BC(1)

NAME
bc - arbitrary-precision decimal arithmetic language and calculator

SYNOPSIS
bc [-cCghilPqRsvVw] [--digit-clamp] [--no-digit-clamp] [--global-stacks] [--help] [--interactive] [--mathlib] [--no-prompt] [--no-read-prompt] [--quiet] [--standard] [--warn] [--version] [-e expr] [--expression=expr...] [-f file...] [--file=file...] [file...]

DESCRIPTION
bc(1) is an interactive processor for a language first standardized in 1991 by POSIX. (See the STANDARDS section.) The language provides unlimited precision decimal arithmetic and is somewhat C-like, but there are differences. Such differences will be noted in this document.

After parsing and handling options, this bc(1) reads any files given on the command line and executes them before reading from stdin.

This bc(1) is a drop-in replacement for any bc(1), including (and especially) the GNU bc(1). It also has many extensions and extra features beyond other implementations.

Note: If running this bc(1) on any script meant for another bc(1) gives a parse error, it is probably because a word this bc(1) reserves as a keyword is used as the name of a function, variable, or array. To fix that, use the command-line option -r keyword, where keyword is the keyword that is used as a name in the script. For more information, see the OPTIONS section.

If parsing scripts meant for other bc(1) implementations still does not work, that is a bug and should be reported. See the BUGS section.

OPTIONS
The following are the options that bc(1) accepts.

-C, --no-digit-clamp
    Disables clamping of digits greater than or equal to the current ibase when parsing numbers.

    This means that the value added to a number from a digit is always that digit’s value multiplied by the value of ibase raised to the power of the digit’s position, which starts from 0 at the least significant digit.

    If this and/or the -c or --digit-clamp options are given multiple times, the last one given is used.

    This option overrides the BC_DIGIT_CLAMP environment variable (see the ENVIRONMENT VARIABLES section) and the default, which can be queried with the -h or --help options.

    This is a non-portable extension.

-c, --digit-clamp
    Enables clamping of digits greater than or equal to the current ibase when parsing numbers.

    This means that digits that the value added to a number from a digit that is greater than or equal to the ibase is the value of ibase minus 1 all multiplied by the value of ibase raised to the power of the digit’s position, which starts from 0 at the least significant digit.

    If this and/or the -C or --no-digit-clamp options are given multiple times, the last one given is used.

    This option overrides the BC_DIGIT_CLAMP environment variable (see the ENVIRONMENT VARIABLES section) and the default, which can be queried with the -h or --help options.

    This is a non-portable extension.

-e expr, --expression=expr
    Evaluates expr. If multiple expressions are given, they are evaluated in order. If files are given as well (see the -f and --file options), the expressions and files are evaluated in the order given. This means that if a file is given before an expression, the file is read in and evaluated first.

    If this option is given on the command-line (i.e., not in BC_ENV_ARGS, see the ENVIRONMENT VARIABLES section), then after processing all expressions and files, bc(1) will exit, unless - (stdin) was given as an argument at least once to -f or --file, whether on the command-line or in BC_ENV_ARGS. However, if any other -e, --expression, -f, or --file arguments are given after -f- or equivalent is given, bc(1) will give a fatal error and exit.

    This is a non-portable extension.

-f file, --file=file
    Reads in file and evaluates it, line by line, as though it were read through stdin. If expressions are also given (see the -e and --expression options), the expressions are evaluated in the order given.

    If this option is given on the command-line (i.e., not in BC_ENV_ARGS, see the ENVIRONMENT VARIABLES section), then after processing all expressions and files, bc(1) will exit, unless - (stdin) was given as an argument at least once to -f or --file. However, if any other -e, --expression, -f, or --file arguments are given after -f- or equivalent is given, bc(1) will give a fatal error and exit.

    This is a non-portable extension.

-g, --global-stacks
    Turns the globals ibase, obase, and scale into stacks.

    This has the effect that a copy of the current value of all three are pushed onto a stack for every function call, as well as popped when every function returns. This means that functions can assign to any and all of those globals without worrying that the change will affect other functions. Thus, a hypothetical function named output(x,b) that simply printed x in base b could be written like this:

            define void output(x, b) {
                obase=b
                x
            }

    instead of like this:

            define void output(x, b) {
                auto c
                c=obase
                obase=b
                x
                obase=c
            }

    This makes writing functions much easier.

    However, since using this flag means that functions cannot set ibase, obase, or scale globally, functions that are made to do so cannot work anymore. There are two possible use cases for that, and each has a solution.

    First, if a function is called on startup to turn bc(1) into a number converter, it is possible to replace that capability with various shell aliases. Examples:

            alias d2o="bc -e ibase=A -e obase=8"
            alias h2b="bc -e ibase=G -e obase=2"

    Second, if the purpose of a function is to set ibase, obase, or scale globally for any other purpose, it could be split into one to three functions (based on how many globals it sets) and each of those functions could return the desired value for a global.

    If the behavior of this option is desired for every run of bc(1), then users could make sure to define BC_ENV_ARGS and include this option (see the ENVIRONMENT VARIABLES section for more details).

    If -s, -w, or any equivalents are used, this option is ignored.

    This is a non-portable extension.

-h, --help
    Prints a usage message and exits.

-I ibase, --ibase=ibase
    Sets the builtin variable ibase to the value ibase assuming that ibase is in base 10. It is a fatal error if ibase is not a valid number.

    If multiple instances of this option are given, the last is used.

    This is a non-portable extension.

