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dc - arbitrary-precision reverse-Polish notation calculator

\f[B]dc\f[] [\f[B]-hiPvVx\f[]] [\f[B]--version\f[]] [\f[B]--help\f[]] [\f[B]--interactive\f[]] [\f[B]--no-prompt\f[]] [\f[B]--extended-register\f[]] [\f[B]-e\f[] \f[I]expr\f[]] [\f[B]--expression\f[]=\f[I]expr\f[]...] [\f[B]-f\f[] \f[I]file\f[]...] [\f[B]-file\f[]=\f[I]file\f[]...] [\f[I]file\f[]...]

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[B]-f\f[] or \f[B]--file\f[] arguments), then dc(1) reads from \f[B]stdin\f[]. 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 \f[B]-e\f[] (\f[B]--expression\f[]) and \f[B]-f\f[] (\f[B]--file\f[]) 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 \f[B]DC_ENV_ARGS\f[] (see the \f[B]ENVIRONMENT VARIABLES\f[] section). Any expressions given on the command-line should be used to set up a standard environment. For example, if a user wants the \f[B]scale\f[] always set to \f[B]10\f[], they can set \f[B]DC_ENV_ARGS\f[] to \f[B]-e 10k\f[], and this dc(1) will always start with a \f[B]scale\f[] of \f[B]10\f[].

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

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

\f[B]-h\f[], \f[B]--help\f[] Prints a usage message and quits.

\f[B]-v\f[], \f[B]-V\f[], \f[B]--version\f[] Print the version information (copyright header) and exit.

\f[B]-i\f[], \f[B]--interactive\f[] Forces interactive mode. (See the \f[B]INTERACTIVE MODE\f[] section.)

\f[B]-P\f[], \f[B]--no-prompt\f[] Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode. See the \f[B]TTY MODE\f[] 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 \f[B]DC_ENV_ARGS\f[].

\f[B]-x\f[] \f[B]--extended-register\f[] Enables extended register mode. See the \f[I]Extended Register Mode\f[] subsection of the \f[B]REGISTERS\f[] section for more information.

\f[B]-e\f[] \f[I]expr\f[], \f[B]--expression\f[]=\f[I]expr\f[] Evaluates \f[I]expr\f[]. 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.

\f[B]-f\f[] \f[I]file\f[], \f[B]--file\f[]=\f[I]file\f[] Reads in \f[I]file\f[] and evaluates it, line by line, as though it were read through \f[B]stdin\f[]. If expressions are also given (see above), the expressions are evaluated in the order given.

All long options are \f[B]non-portable extensions\f[].

Any non-error output is written to \f[B]stdout\f[].

\f[B]Note\f[]: Unlike other dc(1) implementations, this dc(1) will issue a fatal error (see the \f[B]EXIT STATUS\f[] section) if it cannot write to \f[B]stdout\f[], so if \f[B]stdout\f[] is closed, as in \f[B]dc >&-\f[], it will quit with an error. This is done so that dc(1) can report problems when \f[B]stdout\f[] 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 \f[B]stdout\f[] to \f[B]/dev/null\f[].

Any error output is written to \f[B]stderr\f[].

\f[B]Note\f[]: Unlike other dc(1) implementations, this dc(1) will issue a fatal error (see the \f[B]EXIT STATUS\f[] section) if it cannot write to \f[B]stderr\f[], so if \f[B]stderr\f[] is closed, as in \f[B]dc 2>&-\f[], it will quit with an error. This is done so that dc(1) can exit with an error code when \f[B]stderr\f[] 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 \f[B]stderr\f[] to \f[B]/dev/null\f[].

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

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

\f[B]obase\f[] is a register (see the \f[B]REGISTERS\f[] section) that determines how to output results. It is the "output" base, or the number base used for outputting numbers. \f[B]obase\f[] is initially \f[B]10\f[]. The max allowable value for \f[B]obase\f[] is \f[B]DC_BASE_MAX\f[] and can be queried with the \f[B]U\f[] command. The min allowable value for \f[B]obase\f[] is \f[B]0\f[]. If \f[B]obase\f[] is \f[B]0\f[], values are output in scientific notation, and if \f[B]obase\f[] is \f[B]1\f[], values are output in engineering notation. Otherwise, values are output in the specified base.

Outputting in scientific and engineering notations are \f[B]non-portable extensions\f[].

