freebsd-dev/contrib/bc/manuals/dc/EHN.1.md

Name

dc - arbitrary-precision decimal reverse-Polish notation calculator

SYNOPSIS

dc [-hiPRvVx] [--version] [--help] [--interactive] [--no-prompt] [--no-read-prompt] [--extended-register] [-e expr] [--expression=expr...] [-f file...] [--file=file...] [file...]

DESCRIPTION

dc(1) is an arbitrary-precision calculator. It uses a stack (reverse Polish notation) to store numbers and results of computations. Arithmetic operations pop arguments off of the stack and push the results.

If no files are given on the command-line, then dc(1) reads from stdin (see the STDIN section). Otherwise, those files are processed, and dc(1) will then exit.

If a user wants to set up a standard environment, they can use DC_ENV_ARGS (see the ENVIRONMENT VARIABLES section). For example, if a user wants the scale always set to 10, they can set DC_ENV_ARGS to -e 10k, and this dc(1) will always start with a scale of 10.

OPTIONS

The following are the options that dc(1) accepts.

-h, --help

Prints a usage message and quits.

-v, -V, --version

Print the version information (copyright header) and exit.

-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.

-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 dc(1). Most of those users would want to put this option in DC_ENV_ARGS.

These options override the DC_PROMPT and DC_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 dc(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 dc(1) scripts that prompt for user input.

This option does not disable the regular prompt because the read prompt is only used when the ? command is used.

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

This is a non-portable extension.

-x --extended-register

Enables extended register mode. See the Extended Register Mode subsection of the REGISTERS section for more information.

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.

-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 DC_ENV_ARGS, see the ENVIRONMENT VARIABLES section), then after processing all expressions and files, dc(1) will exit, unless - (stdin) was given as an argument at least once to -f or --file, whether on the command-line or in DC_ENV_ARGS. However, if any other -e, --expression, -f, or --file arguments are given after -f- or equivalent is given, dc(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 DC_ENV_ARGS, see the ENVIRONMENT VARIABLES section), then after processing all expressions and files, dc(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, dc(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 are given on the command-line and no files or expressions are given by the -f, --file, -e, or --expression options, then dc(1) read from stdin.

However, there is a caveat to this.

First, stdin is evaluated a line at a time. The only exception to this is if a string has been finished, but not ended. This means that, except for escaped brackets, all brackets must be balanced before dc(1) parses and executes.

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

If there are scripts that depend on the behavior of other dc(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 dc(1) implementations, this dc(1) will issue a fatal error (see the EXIT STATUS section) if it cannot write to stderr, so if stderr is closed, as in dc 2>&-, it will quit with an error. This is done so that dc(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 dc(1) implementations, it is recommended that those scripts be changed to redirect stderr to /dev/null.

SYNTAX

Each item in the input source code, either a number (see the NUMBERS section) or a command (see the COMMANDS section), is processed and executed, in order. Input is processed immediately when entered.

ibase is a register (see the REGISTERS section) that determines how to interpret constant numbers. It is the "input" base, or the number base used for interpreting input numbers. ibase is initially 10. The max allowable value for ibase is 16. The min allowable value for ibase is 2. The max allowable value for ibase can be queried in dc(1) programs with the T command.

obase is a register (see the REGISTERS section) that determines 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 DC_BASE_MAX and can be queried with the U command. 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 register (see the REGISTERS section) that sets the precision of any operations (with exceptions). scale is initially 0. scale cannot be negative. The max allowable value for scale can be queried in dc(1) programs with the V command.

Comments

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

NUMBERS

Numbers are strings made up of digits, uppercase letters up to F, and at most 1 period for a radix. Numbers can have up to DC_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 F alone always equals decimal 15.

COMMANDS

The valid commands are listed below.

Printing

These commands are used for printing.

p

Prints the value on top of the stack, whether number or string, and prints a newline after.

This does not alter the stack.

n

Prints the value on top of the stack, whether number or string, and pops it off of the stack.

P

Pops a value off the stack.

If the value is a number, it is truncated and the absolute value of the result is printed as though obase is 256 and each digit is interpreted as an 8-bit ASCII character, making it a byte stream.

If the value is a string, it is printed without a trailing newline.

This is a non-portable extension.

f

Prints the entire contents of the stack, in order from newest to oldest, without altering anything.

Users should use this command when they get lost.

Arithmetic

These are the commands used for arithmetic.

+

The top two values are popped off the stack, added, and the result is pushed onto the stack. The scale of the result is equal to the max scale of both operands.

-

The top two values are popped off the stack, subtracted, and the result is pushed onto the stack. The scale of the result is equal to the max scale of both operands.

*

The top two values are popped off the stack, multiplied, and the result is pushed onto the stack. 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 top two values are popped off the stack, divided, and the result is pushed onto the stack. The scale of the result is equal to scale.

