  are
       followed	 by parentheses, possibly enclosing arguments. The three types
       of identifiers do not conflict.

       The following table summarizes the rules for precedence and associativ‐
       ity  of	all  operators. Operators on the same line shall have the same
       precedence; rows are in order of decreasing precedence.

			       Table: Operators in bc

		     │	      Operator		│ Associativity │
		     │++, −−			│ N/A		│
		     │unary −			│ N/A		│
		     │^				│ Right to left │
		     │*, /, %			│ Left to right │
		     │+, binary −		│ Left to right │
		     │=, +=, −=, *=, /=, %=, ^= │ Right to left │
		     │==, <=, >=, !=, <, >	│ None		│
       Each expression or named expression has a scale, which is the number of
       decimal	digits	that  shall be maintained as the fractional portion of
       the expression.

       Named expressions are places where values are stored. Named expressions
       shall  be valid on the left side of an assignment. The value of a named
       expression shall be the value stored in the place named. Simple identi‐
       fiers  and  array  elements are named expressions; they have an initial
       value of zero and an initial scale of zero.

       The internal registers scale, ibase, and obase are  all	named  expres‐
       sions.  The  scale  of  an  expression consisting of the name of one of
       these registers shall be zero; values assigned to any of	 these	regis‐
       ters  are  truncated  to	 integers.  The scale register shall contain a
       global value used in computing the scale of expressions	(as  described
       below).	The  value  of	the  register  scale is limited to 0 ≤ scale ≤
       {BC_SCALE_MAX} and shall have a default value of zero.  The  ibase  and
       obase  registers	 are  the input and output number radix, respectively.
       The value of ibase shall be limited to:

	   2 ≤ ibase ≤ 16

       The value of obase shall be limited to:

	   2 ≤ obase ≤ {BC_BASE_MAX}

       When either ibase or obase is assigned a single digit  value  from  the
       list  in Lexical Conventions in bc, the value shall be assumed in hexa‐
       decimal. (For example, ibase=A sets to base ten, regardless of the cur‐
       rent  ibase  value.)  Otherwise,	 the behavior is undefined when digits
       greater than or equal to the value of ibase appear in the  input.  Both
       ibase and obase shall have initial values of 10.

       Internal	 computations  shall be conducted as if in decimal, regardless
       of the input and output bases, to the specified number of decimal  dig‐
       its.   When   an	  exact	  result   is	not   achieved	(for  example,
       scale=0; 3.2/1), the result shall be truncated.

       For all values of obase specified by this volume	 of  POSIX.1‐2008,  bc
       shall  output  numeric values by performing each of the following steps
       in order:

	1. If the value is less than zero, a <hyphen> ('−') character shall be

	2. One of the following is output, depending on the numerical value:

	    *  If the absolute value of the numerical value is greater than or
	       equal to one, the integer portion of the value shall be	output
	       as  a  series  of  digits  appropriate  to  obase (as described
	       below), most significant digit first. The most significant non-
	       zero  digit shall be output next, followed by each successively
	       less significant digit.

	    *  If the absolute value of the numerical value is less  than  one
	       but  greater  than zero and the scale of the numerical value is
	       greater than zero, it is unspecified whether the character 0 is

	    *  If  the	numerical value is zero, the character 0 shall be out‐

	3. If the scale of the value is greater	 than  zero  and  the  numeric
	   value  is  not zero, a <period> character shall be output, followed
	   by a series of digits appropriate to	 obase	(as  described	below)
	   representing the most significant portion of the fractional part of
	   the value. If s represents the scale of the value being output, the
	   number  of  digits  output  shall be s if obase is 10, less than or
	   equal to s if obase is greater than 10, or greater than or equal to
	   s  if  obase	 is less than 10. For obase values other than 10, this
	   should be the number of digits needed to represent a	 precision  of

       For  obase values from 2 to 16, valid digits are the first obase of the
       single characters:

	   0  1	 2  3  4  5  6	7  8  9	 A  B  C  D  E	F

       which represent the values zero to 15, inclusive, respectively.

       For bases greater than 16, each digit shall be written  as  a  separate
       multi-digit  decimal  number.  Each  digit  except the most significant
       fractional digit shall be preceded by a single <space>.	For bases from
       17 to 100, bc shall write two-digit decimal numbers; for bases from 101
       to 1000, three-digit decimal strings, and so on. For example, the deci‐
       mal number 1024 in base 25 would be written as:

	    01 15 24

       and in base 125, as:

	    008 024

       Very  large  numbers shall be split across lines with 70 characters per
       line in the POSIX locale; other locales may split at different  charac‐
       ter boundaries. Lines that are continued shall end with a <backslash>.