The \f[I]scale\f[] of an expression is the number of digits in the result of the expression right of the decimal point, and \f[B]scale\f[] is a register (see the \f[B]REGISTERS\f[] section) that sets the precision of any operations (with exceptions). \f[B]scale\f[] is initially \f[B]0\f[]. \f[B]scale\f[] cannot be negative. The max allowable value for \f[B]scale\f[] can be queried in dc(1) programs with the \f[B]V\f[] command.

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

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

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

The pseudo-random number generator, \f[B]seed\f[], and all associated operations are \f[B]non-portable extensions\f[].

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

Numbers are strings made up of digits, uppercase letters up to \f[B]F\f[], and at most \f[B]1\f[] period for a radix. Numbers can have up to \f[B]DC_NUM_MAX\f[] digits. Uppercase letters are equal to \f[B]9\f[] + their position in the alphabet (i.e., \f[B]A\f[] equals \f[B]10\f[], or \f[B]9+1\f[]). If a digit or letter makes no sense with the current value of \f[B]ibase\f[], they are set to the value of the highest valid digit in \f[B]ibase\f[].

Single-character numbers (i.e., \f[B]A\f[] alone) take the value that they would have if they were valid digits, regardless of the value of \f[B]ibase\f[]. This means that \f[B]A\f[] alone always equals decimal \f[B]10\f[] and \f[B]F\f[] alone always equals decimal \f[B]15\f[].

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

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

Accepting input as scientific notation is a \f[B]non-portable extension\f[].

The valid commands are listed below.

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 \f[B]0\f[] to \f[B]obase\f[] using \f[B]0o\f[], and engineering notation is activated by assigning \f[B]1\f[] to \f[B]obase\f[] using \f[B]1o\f[]. To deactivate them, just assign a different value to \f[B]obase\f[].

Printing numbers in scientific notation and/or engineering notation is a \f[B]non-portable extension\f[].

\f[B]p\f[] Prints the value on top of the stack, whether number or string, and prints a newline after.

\f[B]n\f[] Prints the value on top of the stack, whether number or string, and pops it off of the stack.

\f[B]P\f[] Pops a value off the stack.

\f[B]f\f[] Prints the entire contents of the stack, in order from newest to oldest, without altering anything.

These are the commands used for arithmetic.

\f[B]+\f[] The top two values are popped off the stack, added, and the result is pushed onto the stack. The \f[I]scale\f[] of the result is equal to the max \f[I]scale\f[] of both operands.

\f[B]-\f[] The top two values are popped off the stack, subtracted, and the result is pushed onto the stack. The \f[I]scale\f[] of the result is equal to the max \f[I]scale\f[] of both operands.

\f[B]*\f[] The top two values are popped off the stack, multiplied, and the result is pushed onto the stack. If \f[B]a\f[] is the \f[I]scale\f[] of the first expression and \f[B]b\f[] is the \f[I]scale\f[] of the second expression, the \f[I]scale\f[] of the result is equal to \f[B]min(a+b,max(scale,a,b))\f[] where \f[B]min()\f[] and \f[B]max()\f[] return the obvious values.

\f[B]/\f[] The top two values are popped off the stack, divided, and the result is pushed onto the stack. The \f[I]scale\f[] of the result is equal to \f[B]scale\f[].

\f[B]%\f[] The top two values are popped off the stack, remaindered, and the result is pushed onto the stack.

\f[B]~\f[] 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 \f[B]x y / x y %\f[] except that \f[B]x\f[] and \f[B]y\f[] are only evaluated once.

\f[B]^\f[] 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.

\f[B]v\f[] The top value is popped off the stack, its square root is computed, and the result is pushed onto the stack. The \f[I]scale\f[] of the result is equal to \f[B]scale\f[].

\f[B]_\f[] If this command \f[I]immediately\f[] precedes a number (i.e., no spaces or other commands), then that number is input as a negative number.

\f[B]b\f[] 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.

\f[B]|\f[] The top three values are popped off the stack, a modular exponentiation is computed, and the result is pushed onto the stack.

\f[B]$\f[] The top value is popped off the stack and copied, and the copy is truncated and pushed onto the stack.

\f[B]\@\f[] 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.

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

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

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

\f[B]N\f[] The top value is popped off of the stack, and if it a \f[B]0\f[], a \f[B]1\f[] is pushed; otherwise, a \f[B]0\f[] is pushed.

