DC(1)

Name

dc - arbitrary-precision reverse-Polish notation calculator

SYNOPSIS

dc [-hiPvVx] [--version] [--help] [--interactive] [--no-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 as extra arguments (i.e., not as -f or --file arguments), then dc(1) reads from stdin. Otherwise, those files are processed, and dc(1) will then exit.

This is different from the dc(1) on OpenBSD and possibly other dc(1) implementations, where -e (--expression) and -f (--file) arguments cause dc(1) to execute them and exit. The reason for this is that this dc(1) allows users to set arguments in the environment variable DC_ENV_ARGS (see the ENVIRONMENT VARIABLES section). Any expressions given on the command-line should be used to set up a standard environment. 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.

If users want to have dc(1) exit after processing all input from -e and -f arguments (and their equivalents), then they can just simply add -e q as the last command-line argument or define the environment variable DC_EXPR_EXIT.

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.

-P, --no-prompt
    This option is a no-op.

    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.

-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, dc(1) will exit, unless - (stdin) was given as an argument at least once to -f or --file.

    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, 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 that, bc(1) will give a fatal error and exit.

    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 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 0. If obase is 0, values are output in scientific notation, and if obase is 1, values are output in engineering notation. Otherwise, values are output in the specified base.

Outputting in scientific and engineering notations are non-portable extensions.

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.

seed is a register containing the current seed for the pseudo-random number generator. If the current value of seed is queried and stored, then if it is assigned to seed later, the pseudo-random number generator is guaranteed to produce the same sequence of pseudo-random numbers that were generated after the value of seed was first queried.

Multiple values assigned to seed can produce the same sequence of pseudo-random numbers. Likewise, when a value is assigned to seed, it is not guaranteed that querying seed immediately after will return the same value. In addition, the value of seed will change after any call to the ' command or the " command that does not get receive a value of 0 or 1. The maximum integer returned by the ' command can be queried with the W command.

Note: The values returned by the pseudo-random number generator with the ' and " commands are guaranteed to NOT be cryptographically secure. This is a consequence of using a seeded pseudo-random number generator. However, they are guaranteed to be reproducible with identical seed values.

The pseudo-random number generator, seed, and all associated operations are non-portable extensions.

  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.

In addition, dc(1) accepts numbers in scientific notation. These have the form <number>e<integer>. The power (the portion after the e) must be an integer. An example is 1.89237e9, which is equal to 1892370000. Negative exponents are also allowed, so 4.2890e_3 is equal to 0.0042890.

WARNING: Both the number and the exponent in scientific notation are interpreted according to the current ibase, but the number is still multiplied by 10^exponent regardless of the current ibase. For example, if ibase is 16 and dc(1) is given the number string FFeA, the resulting decimal number will be 2550000000000, and if dc(1) is given the number string 10e_4, the resulting decimal number will be 0.0016.

Accepting input as scientific notation is a non-portable extension.

COMMANDS

The valid commands are listed below.

  Printing

These commands are used for printing.

Note that both scientific notation and engineering notation are available for printing numbers. Scientific notation is activated by assigning 0 to obase using 0o, and engineering notation is activated by assigning 1 to obase using 1o. To deactivate them, just assign a different value to obase.

Printing numbers in scientific notation and/or engineering notation is a non-portable extension.

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 UCHAR_MAX+1 and each digit is interpreted as an 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 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.

$   The top value is popped off the stack and copied, and the copy is truncated and pushed onto the stack.

    This is a non-portable extension.

@   The top two values are popped off the stack, and the precision of the second is set to the value of the first, whether by truncation or extension.

    The first value popped off of the stack must be an integer and non-negative.

    This is a non-portable extension.

H   The top two values are popped off the stack, and the second is shifted left (radix shifted right) to the value of the first.

    The first value popped off of the stack must be an integer and non-negative.

    This is a non-portable extension.

h   The top two values are popped off the stack, and the second is shifted right (radix shifted left) to the value of the first.

    The first value popped off of the stack must be an integer and non-negative.

    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.

  Pseudo-Random Number Generator

dc(1) has a built-in pseudo-random number generator. These commands query the pseudo-random number generator. (See Parameters for more information about the seed value that controls the pseudo-random number generator.)

The pseudo-random number generator is guaranteed to NOT be cryptographically secure.

'   Generates an integer between 0 and DC_RAND_MAX, inclusive (see the LIMITS section).

    The generated integer is made as unbiased as possible, subject to the limitations of the pseudo-random number generator.

    This is a non-portable extension.

"   Pops a value off of the stack, which is used as an exclusive upper bound on the integer that will be generated. If the bound is negative or is a non-integer, an error is raised, and dc(1) resets (see the RESET section) while seed remains unchanged. If the bound is larger than DC_RAND_MAX, the higher bound is honored by generating several pseudo-random integers, multiplying them by appropriate powers of DC_RAND_MAX+1, and adding them together. Thus, the size of integer that can be generated with this command is unbounded. Using this command will change the value of seed, unless the operand is 0 or 1. In that case, 0 is pushed onto the stack, and seed is not changed.

    The generated integer is made as unbiased as possible, subject to the limitations of the pseudo-random number generator.

    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, scale, and seed. 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 0 and DC_BASE_MAX, inclusive (see the LIMITS section and the NUMBERS 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.

j   Pops the value off of the top of the stack and uses it to set seed. The meaning of seed is dependent on the current pseudo-random number generator but is guaranteed to not change except for new major versions.

    The scale and sign of the value may be significant.

    If a previously used seed value is used again, the pseudo-random number generator is guaranteed to produce the same sequence of pseudo-random numbers as it did when the seed value was previously used.

    The exact value assigned to seed is not guaranteed to be returned if the J command is used. However, if seed does return a different value, both values, when assigned to seed, are guaranteed to produce the same sequence of pseudo-random numbers. This means that certain values assigned to seed will not produce unique sequences of pseudo-random numbers.

    There is no limit to the length (number of significant decimal digits) or scale of the value that can be assigned to seed.

    This is a non-portable extension.

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.

J   Pushes the current value of seed onto the main stack.

    This is a non-portable extension.

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.

W   Pushes the maximum (inclusive) integer that can be generated with the ' pseudo-random number generator command.

    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 UCHAR_MAX+1 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.

  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.

    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 stack depth (before execution of this command).

  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.

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.

In non-extended register mode, a register name is just the single character that follows any command that needs a register name. The only exception is a newline ('\n'); it is a parse error for a newline 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.

DC_RAND_MAX
    The maximum integer (inclusive) returned by the ' command, if dc(1). Set at 2^DC_LONG_BIT-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 'bc' file.bc", 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.

DC_EXPR_EXIT
    If this variable exists (no matter the contents), dc(1) will exit immediately after executing expressions and files given by the -e and/or -f command-line options (and any equivalents).

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, using a negative number as a bound for the pseudo-random number generator, 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 (^), places (@), left shift (H), and right shift (h) operators.

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 ibase, obase, or scale; give a bad expression to a read() call, calling read() inside of a read() call, type errors, 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 cases.

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.

TTY MODE

If stdin, stdout, and stderr are all connected to a TTY, dc(1) turns on "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 dc(1) to stop execution of the current input. If dc(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 dc(1) is processing input from stdin in TTY mode, it will ask for more input. If dc(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 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”) (https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html) specification.

BUGS

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

AUTHOR

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