       A  function call shall consist of a function name followed by parenthe‐
       ses containing a <comma>-separated list of expressions, which  are  the
       function arguments. A whole array passed as an argument shall be speci‐
       fied by the array name followed by empty square brackets. All  function
       arguments  shall	 be  passed by value. As a result, changes made to the
       formal parameters shall have no effect on the actual arguments. If  the
       function	 terminates  by executing a return statement, the value of the
       function shall be the value of the expression in the parentheses of the
       return  statement  or  shall be zero if no expression is provided or if
       there is no return statement.

       The result of sqrt(expression) shall be the square root of the  expres‐
       sion.  The  result  shall be truncated in the least significant decimal
       place. The scale of the result shall be the scale of the expression  or
       the value of scale, whichever is larger.

       The  result of length(expression) shall be the total number of signifi‐
       cant decimal digits in the expression. The scale of the result shall be

       The  result  of scale(expression) shall be the scale of the expression.
       The scale of the result shall be zero.

       A numeric constant shall be an expression. The scale shall be the  num‐
       ber of digits that follow the radix point in the input representing the
       constant, or zero if no radix point appears.

       The sequence ( expression ) shall be an expression with the same	 value
       and scale as expression.	 The parentheses can be used to alter the nor‐
       mal precedence.

       The semantics of the unary and binary operators are as follows:

	     The result shall be the negative of the expression.  The scale of
	     the result shall be the scale of expression.

       The  unary increment and decrement operators shall not modify the scale
       of the named expression upon which  they	 operate.  The	scale  of  the
       result shall be the scale of that named expression.

	     The  named	 expression  shall  be	incremented by one. The result
	     shall be the value of the named expression after incrementing.

	     The named expression shall be  decremented	 by  one.  The	result
	     shall be the value of the named expression after decrementing.

	     The  named	 expression  shall  be	incremented by one. The result
	     shall be the value of the named expression before incrementing.

	     The named expression shall be  decremented	 by  one.  The	result
	     shall be the value of the named expression before decrementing.

       The  exponentiation  operator,  <circumflex> ('^'), shall bind right to

	     The result shall be the first expression raised to the  power  of
	     the  second expression.  If the second expression is not an inte‐
	     ger, the behavior is undefined.  If a is the scale	 of  the  left
	     expression	 and  b is the absolute value of the right expression,
	     the scale of the result shall be:

		 if b >= 0 min(a * b, max(scale, a)) if b < 0 scale

       The multiplicative operators ('*', '/', '%') shall bind left to right.

	     The result shall be the product of the two expressions. If a  and
	     b	are  the  scales of the two expressions, then the scale of the
	     result shall be:


	     The result shall be the quotient  of  the	two  expressions.  The
	     scale of the result shall be the value of scale.

	     For expressions a and b, a%b shall be evaluated equivalent to the

	      1. Compute a/b to current scale.

	      2. Use the result to compute:

		     a − (a / b) * b

		 to scale:

		     max(scale + scale(b), scale(a))

	     The scale of the result shall be:

		 max(scale + scale(b), scale(a))

	     When scale is zero, the '%' operator is the mathematical  remain‐
	     der operator.

       The additive operators ('+', '−') shall bind left to right.

	     The  result shall be the sum of the two expressions. The scale of
	     the result shall be the maximum of the scales of the expressions.

	     The result shall be the difference of the	two  expressions.  The
	     scale  of	the  result  shall be the maximum of the scales of the

       The assignment operators ('=', "+=",  "−=",  "*=",  "/=",  "%=",	 "^=")
       shall bind right to left.

	     This  expression  shall  result  in  assigning  the  value of the
	     expression on the right to the named expression on the left.  The
	     scale  of	both  the named expression and the result shall be the
	     scale of expression.

       The compound assignment forms:

	   named-expression <operator>= expression

       shall be equivalent to:

	   named-expression=named-expression <operator> expression

       except that the named-expression shall be evaluated only once.

       Unlike all other operators, the relational operators ('<',  '>',	 "<=",
       ">=", "==", "!=") shall be only valid as the object of an if, while, or
       inside a for statement.