-i, --interactive
    Forces interactive mode. (See the INTERACTIVE MODE section.)

    This is a non-portable extension.

-L, --no-line-length
    Disables line length checking and prints numbers without backslashes and newlines. In other words, this option sets BC_LINE_LENGTH to 0 (see the ENVIRONMENT VARIABLES section).

    This is a non-portable extension.

-l, --mathlib
    Sets scale (see the SYNTAX section) to 20 and loads the included math library before running any code, including any expressions or files specified on the command line.

    To learn what is in the library, see the LIBRARY section.

-O obase, --obase=obase
    Sets the builtin variable obase to the value obase assuming that obase is in base 10. It is a fatal error if obase is not a valid number.

    If multiple instances of this option are given, the last is used.

    This is a non-portable extension.

-P, --no-prompt
    Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode. See the TTY MODE section.) This is mostly for those users that do not want a prompt or are not used to having them in bc(1). Most of those users would want to put this option in BC_ENV_ARGS (see the ENVIRONMENT VARIABLES section).

    These options override the BC_PROMPT and BC_TTY_MODE environment variables (see the ENVIRONMENT VARIABLES section).

    This is a non-portable extension.

-q, --quiet
    This option is for compatibility with the GNU bc(1) (https://www.gnu.org/software/bc/); it is a no-op. Without this option, GNU bc(1) prints a copyright header. This bc(1) only prints the copyright header if one or more of the -v, -V, or --version options are given unless the BC_BANNER environment variable is set and contains a non-zero integer or if this bc(1) was built with the header displayed by default. If any of that is the case, then this option does prevent bc(1) from printing the header.

    This is a non-portable extension.

-R, --no-read-prompt
    Disables the read prompt in TTY mode. (The read prompt is only enabled in TTY mode. See the TTY MODE section.) This is mostly for those users that do not want a read prompt or are not used to having them in bc(1). Most of those users would want to put this option in BC_ENV_ARGS (see the ENVIRONMENT VARIABLES section). This option is also useful in hash bang lines of bc(1) scripts that prompt for user input.

    This option does not disable the regular prompt because the read prompt is only used when the read() built-in function is called.

    These options do override the BC_PROMPT and BC_TTY_MODE environment variables (see the ENVIRONMENT VARIABLES section), but only for the read prompt.

    This is a non-portable extension.

-r keyword, --redefine=keyword
    Redefines keyword in order to allow it to be used as a function, variable, or array name. This is useful when this bc(1) gives parse errors when parsing scripts meant for other bc(1) implementations.

    The keywords this bc(1) allows to be redefined are:

    •   abs

    •   asciify

    •   continue

    •   divmod

    •   else

    •   halt

    •   last

    •   limits

    •   maxibase

    •   maxobase

    •   maxscale

    •   modexp

    •   print

    •   read

    •   stream

    If any of those keywords are used as a function, variable, or array name in a script, use this option with the keyword as the argument. If multiple are used, use this option for all of them; it can be used multiple times.

    Keywords are not redefined when parsing the builtin math library (see the LIBRARY section).

    It is a fatal error to redefine keywords mandated by the POSIX standard (see the STANDARDS section). It is a fatal error to attempt to redefine words that this bc(1) does not reserve as keywords.

-S scale, --scale=scale
    Sets the builtin variable scale to the value scale assuming that scale is in base 10. It is a fatal error if scale is not a valid number.

    If multiple instances of this option are given, the last is used.

    This is a non-portable extension.

-s, --standard
    Process exactly the language defined by the standard (see the STANDARDS section) and error if any extensions are used.

    This is a non-portable extension.

-v, -V, --version
    Print the version information (copyright header) and exits.

    This is a non-portable extension.

-w, --warn
    Like -s and --standard, except that warnings (and not errors) are printed for non-standard extensions and execution continues normally.

    This is a non-portable extension.

-z, --leading-zeroes
    Makes bc(1) print all numbers greater than -1 and less than 1, and not equal to 0, with a leading zero.

    This can be set for individual numbers with the plz(x), plznl(x), pnlz(x), and pnlznl(x) functions in the extended math library (see the LIBRARY section).

    This is a non-portable extension.

All long options are non-portable extensions.

STDIN
If no files or expressions are given by the -f, --file, -e, or --expression options, then bc(1) reads from stdin.

However, there are a few caveats to this.

First, stdin is evaluated a line at a time. The only exception to this is if the parse cannot complete. That means that starting a string without ending it or starting a function, if statement, or loop without ending it will also cause bc(1) to not execute.

Second, after an if statement, bc(1) doesn’t know if an else statement will follow, so it will not execute until it knows there will not be an else statement.

STDOUT
Any non-error output is written to stdout. In addition, if history (see the HISTORY section) and the prompt (see the TTY MODE section) are enabled, both are output to stdout.

Note: Unlike other bc(1) implementations, this bc(1) will issue a fatal error (see the EXIT STATUS section) if it cannot write to stdout, so if stdout is closed, as in bc >&-, it will quit with an error. This is done so that bc(1) can report problems when stdout is redirected to a file.

If there are scripts that depend on the behavior of other bc(1) implementations, it is recommended that those scripts be changed to redirect stdout to /dev/null.

STDERR
Any error output is written to stderr.

Note: Unlike other bc(1) implementations, this bc(1) will issue a fatal error (see the EXIT STATUS section) if it cannot write to stderr, so if stderr is closed, as in bc 2>&-, it will quit with an error. This is done so that bc(1) can exit with an error code when stderr is redirected to a file.