The first value popped off of the stack must be non-zero.

%

The top two values are popped off the stack, remaindered, and the result is pushed onto the stack.

Remaindering is equivalent to 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 first value popped off of the stack must be non-zero.

~

The top two values are popped off the stack, divided and remaindered, and the results (divided first, remainder second) are pushed onto the stack. This is equivalent to x y / x y % except that x and y are only evaluated once.

The first value popped off of the stack must be non-zero.

This is a non-portable extension.

^

The top two values are popped off the stack, the second is raised to the power of the first, and the result is pushed onto the stack. The scale of the result is equal to scale.

The first value popped off of the stack must be an integer, and if that value is negative, the second value popped off of the stack must be non-zero.

v

The top value is popped off the stack, its square root is computed, and the result is pushed onto the stack. The scale of the result is equal to scale.

The value popped off of the stack must be non-negative.

_

If this command immediately precedes a number (i.e., no spaces or other commands), then that number is input as a negative number.

Otherwise, the top value on the stack is popped and copied, and the copy is negated and pushed onto the stack. This behavior without a number is a non-portable extension.

b

The top value is popped off the stack, and if it is zero, it is pushed back onto the stack. Otherwise, its absolute value is pushed onto the stack.

This is a non-portable extension.

|

The top three values are popped off the stack, a modular exponentiation is computed, and the result is pushed onto the stack.

The first value popped is used as the reduction modulus and must be an integer and non-zero. The second value popped is used as the exponent and must be an integer and non-negative. The third value popped is the base and must be an integer.

This is a non-portable extension.

G

The top two values are popped off of the stack, they are compared, and a 1 is pushed if they are equal, or 0 otherwise.

This is a non-portable extension.

N

The top value is popped off of the stack, and if it a 0, a 1 is pushed; otherwise, a 0 is pushed.

This is a non-portable extension.

(

The top two values are popped off of the stack, they are compared, and a 1 is pushed if the first is less than the second, or 0 otherwise.

This is a non-portable extension.

{

The top two values are popped off of the stack, they are compared, and a 1 is pushed if the first is less than or equal to the second, or 0 otherwise.

This is a non-portable extension.

)

The top two values are popped off of the stack, they are compared, and a 1 is pushed if the first is greater than the second, or 0 otherwise.

This is a non-portable extension.

}

The top two values are popped off of the stack, they are compared, and a 1 is pushed if the first is greater than or equal to the second, or 0 otherwise.

This is a non-portable extension.

M

The top two values are popped off of the stack. If they are both non-zero, a 1 is pushed onto the stack. If either of them is zero, or both of them are, then a 0 is pushed onto the stack.

This is like the && operator in bc(1), and it is not a short-circuit operator.

This is a non-portable extension.

m

The top two values are popped off of the stack. If at least one of them is non-zero, a 1 is pushed onto the stack. If both of them are zero, then a 0 is pushed onto the stack.

This is like the || operator in bc(1), and it is not a short-circuit operator.

This is a non-portable extension.

Stack Control

These commands control the stack.

c

Removes all items from ("clears") the stack.

d

Copies the item on top of the stack ("duplicates") and pushes the copy onto the stack.

r

Swaps ("reverses") the two top items on the stack.

R

Pops ("removes") the top value from the stack.

Register Control

These commands control registers (see the REGISTERS section).

sr

Pops the value off the top of the stack and stores it into register r.

lr

Copies the value in register r and pushes it onto the stack. This does not alter the contents of r.

Sr

Pops the value off the top of the (main) stack and pushes it onto the stack of register r. The previous value of the register becomes inaccessible.

Lr

Pops the value off the top of the stack for register r and push it onto the main stack. The previous value in the stack for register r, if any, is now accessible via the lr command.

Parameters

These commands control the values of ibase, obase, and scale. Also see the SYNTAX section.

i

Pops the value off of the top of the stack and uses it to set ibase, which must be between 2 and 16, inclusive.

If the value on top of the stack has any scale, the scale is ignored.

o

Pops the value off of the top of the stack and uses it to set obase, which must be between 2 and DC_BASE_MAX, inclusive (see the LIMITS section).

If the value on top of the stack has any scale, the scale is ignored.

k

Pops the value off of the top of the stack and uses it to set scale, which must be non-negative.

If the value on top of the stack has any scale, the scale is ignored.

I

Pushes the current value of ibase onto the main stack.

O

Pushes the current value of obase onto the main stack.

K

Pushes the current value of scale onto the main stack.

T

Pushes the maximum allowable value of ibase onto the main stack.

This is a non-portable extension.

U

Pushes the maximum allowable value of obase onto the main stack.

This is a non-portable extension.

V

Pushes the maximum allowable value of scale onto the main stack.

This is a non-portable extension.