	     The relation shall	 be  true  if  the  value  of  expression1  is
	     strictly less than the value of expression2.

	     The  relation  shall  be  true  if	 the  value  of expression1 is
	     strictly greater than the value of expression2.

	     The relation shall be true if the value of	 expression1  is  less
	     than or equal to the value of expression2.

	     The relation shall be true if the value of expression1 is greater
	     than or equal to the value of expression2.

	     The relation shall be true	 if  the  values  of  expression1  and
	     expression2 are equal.

	     The  relation  shall  be  true  if	 the values of expression1 and
	     expression2 are unequal.

       There are only two storage classes in bc: global and automatic (local).
       Only identifiers that are local to a function need be declared with the
       auto command. The arguments to a function shall be local to  the	 func‐
       tion.   All other identifiers are assumed to be global and available to
       all functions. All identifiers, global and local, have  initial	values
       of  zero.  Identifiers  declared as auto shall be allocated on entry to
       the function and released on returning from the function.  They	there‐
       fore  do not retain values between function calls. Auto arrays shall be
       specified by the array name followed by empty square brackets. On entry
       to  a  function,	 the old values of the names that appear as parameters
       and as automatic variables shall be pushed  onto	 a  stack.  Until  the
       function	 returns, reference to these names shall refer only to the new

       References to any of these names from other functions that  are	called
       from this function also refer to the new value until one of those func‐
       tions uses the same name for a local variable.

       When a statement is an expression,  unless  the	main  operator	is  an
       assignment,  execution  of  the	statement shall write the value of the
       expression followed by a <newline>.

       When a statement is a string, execution of the  statement  shall	 write
       the value of the string.

       Statements  separated  by  <semicolon> or <newline> characters shall be
       executed sequentially. In an interactive invocation of bc, each time  a
       <newline> is read that satisfies the grammatical production:

	   input_item : semicolon_list NEWLINE

       the sequential list of statements making up the semicolon_list shall be
       executed immediately and any output produced by that execution shall be
       written without any delay due to buffering.

       In  an  if  statement  (if(relation) statement), the statement shall be
       executed if the relation is true.

       The while statement (while(relation) statement) implements  a  loop  in
       which  the  relation  is	 tested;  each	time the relation is true, the
       statement shall be executed and the relation retested. When  the	 rela‐
       tion is false, execution shall resume after statement.

       A  for statement(for(expression; relation; expression) statement) shall
       be the same as:

	   while (relation) {

       The application shall ensure that all three expressions are present.

       The break statement shall cause termination of a for  or	 while	state‐

       The  auto statement (auto identifier [,identifier] ...) shall cause the
       values of the identifiers to be pushed down.  The  identifiers  can  be
       ordinary	 identifiers  or array identifiers. Array identifiers shall be
       specified by following the array name by	 empty	square	brackets.  The
       application shall ensure that the auto statement is the first statement
       in a function definition.

       A define statement:

	   define LETTER ( opt_parameter_list ) {

       defines a function named LETTER.	 If a function named LETTER was previ‐
       ously  defined, the define statement shall replace the previous defini‐
       tion. The expression:

	   LETTER ( opt_argument_list )

       shall invoke the function named LETTER.	The behavior is	 undefined  if
       the  number of arguments in the invocation does not match the number of
       parameters in the definition. Functions shall be	 defined  before  they
       are  invoked.  A	 function shall be considered to be defined within its
       own body, so recursive calls are valid. The values of numeric constants
       within  a  function  shall  be interpreted in the base specified by the
       value of the ibase register when the function is invoked.

       The return statements (return and return(expression)) shall cause  ter‐
       mination	 of  a function, popping of its auto variables, and specifica‐
       tion of the result of the function. The first form shall be  equivalent
       to  return(0).  The value and scale of the result returned by the func‐
       tion shall be the value and scale of the expression returned.

       The quit statement (quit) shall stop execution of a bc program  at  the
       point  where  the statement occurs in the input, even if it occurs in a
       function definition, or in an if, for, or while statement.

       The following functions shall be defined when the −l option  is	speci‐

       s( expression )
	     Sine of argument in radians.

       c( expression )
	     Cosine of argument in radians.

       a( expression )
	     Arctangent of argument.

       l( expression )
	     Natural logarithm of argument.

       e( expression )
	     Exponential function of argument.

       j( expression, expression )
	     Bessel function of integer order.