If there are scripts that depend on the behavior of other bc(1) implementations, it is recommended that those scripts be changed to redirect stderr to /dev/null.

SYNTAX
The syntax for bc(1) programs is mostly C-like, with some differences. This bc(1) follows the POSIX standard (see the STANDARDS section), which is a much more thorough resource for the language this bc(1) accepts. This section is meant to be a summary and a listing of all the extensions to the standard.

In the sections below, E means expression, S means statement, and I means identifier.

Identifiers (I) start with a lowercase letter and can be followed by any number (up to BC_NAME_MAX-1) of lowercase letters (a-z), digits (0-9), and underscores (_). The regex is [a-z][a-z0-9_]*. Identifiers with more than one character (letter) are a non-portable extension.

ibase is a global variable determining how to interpret constant numbers. It is the “input” base, or the number base used for interpreting input numbers. ibase is initially 10. If the -s (--standard) and -w (--warn) flags were not given on the command line, the max allowable value for ibase is 36. Otherwise, it is 16. The min allowable value for ibase is 2. The max allowable value for ibase can be queried in bc(1) programs with the maxibase() built-in function.

obase is a global variable determining how to output results. It is the “output” base, or the number base used for outputting numbers. obase is initially 10. The max allowable value for obase is BC_BASE_MAX and can be queried in bc(1) programs with the maxobase() built-in function. The min allowable value for obase is 2. Values are output in the specified base.

The scale of an expression is the number of digits in the result of the expression right of the decimal point, and scale is a global variable that sets the precision of any operations, with exceptions. scale is initially 0. scale cannot be negative. The max allowable value for scale is BC_SCALE_MAX and can be queried in bc(1) programs with the maxscale() built-in function.

bc(1) has both global variables and local variables. All local variables are local to the function; they are parameters or are introduced in the auto list of a function (see the FUNCTIONS section). If a variable is accessed which is not a parameter or in the auto list, it is assumed to be global. If a parent function has a local variable version of a variable that a child function considers global, the value of that global variable in the child function is the value of the variable in the parent function, not the value of the actual global variable.

All of the above applies to arrays as well.

The value of a statement that is an expression (i.e., any of the named expressions or operands) is printed unless the lowest precedence operator is an assignment operator and the expression is notsurrounded by parentheses.

The value that is printed is also assigned to the special variable last. A single dot (.) may also be used as a synonym for last. These are non-portable extensions.

Either semicolons or newlines may separate statements.

  Comments
There are two kinds of comments:

1.  Block comments are enclosed in /* and */.

2.  Line comments go from # until, and not including, the next newline. This is a non-portable extension.

  Named Expressions
The following are named expressions in bc(1):

1.  Variables: I

2.  Array Elements: I[E]

3.  ibase

4.  obase

5.  scale

6.  last or a single dot (.)

Number 6 is a non-portable extension.

Variables and arrays do not interfere; users can have arrays named the same as variables. This also applies to functions (see the FUNCTIONS section), so a user can have a variable, array, and function that all have the same name, and they will not shadow each other, whether inside of functions or not.

Named expressions are required as the operand of increment/decrement operators and as the left side of assignment operators (see the Operators subsection).

  Operands
The following are valid operands in bc(1):

1.  Numbers (see the Numbers subsection below).

2.  Array indices (I[E]).

3.  (E): The value of E (used to change precedence).

4.  sqrt(E): The square root of E. E must be non-negative.

5.  length(E): The number of significant decimal digits in E. Returns 1 for 0 with no decimal places. If given a string, the length of the string is returned. Passing a string to length(E) is a non-portable extension.

6.  length(I[]): The number of elements in the array I. This is a non-portable extension.

7.  scale(E): The scale of E.

8.  abs(E): The absolute value of E. This is a non-portable extension.

9.  is_number(E): 1 if the given argument is a number, 0 if it is a string. This is a non-portable extension.

10. is_string(E): 1 if the given argument is a string, 0 if it is a number. This is a non-portable extension.

11. modexp(E, E, E): Modular exponentiation, where the first expression is the base, the second is the exponent, and the third is the modulus. All three values must be integers. The second argument must be non-negative. The third argument must be non-zero. This is a non-portable extension.

12. divmod(E, E, I[]): Division and modulus in one operation. This is for optimization. The first expression is the dividend, and the second is the divisor, which must be non-zero. The return value is the quotient, and the modulus is stored in index 0 of the provided array (the last argument). This is a non-portable extension.

13. asciify(E): If E is a string, returns a string that is the first letter of its argument. If it is a number, calculates the number mod 256 and returns that number as a one-character string. This is a non-portable extension.

14. asciify(I[]): A string that is made up of the characters that would result from running asciify(E) on each element of the array identified by the argument. This allows creating multi-character strings and storing them. This is a non-portable extension.

15. I(), I(E), I(E, E), and so on, where I is an identifier for a non-void function (see the Void Functions subsection of the FUNCTIONS section). The E argument(s) may also be arrays of the form I[], which will automatically be turned into array references (see the Array References subsection of the FUNCTIONS section) if the corresponding parameter in the function definition is an array reference.

16. read(): Reads a line from stdin and uses that as an expression. The result of that expression is the result of the read() operand. This is a non-portable extension.

17. maxibase(): The max allowable ibase. This is a non-portable extension.

18. maxobase(): The max allowable obase. This is a non-portable extension.