Strings

The following commands control strings.

dc(1) can work with both numbers and strings, and registers (see the REGISTERS section) can hold both strings and numbers. dc(1) always knows whether the contents of a register are a string or a number.

While arithmetic operations have to have numbers, and will print an error if given a string, other commands accept strings.

Strings can also be executed as macros. For example, if the string [1pR] is executed as a macro, then the code 1pR is executed, meaning that the 1 will be printed with a newline after and then popped from the stack.

[characters]

Makes a string containing characters and pushes it onto the stack.

If there are brackets ([ and ]) in the string, then they must be balanced. Unbalanced brackets can be escaped using a backslash (\) character.

If there is a backslash character in the string, the character after it (even another backslash) is put into the string verbatim, but the (first) backslash is not.

a

The value on top of the stack is popped.

If it is a number, it is truncated and its absolute value is taken. The result mod 256 is calculated. If that result is 0, push an empty string; otherwise, push a one-character string where the character is the result of the mod interpreted as an ASCII character.

If it is a string, then a new string is made. If the original string is empty, the new string is empty. If it is not, then the first character of the original string is used to create the new string as a one-character string. The new string is then pushed onto the stack.

This is a non-portable extension.

x

Pops a value off of the top of the stack.

If it is a number, it is pushed back onto the stack.

If it is a string, it is executed as a macro.

This behavior is the norm whenever a macro is executed, whether by this command or by the conditional execution commands below.

>r

Pops two values off of the stack that must be numbers and compares them. If the first value is greater than the second, then the contents of register r are executed.

For example, 0 1>a will execute the contents of register a, and 1 0>a will not.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

>res

Like the above, but will execute register s if the comparison fails.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

This is a non-portable extension.

!>r

Pops two values off of the stack that must be numbers and compares them. If the first value is not greater than the second (less than or equal to), then the contents of register r are executed.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

!>res

Like the above, but will execute register s if the comparison fails.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

This is a non-portable extension.

<r

Pops two values off of the stack that must be numbers and compares them. If the first value is less than the second, then the contents of register r are executed.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

<res

Like the above, but will execute register s if the comparison fails.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

This is a non-portable extension.

!<r

Pops two values off of the stack that must be numbers and compares them. If the first value is not less than the second (greater than or equal to), then the contents of register r are executed.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

!<res

Like the above, but will execute register s if the comparison fails.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

This is a non-portable extension.

=r

Pops two values off of the stack that must be numbers and compares them. If the first value is equal to the second, then the contents of register r are executed.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

=res

Like the above, but will execute register s if the comparison fails.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

This is a non-portable extension.

!=r

Pops two values off of the stack that must be numbers and compares them. If the first value is not equal to the second, then the contents of register r are executed.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

!=res

Like the above, but will execute register s if the comparison fails.

If either or both of the values are not numbers, dc(1) will raise an error and reset (see the RESET section).

This is a non-portable extension.

?

Reads a line from the stdin and executes it. This is to allow macros to request input from users.

q

During execution of a macro, this exits the execution of that macro and the execution of the macro that executed it. If there are no macros, or only one macro executing, dc(1) exits.

Q

Pops a value from the stack which must be non-negative and is used the number of macro executions to pop off of the execution stack. If the number of levels to pop is greater than the number of executing macros, dc(1) exits.

,

Pushes the depth of the execution stack onto the stack. The execution stack is the stack of string executions. The number that is pushed onto the stack is exactly as many as is needed to make dc(1) exit with the Q command, so the sequence ,Q will make dc(1) exit.

Status

These commands query status of the stack or its top value.

Z

Pops a value off of the stack.

If it is a number, calculates the number of significant decimal digits it has and pushes the result. It will push 1 if the argument is 0 with no decimal places.

If it is a string, pushes the number of characters the string has.

X

Pops a value off of the stack.

If it is a number, pushes the scale of the value onto the stack.

If it is a string, pushes 0.

z

Pushes the current depth of the stack (before execution of this command) onto the stack.

yr

Pushes the current stack depth of the register r onto the main stack.

Because each register has a depth of 1 (with the value 0 in the top item) when dc(1) starts, dc(1) requires that each register's stack must always have at least one item; dc(1) will give an error and reset otherwise (see the RESET section). This means that this command will never push 0.

This is a non-portable extension.

Arrays

These commands manipulate arrays.

:r

Pops the top two values off of the stack. The second value will be stored in the array r (see the REGISTERS section), indexed by the first value.

;r

Pops the value on top of the stack and uses it as an index into the array r. The selected value is then pushed onto the stack.

Yr

Pushes the length of the array r onto the stack.

This is a non-portable extension.