       The  scale of the result returned by these functions shall be the value
       of the scale register at the time the function is invoked. The value of
       the scale register after these functions have completed their execution
       shall be the same value it had upon invocation. The behavior  is	 unde‐
       fined if any of these functions is invoked with an argument outside the
       domain of the mathematical function.

       The following exit values shall be returned:

       0	 All input files were processed successfully.

		 An error occurred.

       If any file operand is specified and the named file cannot be accessed,
       bc  shall  write	 a  diagnostic message to standard error and terminate
       without any further action.

       In an interactive invocation of bc, the utility should print  an	 error
       message and recover following any error in the input. In a non-interac‐
       tive invocation of bc, invalid input causes undefined behavior.

       The following sections are informative.

       Automatic variables in bc do not work in exactly the  same  way	as  in
       either C or PL/1.

       For  historical	reasons, the exit status from bc cannot be relied upon
       to indicate that an error has occurred.	Returning zero after an	 error
       is  possible.  Therefore,  bc  should  be used primarily by interactive
       users (who can react to error messages) or by application programs that
       can  somehow  validate the answers returned as not including error mes‐

       The bc utility always uses the <period> ('.')  character to represent a
       radix  point,  regardless  of  any decimal-point character specified as
       part of the current locale. In languages like C or  awk,	 the  <period>
       character  is  used  in program source, so it can be portable and unam‐
       biguous, while the locale-specific character is used in input and  out‐
       put.  Because  there  is no distinction between source and input in bc,
       this arrangement would not be possible. Using the locale-specific char‐
       acter in bc's input would introduce ambiguities into the language; con‐
       sider the following example in a locale with a <comma> as the  decimal-
       point character:

	   define f(a,b) {


       Because	of  such ambiguities, the <period> character is used in input.
       Having input follow different conventions from output would be  confus‐
       ing  in	either pipeline usage or interactive usage, so the <period> is
       also used in output.

       In the shell, the following assigns an approximation of the  first  ten
       digits of 'π' to the variable x:

	   x=$(printf "%s\n" 'scale = 10; 104348/33215' | bc)

       The  following  bc program prints the same approximation of 'π', with a
       label, to standard output:

	   scale = 10
	   "pi equals "
	   104348 / 33215

       The following defines a function to compute an approximate value of the
       exponential function (note that such a function is predefined if the −l
       option is specified):

	   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) {
		   s = s+c

       The following prints approximate values of the exponential function  of
       the first ten integers:

	   for (i = 1; i <= 10; ++i) {

       The bc utility is implemented historically as a front-end processor for
       dc; dc was not selected to be  part  of	this  volume  of  POSIX.1‐2008
       because bc was thought to have a more intuitive programmatic interface.
       Current implementations that implement bc using dc are expected	to  be

       The exit status for error conditions has been left unspecified for sev‐
       eral reasons:

	*  The bc utility is used in both interactive and non-interactive sit‐
	   uations.  Different exit codes may be appropriate for the two uses.

	*  It is unclear when a non-zero exit should be given; divide-by-zero,
	   undefined functions, and syntax errors are all possibilities.

	*  It is not clear what utility the exit status has.

	*  In the 4.3 BSD, System V, and  Ninth	 Edition  implementations,  bc
	   works  in conjunction with dc.  The dc utility is the parent, bc is
	   the child. This was done to cleanly terminate bc if dc aborted.

       The decision to have bc exit upon encountering  an  inaccessible	 input
       file is based on the belief that bc file1 file2 is used most often when
       at least	 file1	contains  data/function	 declarations/initializations.
       Having bc continue with prerequisite files missing is probably not use‐
       ful. There is no implication in the CONSEQUENCES OF ERRORS section that
       bc  must	 check	all  its files for accessibility before opening any of

       There was considerable debate on the appropriateness  of	 the  language
       accepted	 by bc.	 Several reviewers preferred to see either a pure sub‐
       set of the C language or some changes to make the language more compat‐
       ible with C.  While the bc language has some obvious similarities to C,
       it has never claimed to be compatible with any version of C. An	inter‐
       preter  for  a  subset  of C might be a very worthwhile utility, and it
       could potentially make bc obsolete. However, no such utility  is	 known
       in  historical practice, and it was not within the scope of this volume
       of POSIX.1‐2008 to define such a language and utility. If and when they
       are  defined, it may be appropriate to include them in a future version
       of this standard. This left the following alternatives:

	1. Exclude any calculator language from this volume of POSIX.1‐2008.

	   The consensus of the standard developers was that a simple program‐
	   matic  calculator language is very useful for both applications and
	   interactive users. The only arguments for excluding any  calculator
	   were	 that  it would become obsolete if and when a C-compatible one
	   emerged, or that the absence would  encourage  the  development  of
	   such	 a  C-compatible  one.	These  arguments  did not sufficiently
	   address the needs of current application developers.