19. maxscale(): The max allowable scale. This is a non-portable extension.

20. line_length(): The line length set with BC_LINE_LENGTH (see the ENVIRONMENT VARIABLES section). This is a non-portable extension.

21. global_stacks(): 0 if global stacks are not enabled with the -g or --global-stacks options, non-zero otherwise. See the OPTIONS section. This is a non-portable extension.

22. leading_zero(): 0 if leading zeroes are not enabled with the -z or –leading-zeroes options, non-zero otherwise. See the OPTIONS section. This is a non-portable extension.

  Numbers
Numbers are strings made up of digits, uppercase letters, and at most 1 period for a radix. Numbers can have up to BC_NUM_MAX digits. Uppercase letters are equal to 9 plus their position in the alphabet, starting from 1 (i.e., A equals 10, or 9+1).

If a digit or letter makes no sense with the current value of ibase (i.e., they are greater than or equal to the current value of ibase), then the behavior depends on the existence of the -c/--digit-clamp or -C/--no-digit-clamp options (see the OPTIONS section), the existence and setting of the BC_DIGIT_CLAMP environment variable (see the ENVIRONMENT VARIABLES section), or the default, which can be queried with the -h/--help option.

If clamping is off, then digits or letters that are greater than or equal to the current value of ibase are not changed. Instead, their given value is multiplied by the appropriate power of ibase and added into the number. This means that, with an ibase of 3, the number AB is equal to 3^1*A+3^0*B, which is 3 times 10 plus 11, or 41.

If clamping is on, then digits or letters that are greater than or equal to the current value of ibase are set to the value of the highest valid digit in ibase before being multiplied by the appropriate power of ibase and added into the number. This means that, with an ibase of 3, the number AB is equal to 3^1*2+3^0*2, which is 3 times 2 plus 2, or 8.

There is one exception to clamping: single-character numbers (i.e., A alone). Such numbers are never clamped and always take the value they would have in the highest possible ibase. This means that A alone always equals decimal 10 and Z alone always equals decimal 35. This behavior is mandated by the standard (see the STANDARDS section) and is meant to provide an easy way to set the current ibase (with the i command) regardless of the current value of ibase.

If clamping is on, and the clamped value of a character is needed, use a leading zero, i.e., for A, use 0A.

  Operators
The following arithmetic and logical operators can be used. They are listed in order of decreasing precedence. Operators in the same group have the same precedence.

++ --
    Type: Prefix and Postfix

    Associativity: None

    Description: increment, decrement

- ! Type: Prefix

    Associativity: None

    Description: negation, boolean not

^   Type: Binary

    Associativity: Right

    Description: power

* / %
    Type: Binary

    Associativity: Left

    Description: multiply, divide, modulus

+ - Type: Binary

    Associativity: Left

    Description: add, subtract

= += -= *= /= %= ^=
    Type: Binary

    Associativity: Right

    Description: assignment

== <= >= != < >
    Type: Binary

    Associativity: Left

    Description: relational

&&  Type: Binary

    Associativity: Left

    Description: boolean and

||  Type: Binary

    Associativity: Left

    Description: boolean or

The operators will be described in more detail below.

++ --
    The prefix and postfix increment and decrement operators behave exactly like they would in C. They require a named expression (see the Named Expressions subsection) as an operand.

    The prefix versions of these operators are more efficient; use them where possible.

-   The negation operator returns 0 if a user attempts to negate any expression with the value 0. Otherwise, a copy of the expression with its sign flipped is returned.

!   The boolean not operator returns 1 if the expression is 0, or 0 otherwise.

    Warning: This operator has a different precedence than the equivalent operator in GNU bc(1) and other bc(1) implementations!

    This is a non-portable extension.

^   The power operator (not the exclusive or operator, as it would be in C) takes two expressions and raises the first to the power of the value of the second. The scale of the result is equal to scale.

    The second expression must be an integer (no scale), and if it is negative, the first value must be non-zero.

*   The multiply operator takes two expressions, multiplies them, and returns the product. If a is the scale of the first expression and b is the scale of the second expression, the scale of the result is equal to min(a+b,max(scale,a,b)) where min() and max() return the obvious values.

/   The divide operator takes two expressions, divides them, and returns the quotient. The scale of the result shall be the value of scale.

    The second expression must be non-zero.

%   The modulus operator takes two expressions, a and b, and evaluates them by 1) Computing a/b to current scale and 2) Using the result of step 1 to calculate a-(a/b)*b to scale max(scale+scale(b),scale(a)).

    The second expression must be non-zero.

+   The add operator takes two expressions, a and b, and returns the sum, with a scale equal to the max of the scales of a and b.

-   The subtract operator takes two expressions, a and b, and returns the difference, with a scale equal to the max of the scales of a and b.

= += -= *= /= %= ^=
    The assignment operators take two expressions, a and b where a is a named expression (see the Named Expressions subsection).

    For =, b is copied and the result is assigned to a. For all others, a and b are applied as operands to the corresponding arithmetic operator and the result is assigned to a.

== <= >= != < >
    The relational operators compare two expressions, a and b, and if the relation holds, according to C language semantics, the result is 1. Otherwise, it is 0.

    Note that unlike in C, these operators have a lower precedence than the assignment operators, which means that a=b>c is interpreted as (a=b)>c.

    Also, unlike the standard (see the STANDARDS section) requires, these operators can appear anywhere any other expressions can be used. This allowance is a non-portable extension.