Global Settings

These commands retrieve global settings. These are the only commands that require multiple specific characters, and all of them begin with the letter g. Only the characters below are allowed after the character g; any other character produces a parse error (see the ERRORS section).

gl

Pushes the line length set by DC_LINE_LENGTH (see the ENVIRONMENT VARIABLES section) onto the stack.

gz

Pushes 0 onto the stack if the leading zero setting has not been enabled with the -z or --leading-zeroes options (see the OPTIONS section), non-zero otherwise.

REGISTERS

Registers are names that can store strings, numbers, and arrays. (Number/string registers do not interfere with array registers.)

Each register is also its own stack, so the current register value is the top of the stack for the register. All registers, when first referenced, have one value (0) in their stack, and it is a runtime error to attempt to pop that item off of the register stack.

In non-extended register mode, a register name is just the single character that follows any command that needs a register name. The only exceptions are: a newline ('\n') and a left bracket ('['); it is a parse error for a newline or a left bracket to be used as a register name.

Extended Register Mode

Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited amounts of registers, if extended register mode is enabled.

If extended register mode is enabled (-x or --extended-register command-line arguments are given), then normal single character registers are used unless the character immediately following a command that needs a register name is a space (according to isspace()) and not a newline ('\n').

In that case, the register name is found according to the regex [a-z][a-z0-9_]* (like bc(1) identifiers), and it is a parse error if the next non-space characters do not match that regex.

RESET

When dc(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 macros 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 macros returned) is skipped.

Thus, when dc(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.

PERFORMANCE

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

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

In addition, this dc(1) uses an even larger integer for overflow checking. This integer type depends on the value of DC_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 dc(1):

DC_LONG_BIT

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

DC_BASE_DIGS

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

DC_BASE_POW

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

DC_OVERFLOW_MAX

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

DC_BASE_MAX

The maximum output base. Set at DC_BASE_POW.

DC_DIM_MAX

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

DC_SCALE_MAX

The maximum scale. Set at DC_OVERFLOW_MAX-1.

DC_STRING_MAX

The maximum length of strings. Set at DC_OVERFLOW_MAX-1.

DC_NAME_MAX

The maximum length of identifiers. Set at DC_OVERFLOW_MAX-1.

DC_NUM_MAX

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

Exponent

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

Number of vars

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

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

dc(1) recognizes the following environment variables:

DC_ENV_ARGS

This is another way to give command-line arguments to dc(1). They should be in the same format as all other command-line arguments. These are always processed first, so any files given in DC_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 dc(1) runs. Another use would be to use the -e option to set scale to a value other than 0.

The code that parses DC_ENV_ARGS will correctly handle quoted arguments, but it does not understand escape sequences. For example, the string "/home/gavin/some dc file.dc" will be correctly parsed, but the string "/home/gavin/some "dc" file.dc" 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 'dc' file.dc", and vice versa if you have a file with double quotes. However, handling a file with both kinds of quotes in DC_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.

DC_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), dc(1) will output lines to that length, including the backslash newline combo. 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.

DC_SIGINT_RESET

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

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

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

DC_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 dc(1) use TTY mode, and zero makes dc(1) not use TTY mode.

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

DC_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 dc(1) use a prompt, and zero or a non-integer makes dc(1) not use a prompt. If this environment variable does not exist and DC_TTY_MODE does, then the value of the DC_TTY_MODE environment variable is used.

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

EXIT STATUS

dc(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.

2

A parse error occurred.

Parse errors include unexpected EOF, using an invalid character, failing to find the end of a string or comment, and using a token where it is invalid.

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 (including attempting to execute a number), and attempting an operation when the stack has too few elements.

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 (dc(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, dc(1) always exits and returns 4, no matter what mode dc(1) is in.

The other statuses will only be returned when dc(1) is not in interactive mode (see the INTERACTIVE MODE section), since dc(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 dc(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

Like bc(1), dc(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, dc(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. dc(1) may also reset on SIGINT instead of exit, depending on the contents of, or default for, the DC_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, dc(1) can turn on TTY mode, subject to some settings.

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

If the environment variable DC_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, and interactive mode requires only stdin and stdout to be connected to a terminal.

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: DC_PROMPT (see the ENVIRONMENT VARIABLES section).

If the environment variable DC_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 DC_PROMPT does not exist, the prompt can be enabled or disabled with the DC_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 dc(1) to do one of two things.

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

However, if dc(1) is in interactive mode, and the DC_SIGINT_RESET or its default is an integer and non-zero, then dc(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 dc(1) is processing input from stdin in interactive mode, it will ask for more input. If dc(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 dc(1) as it is executing a file, it can seem as though dc(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 dc(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 dc(1) to clean up and exit, and it uses the default handler for all other signals.

SEE ALSO

bc(1)

STANDARDS

The dc(1) utility operators are compliant with the operators in the bc(1) IEEE Std 1003.1-2017 (“POSIX.1-2017”) specification.

BUGS

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

AUTHOR

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