<!---

SPDX-License-Identifier: BSD-2-Clause

Copyright (c) 2018-2021 Gavin D. Howard and contributors.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

-->

# NAME

bc - arbitrary-precision decimal arithmetic language and calculator

# SYNOPSIS

**bc** [**-ghilPqRsvVw**] [**-\-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. (The current standard is [here][1].) 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).

**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.

**-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 quits.

**-i**, **-\-interactive**

:   Forces interactive mode. (See the **INTERACTIVE MODE** 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.

**-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**.

**-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. It
    is a fatal error to attempt to redefine words that this bc(1) does not
    reserve as keywords.

**-q**, **-\-quiet**

:   This option is for compatibility with the [GNU bc(1)][2]; 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.

    This is a **non-portable extension**.

**-s**, **-\-standard**

:   Process exactly the language defined by the [standard][1] and error if any
    extensions are used.

    This is a **non-portable extension**.

**-v**, **-V**, **-\-version**

:   Print the version information (copyright header) and exit.

    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**.

**-e** *expr*, **-\-expression**=*expr*

:   Evaluates *expr*. If multiple expressions are given, they are evaluated in
    order. If files are given as well (see below), 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 above), 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**.

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) read 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 <file> >&-**, 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 <file> 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][1], 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.	**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**.
10.	**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**.
11.	**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**.
12.	**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.
13.	**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**.
14.	**maxibase()**: The max allowable **ibase**. This is a **non-portable
	extension**.
15.	**maxobase()**: The max allowable **obase**. This is a **non-portable
	extension**.
16.	**maxscale()**: The max allowable **scale**. 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** + their position in the alphabet (i.e., **A** equals
**10**, or **9+1**). If a digit or letter makes no sense with the current value
of **ibase**, they are set to the value of the highest valid digit in **ibase**.

Single-character numbers (i.e., **A** alone) take the value that they would have
if they were valid digits, regardless of the value of **ibase**. This means that
**A** alone always equals decimal **10** and **Z** alone always equals decimal
**35**.

## 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.

    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 *scale*s 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 *scale*s 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][1] 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).

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][1] 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][4]). This is unavoidable, and [this article][5] 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

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**.

**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.

# 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][1], 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) specification][1], 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.

# SEE ALSO

dc(1)

# STANDARDS

bc(1) is compliant with the [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1]
specification. The flags **-efghiqsvVw**, all long options, and the extensions
noted above are extensions to that specification.

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**.

# BUGS

None are known. Report bugs at https://git.yzena.com/gavin/bc.

# AUTHORS

Gavin D. Howard <gavin@yzena.com> and contributors.

[1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html
[2]: https://www.gnu.org/software/bc/
[3]: https://en.wikipedia.org/wiki/Rounding#Round_half_away_from_zero
[4]: https://en.wikipedia.org/wiki/Unit_in_the_last_place
[5]: https://people.eecs.berkeley.edu/~wkahan/LOG10HAF.TXT
[6]: https://en.wikipedia.org/wiki/Rounding#Rounding_away_from_zero