&&  The boolean and operator takes two expressions and returns 1 if both expressions are non-zero, 0 otherwise.

    This is not a short-circuit operator.

    This is a non-portable extension.

||  The boolean or operator takes two expressions and returns 1 if one of the expressions is non-zero, 0 otherwise.

    This is not a short-circuit operator.

    This is a non-portable extension.

  Statements
The following items are statements:

1.  E

2.  { S ; ... ; S }

3.  if ( E ) S

4.  if ( E ) S else S

5.  while ( E ) S

6.  for ( E ; E ; E ) S

7.  An empty statement

8.  break

9.  continue

10. quit

11. halt

12. limits

13. A string of characters, enclosed in double quotes

14. print E , ... , E

15. stream E , ... , E

16. I(), I(E), I(E, E), and so on, where I is an identifier for a void function (see the Void Functions subsection of the FUNCTIONS section). The E argument(s) may also be arrays of the form I[], which will automatically be turned into array references (see the Array References subsection of the FUNCTIONS section) if the corresponding parameter in the function definition is an array reference.

Numbers 4, 9, 11, 12, 14, 15, and 16 are non-portable extensions.

Also, as a non-portable extension, any or all of the expressions in the header of a for loop may be omitted. If the condition (second expression) is omitted, it is assumed to be a constant 1.

The break statement causes a loop to stop iterating and resume execution immediately following a loop. This is only allowed in loops.

The continue statement causes a loop iteration to stop early and returns to the start of the loop, including testing the loop condition. This is only allowed in loops.

The if else statement does the same thing as in C.

The quit statement causes bc(1) to quit, even if it is on a branch that will not be executed (it is a compile-time command).

Warning: The behavior of this bc(1) on quit is slightly different from other bc(1) implementations. Other bc(1) implementations will exit as soon as they finish parsing the line that a quit command is on. This bc(1) will execute any completed and executable statements that occur before the quit statement before exiting.

In other words, for the bc(1) code below:

        for (i = 0; i < 3; ++i) i; quit

Other bc(1) implementations will print nothing, and this bc(1) will print 0, 1, and 2 on successive lines before exiting.

The halt statement causes bc(1) to quit, if it is executed. (Unlike quit if it is on a branch of an if statement that is not executed, bc(1) does not quit.)

The limits statement prints the limits that this bc(1) is subject to. This is like the quit statement in that it is a compile-time command.

An expression by itself is evaluated and printed, followed by a newline.

  Strings
If strings appear as a statement by themselves, they are printed without a trailing newline.

In addition to appearing as a lone statement by themselves, strings can be assigned to variables and array elements. They can also be passed to functions in variable parameters.

If any statement that expects a string is given a variable that had a string assigned to it, the statement acts as though it had received a string.

If any math operation is attempted on a string or a variable or array element that has been assigned a string, an error is raised, and bc(1) resets (see the RESET section).

Assigning strings to variables and array elements and passing them to functions are non-portable extensions.

  Print Statement
The “expressions” in a print statement may also be strings. If they are, there are backslash escape sequences that are interpreted specially. What those sequences are, and what they cause to be printed, are shown below:

\a: \a

\b: \b

\\: \

\e: \

\f: \f

\n: \n

\q: “

\r: \r

\t: \t

Any other character following a backslash causes the backslash and character to be printed as-is.

Any non-string expression in a print statement shall be assigned to last, like any other expression that is printed.

  Stream Statement
The expressions in a stream statement may also be strings.

If a stream statement is given a string, it prints the string as though the string had appeared as its own statement. In other words, the stream statement prints strings normally, without a newline.

If a stream statement is given a number, a copy of it is truncated and its absolute value is calculated. The result is then printed as though obase is 256 and each digit is interpreted as an 8-bit ASCII character, making it a byte stream.

  Order of Evaluation
All expressions in a statment are evaluated left to right, except as necessary to maintain order of operations. This means, for example, assuming that i is equal to 0, in the expression

        a[i++] = i++

the first (or 0th) element of a is set to 1, and i is equal to 2 at the end of the expression.

This includes function arguments. Thus, assuming i is equal to 0, this means that in the expression

        x(i++, i++)

the first argument passed to x() is 0, and the second argument is 1, while i is equal to 2 before the function starts executing.

FUNCTIONS
Function definitions are as follows:

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

Any I in the parameter list or auto list may be replaced with I[] to make a parameter or auto var an array, and any I in the parameter list may be replaced with *I[] to make a parameter an array reference. Callers of functions that take array references should not put an asterisk in the call; they must be called with just I[] like normal array parameters and will be automatically converted into references.

As a non-portable extension, the opening brace of a define statement may appear on the next line.

As a non-portable extension, the return statement may also be in one of the following forms:

1.  return

2.  return ( )

3.  return E

The first two, or not specifying a return statement, is equivalent to return (0), unless the function is a void function (see the Void Functions subsection below).

  Void Functions
Functions can also be void functions, defined as follows:

        define void I(I,...,I){
            auto I,...,I
            S;...;S
            return
        }

They can only be used as standalone expressions, where such an expression would be printed alone, except in a print statement.

Void functions can only use the first two return statements listed above. They can also omit the return statement entirely.

The word “void” is not treated as a keyword; it is still possible to have variables, arrays, and functions named void. The word “void” is only treated specially right after the define keyword.

This is a non-portable extension.

  Array References
For any array in the parameter list, if the array is declared in the form

        *I[]

it is a reference. Any changes to the array in the function are reflected, when the function returns, to the array that was passed in.