	2. Standardize the historical dc, possibly with minor modifications.

	   The consensus of the standard developers was that dc is a fundamen‐
	   tally  less usable language and that that would be far too severe a
	   penalty for avoiding the issue of being similar to but incompatible
	   with C.

	3. Standardize the historical bc, possibly with minor modifications.

	   This was the approach taken. Most of the proponents of changing the
	   language would not have been satisfied until most  or  all  of  the
	   incompatibilities  with  C were resolved. Since most of the changes
	   considered most desirable would break historical  applications  and
	   require  significant	 modification  to  historical implementations,
	   almost no modifications were made. The one significant modification
	   that	 was  made was the replacement of the historical bc assignment
	   operators "=+", and so on, with the more modern "+=",  and  so  on.
	   The	older  versions	 are  considered  to  be  fundamentally flawed
	   because of the lexical ambiguity in uses like a=−1.

	   In order to permit implementations to deal with  backwards-compati‐
	   bility  as  they  see  fit, the behavior of this one ambiguous con‐
	   struct was made undefined. (At  least  three	 implementations  have
	   been	 known to support this change already, so the degree of change
	   involved should not be great.)

       The '%' operator is the mathematical remainder operator when  scale  is
       zero.  The  behavior of this operator for other values of scale is from
       historical implementations of bc, and has been maintained for the  sake
       of historical applications despite its non-intuitive nature.

       Historical  implementations permit setting ibase and obase to a broader
       range of values. This includes values less than 2, which were not  seen
       as  sufficiently	 useful	 to  standardize. These implementations do not
       interpret input properly for values of ibase that are greater than  16.
       This  is because numeric constants are recognized syntactically, rather
       than lexically, as described in this volume of POSIX.1‐2008.  They  are
       built  from  lexical  tokens  of single hexadecimal digits and <period>
       characters. Since <blank> characters between tokens are not visible  at
       the  syntactic  level,  it is not possible to recognize the multi-digit
       ``digits'' used in the higher bases properly. The ability to  recognize
       input  in these bases was not considered useful enough to require modi‐
       fying these implementations.  Note that the recognition of numeric con‐
       stants at the syntactic level is not a problem with conformance to this
       volume of POSIX.1‐2008, as it does not impact the behavior of  conform‐
       ing  applications (and correct bc programs). Historical implementations
       also accept input with all of the digits '0'−'9' and 'A'−'F' regardless
       of the value of ibase; since digits with value greater than or equal to
       ibase are not really appropriate, the  behavior	when  they  appear  is
       undefined, except for the common case of:

	       /* Process in octal base. */
	       /* Restore decimal base. */

       In  some historical implementations, if the expression to be written is
       an uninitialized array element, a leading <space>  and/or  up  to  four
       leading	0  characters  may  be	output before the character zero. This
       behavior is considered a bug; it is unlikely that  any  currently  con‐
       forming application relies on:

	   echo 'b[3]' | bc

       returning 00000 rather than 0.

       Exact  calculation  of  the number of fractional digits to output for a
       given value in a base other than 10 can be  computationally  expensive.
       Historical implementations use a faster approximation, and this is per‐
       mitted. Note that the requirements apply only to values of  obase  that
       this  volume  of	 POSIX.1‐2008  requires implementations to support (in
       particular, not to 1, 0, or negative bases, if an  implementation  sup‐
       ports them as an extension).

       Historical  implementations  of bc did not allow array parameters to be
       passed as the last parameter to a  function.  New  implementations  are
       encouraged to remove this restriction even though it is not required by
       the grammar.


       Section 1.3, Grammar Conventions, awk

       The Base Definitions volume of  POSIX.1‐2008,  Chapter  8,  Environment
       Variables, Section 12.2, Utility Syntax Guidelines

       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the	referee document. The original Standard can be obtained online
       at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,	 see  https://www.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013				BC(1P)

List of man pages available for Archlinux

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net