BC(1)

NAME

bc - arbitrary-precision arithmetic language and calculator

SYNOPSIS

bc [-ghilPqsvVw] [--global-stacks] [--help] [--interactive] [--mathlib] [--no-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 (https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html).) 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).

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).

    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.

    This is a non-portable extension.

-s, --standard
    Process exactly the language defined by the standard (https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html) 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.

    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 that, 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.

    After processing all expressions and files, bc(1) will exit, unless - (stdin) was given as an argument at least once to -f or --file.

    This is a non-portable extension.

All long options are non-portable extensions.

STDOUT

Any non-error output is written 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 (https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html), 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.

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.  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.

10. 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.

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

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

13. 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 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 (https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html) 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. 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, and 15 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.

  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.

  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 (https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html) 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 this article (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

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.

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, 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 ibase, obase, or scale; give 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 (https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html), 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 cases.

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.

TTY MODE

If stdin, stdout, and stderr are all connected to a TTY, bc(1) turns on "TTY mode."

TTY mode is required for history to be enabled (see the COMMAND LINE HISTORY section). It is also required to enable special handling for SIGINT signals.

The prompt is enabled in TTY mode.

TTY mode is different from interactive mode because interactive mode is required in the bc(1) specification (https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html), and interactive mode requires only stdin and stdout to be connected to a terminal.

SIGNAL HANDLING

Sending a SIGINT will cause bc(1) to stop execution of the current input. If bc(1) is in TTY mode (see the TTY MODE section), it will reset (see the RESET section). Otherwise, it will clean up and exit.

Note that "current input" can mean one of two things. If bc(1) is processing input from stdin in TTY mode, it will ask for more input. If bc(1) is processing input from a file in TTY 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, when bc(1) is in TTY mode, a SIGHUP will cause bc(1) to clean up and exit.

COMMAND LINE HISTORY

bc(1) supports interactive command-line editing. If bc(1) is in TTY mode (see the TTY MODE section), 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”) (https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html) 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.

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

BUGS

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

AUTHORS

Gavin D. Howard <yzena.tech@gmail.com> and contributors.