Other than this, all function arguments are passed by value.

This is a non-portable extension.

LIBRARY
All of the functions below are available when the -l or --mathlib command-line flags are given.

  Standard Library
The standard (see the STANDARDS section) defines the following functions for the math library:

s(x)
    Returns the sine of x, which is assumed to be in radians.

    This is a transcendental function (see the Transcendental Functions subsection below).

c(x)
    Returns the cosine of x, which is assumed to be in radians.

    This is a transcendental function (see the Transcendental Functions subsection below).

a(x)
    Returns the arctangent of x, in radians.

    This is a transcendental function (see the Transcendental Functions subsection below).

l(x)
    Returns the natural logarithm of x.

    This is a transcendental function (see the Transcendental Functions subsection below).

e(x)
    Returns the mathematical constant e raised to the power of x.

    This is a transcendental function (see the Transcendental Functions subsection below).

j(x, n)
    Returns the bessel integer order n (truncated) of x.

    This is a transcendental function (see the Transcendental Functions subsection below).

  Transcendental Functions
All transcendental functions can return slightly inaccurate results, up to 1 ULP (https://en.wikipedia.org/wiki/Unit_in_the_last_place). This is unavoidable, and the article at https://people.eecs.berkeley.edu/~wkahan/LOG10HAF.TXT explains why it is impossible and unnecessary to calculate exact results for the transcendental functions.

Because of the possible inaccuracy, I recommend that users call those functions with the precision (scale) set to at least 1 higher than is necessary. If exact results are absolutely required, users can double the precision (scale) and then truncate.

The transcendental functions in the standard math library are:

•   s(x)

•   c(x)

•   a(x)

•   l(x)

•   e(x)

•   j(x, n)

RESET
When bc(1) encounters an error or a signal that it has a non-default handler for, it resets. This means that several things happen.

First, any functions that are executing are stopped and popped off the stack. The behavior is not unlike that of exceptions in programming languages. Then the execution point is set so that any code waiting to execute (after all functions returned) is skipped.

Thus, when bc(1) resets, it skips any remaining code waiting to be executed. Then, if it is interactive mode, and the error was not a fatal error (see the EXIT STATUS section), it asks for more input; otherwise, it exits with the appropriate return code.

Note that this reset behavior is different from the GNU bc(1), which attempts to start executing the statement right after the one that caused an error.

PERFORMANCE
Most bc(1) implementations use char types to calculate the value of 1 decimal digit at a time, but that can be slow. This bc(1) does something different.

It uses large integers to calculate more than 1 decimal digit at a time. If built in a environment where BC_LONG_BIT (see the LIMITS section) is 64, then each integer has 9 decimal digits. If built in an environment where BC_LONG_BIT is 32 then each integer has 4 decimal digits. This value (the number of decimal digits per large integer) is called BC_BASE_DIGS.

The actual values of BC_LONG_BIT and BC_BASE_DIGS can be queried with the limits statement.

In addition, this bc(1) uses an even larger integer for overflow checking. This integer type depends on the value of BC_LONG_BIT, but is always at least twice as large as the integer type used to store digits.

LIMITS
The following are the limits on bc(1):

BC_LONG_BIT
    The number of bits in the long type in the environment where bc(1) was built. This determines how many decimal digits can be stored in a single large integer (see the PERFORMANCE section).

BC_BASE_DIGS
    The number of decimal digits per large integer (see the PERFORMANCE section). Depends on BC_LONG_BIT.

BC_BASE_POW
    The max decimal number that each large integer can store (see BC_BASE_DIGS) plus 1. Depends on BC_BASE_DIGS.

BC_OVERFLOW_MAX
    The max number that the overflow type (see the PERFORMANCE section) can hold. Depends on BC_LONG_BIT.

BC_BASE_MAX
    The maximum output base. Set at BC_BASE_POW.

BC_DIM_MAX
    The maximum size of arrays. Set at SIZE_MAX-1.

BC_SCALE_MAX
    The maximum scale. Set at BC_OVERFLOW_MAX-1.

BC_STRING_MAX
    The maximum length of strings. Set at BC_OVERFLOW_MAX-1.

BC_NAME_MAX
    The maximum length of identifiers. Set at BC_OVERFLOW_MAX-1.

BC_NUM_MAX
    The maximum length of a number (in decimal digits), which includes digits after the decimal point. Set at BC_OVERFLOW_MAX-1.

Exponent
    The maximum allowable exponent (positive or negative). Set at BC_OVERFLOW_MAX.

Number of vars
    The maximum number of vars/arrays. Set at SIZE_MAX-1.

The actual values can be queried with the limits statement.

These limits are meant to be effectively non-existent; the limits are so large (at least on 64-bit machines) that there should not be any point at which they become a problem. In fact, memory should be exhausted before these limits should be hit.

ENVIRONMENT VARIABLES
As non-portable extensions, bc(1) recognizes the following environment variables:

POSIXLY_CORRECT
    If this variable exists (no matter the contents), bc(1) behaves as if the -s option was given.

BC_ENV_ARGS
    This is another way to give command-line arguments to bc(1). They should be in the same format as all other command-line arguments. These are always processed first, so any files given in BC_ENV_ARGS will be processed before arguments and files given on the command-line. This gives the user the ability to set up “standard” options and files to be used at every invocation. The most useful thing for such files to contain would be useful functions that the user might want every time bc(1) runs.

    The code that parses BC_ENV_ARGS will correctly handle quoted arguments, but it does not understand escape sequences. For example, the string “/home/gavin/some bc file.bc” will be correctly parsed, but the string “/home/gavin/some "bc" file.bc” will include the backslashes.

    The quote parsing will handle either kind of quotes, ’ or “. Thus, if you have a file with any number of single quotes in the name, you can use double quotes as the outside quotes, as in “some `bc' file.bc”, and vice versa if you have a file with double quotes. However, handling a file with both kinds of quotes in BC_ENV_ARGS is not supported due to the complexity of the parsing, though such files are still supported on the command-line where the parsing is done by the shell.

BC_LINE_LENGTH
    If this environment variable exists and contains an integer that is greater than 1 and is less than UINT16_MAX (2^16-1), bc(1) will output lines to that length, including the backslash (\). The default line length is 70.

    The special value of 0 will disable line length checking and print numbers without regard to line length and without backslashes and newlines.

BC_BANNER
    If this environment variable exists and contains an integer, then a non-zero value activates the copyright banner when bc(1) is in interactive mode, while zero deactivates it.

    If bc(1) is not in interactive mode (see the INTERACTIVE MODE section), then this environment variable has no effect because bc(1) does not print the banner when not in interactive mode.

    This environment variable overrides the default, which can be queried with the -h or --help options.

BC_SIGINT_RESET
    If bc(1) is not in interactive mode (see the INTERACTIVE MODE section), then this environment variable has no effect because bc(1) exits on SIGINT when not in interactive mode.

    However, when bc(1) is in interactive mode, then if this environment variable exists and contains an integer, a non-zero value makes bc(1) reset on SIGINT, rather than exit, and zero makes bc(1) exit. If this environment variable exists and is not an integer, then bc(1) will exit on SIGINT.

    This environment variable overrides the default, which can be queried with the -h or --help options.

BC_TTY_MODE
    If TTY mode is not available (see the TTY MODE section), then this environment variable has no effect.

    However, when TTY mode is available, then if this environment variable exists and contains an integer, then a non-zero value makes bc(1) use TTY mode, and zero makes bc(1) not use TTY mode.

    This environment variable overrides the default, which can be queried with the -h or --help options.

BC_PROMPT
    If TTY mode is not available (see the TTY MODE section), then this environment variable has no effect.

    However, when TTY mode is available, then if this environment variable exists and contains an integer, a non-zero value makes bc(1) use a prompt, and zero or a non-integer makes bc(1) not use a prompt. If this environment variable does not exist and BC_TTY_MODE does, then the value of the BC_TTY_MODE environment variable is used.

    This environment variable and the BC_TTY_MODE environment variable override the default, which can be queried with the -h or --help options.

BC_EXPR_EXIT
    If any expressions or expression files are given on the command-line with -e, --expression, -f, or --file, then if this environment variable exists and contains an integer, a non-zero value makes bc(1) exit after executing the expressions and expression files, and a zero value makes bc(1) not exit.

    This environment variable overrides the default, which can be queried with the -h or --help options.

BC_DIGIT_CLAMP
    When parsing numbers and if this environment variable exists and contains an integer, a non-zero value makes bc(1) clamp digits that are greater than or equal to the current ibase so that all such digits are considered equal to the ibase minus 1, and a zero value disables such clamping so that those digits are always equal to their value, which is multiplied by the power of the ibase.

    This never applies to single-digit numbers, as per the standard (see the STANDARDS section).

    This environment variable overrides the default, which can be queried with the -h or --help options.

EXIT STATUS
bc(1) returns the following exit statuses:

0   No error.

1   A math error occurred. This follows standard practice of using 1 for expected errors, since math errors will happen in the process of normal execution.

    Math errors include divide by 0, taking the square root of a negative number, attempting to convert a negative number to a hardware integer, overflow when converting a number to a hardware integer, overflow when calculating the size of a number, and attempting to use a non-integer where an integer is required.

    Converting to a hardware integer happens for the second operand of the power (^) operator and the corresponding assignment operator.

2   A parse error occurred.

    Parse errors include unexpected EOF, using an invalid character, failing to find the end of a string or comment, using a token where it is invalid, giving an invalid expression, giving an invalid print statement, giving an invalid function definition, attempting to assign to an expression that is not a named expression (see the Named Expressions subsection of the SYNTAX section), giving an invalid auto list, having a duplicate auto/function parameter, failing to find the end of a code block, attempting to return a value from a void function, attempting to use a variable as a reference, and using any extensions when the option -s or any equivalents were given.

3   A runtime error occurred.

    Runtime errors include assigning an invalid number to any global (ibase, obase, or scale), giving a bad expression to a read() call, calling read() inside of a read() call, type errors, passing the wrong number of arguments to functions, attempting to call an undefined function, and attempting to use a void function call as a value in an expression.

4   A fatal error occurred.

    Fatal errors include memory allocation errors, I/O errors, failing to open files, attempting to use files that do not have only ASCII characters (bc(1) only accepts ASCII characters), attempting to open a directory as a file, and giving invalid command-line options.

The exit status 4 is special; when a fatal error occurs, bc(1) always exits and returns 4, no matter what mode bc(1) is in.

The other statuses will only be returned when bc(1) is not in interactive mode (see the INTERACTIVE MODE section), since bc(1) resets its state (see the RESET section) and accepts more input when one of those errors occurs in interactive mode. This is also the case when interactive mode is forced by the -i flag or --interactive option.

These exit statuses allow bc(1) to be used in shell scripting with error checking, and its normal behavior can be forced by using the -i flag or --interactive option.

INTERACTIVE MODE
Per the standard (see the STANDARDS section), bc(1) has an interactive mode and a non-interactive mode. Interactive mode is turned on automatically when both stdin and stdout are hooked to a terminal, but the -i flag and --interactive option can turn it on in other situations.

In interactive mode, bc(1) attempts to recover from errors (see the RESET section), and in normal execution, flushes stdout as soon as execution is done for the current input. bc(1) may also reset on SIGINT instead of exit, depending on the contents of, or default for, the BC_SIGINT_RESET environment variable (see the ENVIRONMENT VARIABLES section).

TTY MODE
If stdin, stdout, and stderr are all connected to a TTY, then “TTY mode” is considered to be available, and thus, bc(1) can turn on TTY mode, subject to some settings.

If there is the environment variable BC_TTY_MODE in the environment (see the ENVIRONMENT VARIABLES section), then if that environment variable contains a non-zero integer, bc(1) will turn on TTY mode when stdin, stdout, and stderr are all connected to a TTY. If the BC_TTY_MODE environment variable exists but is not a non-zero integer, then bc(1) will not turn TTY mode on.

If the environment variable BC_TTY_MODE does not exist, the default setting is used. The default setting can be queried with the -h or --help options.

TTY mode is different from interactive mode because interactive mode is required in the bc(1) standard (see the STANDARDS section), and interactive mode requires only stdin and stdout to be connected to a terminal.

  Command-Line History
Command-line history is only enabled if TTY mode is, i.e., that stdin, stdout, and stderr are connected to a TTY and the BC_TTY_MODE environment variable (see the ENVIRONMENT VARIABLES section) and its default do not disable TTY mode. See the COMMAND LINE HISTORY section for more information.

  Prompt
If TTY mode is available, then a prompt can be enabled. Like TTY mode itself, it can be turned on or off with an environment variable: BC_PROMPT (see the ENVIRONMENT VARIABLES section).

If the environment variable BC_PROMPT exists and is a non-zero integer, then the prompt is turned on when stdin, stdout, and stderr are connected to a TTY and the -P and --no-prompt options were not used. The read prompt will be turned on under the same conditions, except that the -R and --no-read-prompt options must also not be used.

However, if BC_PROMPT does not exist, the prompt can be enabled or disabled with the BC_TTY_MODE environment variable, the -P and --no-prompt options, and the -R and --no-read-prompt options. See the ENVIRONMENT VARIABLES and OPTIONS sections for more details.

SIGNAL HANDLING
Sending a SIGINT will cause bc(1) to do one of two things.

If bc(1) is not in interactive mode (see the INTERACTIVE MODE section), or the BC_SIGINT_RESET environment variable (see the ENVIRONMENT VARIABLES section), or its default, is either not an integer or it is zero, bc(1) will exit.

However, if bc(1) is in interactive mode, and the BC_SIGINT_RESET or its default is an integer and non-zero, then bc(1) will stop executing the current input and reset (see the RESET section) upon receiving a SIGINT.

Note that “current input” can mean one of two things. If bc(1) is processing input from stdin in interactive mode, it will ask for more input. If bc(1) is processing input from a file in interactive mode, it will stop processing the file and start processing the next file, if one exists, or ask for input from stdin if no other file exists.

This means that if a SIGINT is sent to bc(1) as it is executing a file, it can seem as though bc(1) did not respond to the signal since it will immediately start executing the next file. This is by design; most files that users execute when interacting with bc(1) have function definitions, which are quick to parse. If a file takes a long time to execute, there may be a bug in that file. The rest of the files could still be executed without problem, allowing the user to continue.

SIGTERM and SIGQUIT cause bc(1) to clean up and exit, and it uses the default handler for all other signals. The one exception is SIGHUP; in that case, and only when bc(1) is in TTY mode (see the TTY MODE section), a SIGHUP will cause bc(1) to clean up and exit.

COMMAND LINE HISTORY
bc(1) supports interactive command-line editing.

If bc(1) can be in TTY mode (see the TTY MODE section), history can be enabled. This means that command-line history can only be enabled when stdin, stdout, and stderr are all connected to a TTY.

Like TTY mode itself, it can be turned on or off with the environment variable BC_TTY_MODE (see the ENVIRONMENT VARIABLES section).

If history is enabled, previous lines can be recalled and edited with the arrow keys.

Note: tabs are converted to 8 spaces.

LOCALES
This bc(1) ships with support for adding error messages for different locales and thus, supports LC_MESSAGES.

SEE ALSO
dc(1)

STANDARDS
bc(1) is compliant with the IEEE Std 1003.1-2017 (“POSIX.1-2017”) specification at https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html . The flags -efghiqsvVw, all long options, and the extensions noted above are extensions to that specification.

In addition, the behavior of the quit implements an interpretation of that specification that is different from all known implementations. For more information see the Statements subsection of the SYNTAX section.

Note that the specification explicitly says that bc(1) only accepts numbers that use a period (.) as a radix point, regardless of the value of LC_NUMERIC.

This bc(1) supports error messages for different locales, and thus, it supports LC_MESSAGES.

BUGS
Before version 6.1.0, this bc(1) had incorrect behavior for the quit statement.

No other bugs are known. Report bugs at https://git.gavinhoward.com/gavin/bc .

AUTHORS
Gavin D. Howard gavin@gavinhoward.com and contributors.