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

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

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

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

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

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

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 \f[B]seed\f[] value that controls the pseudo-random number generator.)

The pseudo-random number generator is guaranteed to \f[B]NOT\f[] be cryptographically secure.

\f[B]\[aq]\f[] Generates an integer between 0 and \f[B]DC_RAND_MAX\f[], inclusive (see the \f[B]LIMITS\f[] section).

\f[B]"\f[] Pops a value off of the stack, which is used as an \f[B]exclusive\f[] 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 \f[B]RESET\f[] section) while \f[B]seed\f[] remains unchanged. If the bound is larger than \f[B]DC_RAND_MAX\f[], the higher bound is honored by generating several pseudo-random integers, multiplying them by appropriate powers of \f[B]DC_RAND_MAX+1\f[], 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 \f[B]seed\f[], unless the operand is \f[B]0\f[] or \f[B]1\f[]. In that case, \f[B]0\f[] is pushed onto the stack, and \f[B]seed\f[] is \f[I]not\f[] changed.

These commands control the stack.

\f[B]c\f[] Removes all items from ("clears") the stack.

\f[B]d\f[] Copies the item on top of the stack ("duplicates") and pushes the copy onto the stack.

\f[B]r\f[] Swaps ("reverses") the two top items on the stack.

\f[B]R\f[] Pops ("removes") the top value from the stack.

These commands control registers (see the \f[B]REGISTERS\f[] section).

\f[B]s\f[]\f[I]r\f[] Pops the value off the top of the stack and stores it into register \f[I]r\f[].

\f[B]l\f[]\f[I]r\f[] Copies the value in register \f[I]r\f[] and pushes it onto the stack. This does not alter the contents of \f[I]r\f[].

\f[B]S\f[]\f[I]r\f[] Pops the value off the top of the (main) stack and pushes it onto the stack of register \f[I]r\f[]. The previous value of the register becomes inaccessible.

\f[B]L\f[]\f[I]r\f[] Pops the value off the top of the stack for register \f[I]r\f[] and push it onto the main stack. The previous value in the stack for register \f[I]r\f[], if any, is now accessible via the \f[B]l\f[]\f[I]r\f[] command.

These commands control the values of \f[B]ibase\f[], \f[B]obase\f[], \f[B]scale\f[], and \f[B]seed\f[]. Also see the \f[B]SYNTAX\f[] section.

\f[B]i\f[] Pops the value off of the top of the stack and uses it to set \f[B]ibase\f[], which must be between \f[B]2\f[] and \f[B]16\f[], inclusive.

\f[B]o\f[] Pops the value off of the top of the stack and uses it to set \f[B]obase\f[], which must be between \f[B]0\f[] and \f[B]DC_BASE_MAX\f[], inclusive (see the \f[B]LIMITS\f[] section and the \f[B]NUMBERS\f[] section).

\f[B]k\f[] Pops the value off of the top of the stack and uses it to set \f[B]scale\f[], which must be non-negative.

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

\f[B]I\f[] Pushes the current value of \f[B]ibase\f[] onto the main stack.

\f[B]O\f[] Pushes the current value of \f[B]obase\f[] onto the main stack.

\f[B]K\f[] Pushes the current value of \f[B]scale\f[] onto the main stack.

\f[B]J\f[] Pushes the current value of \f[B]seed\f[] onto the main stack.

\f[B]T\f[] Pushes the maximum allowable value of \f[B]ibase\f[] onto the main stack.

\f[B]U\f[] Pushes the maximum allowable value of \f[B]obase\f[] onto the main stack.

\f[B]V\f[] Pushes the maximum allowable value of \f[B]scale\f[] onto the main stack.

\f[B]W\f[] Pushes the maximum (inclusive) integer that can be generated with the \f[B]\[aq]\f[] pseudo-random number generator command.

The following commands control strings.

dc(1) can work with both numbers and strings, and registers (see the \f[B]REGISTERS\f[] 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 \f[B][1pR]\f[] is executed as a macro, then the code \f[B]1pR\f[] is executed, meaning that the \f[B]1\f[] will be printed with a newline after and then popped from the stack.

\f[B][\f[]\f[I]characters\f[]\f[B]]\f[] Makes a string containing \f[I]characters\f[] and pushes it onto the stack.

\f[B]a\f[] The value on top of the stack is popped.

\f[B]x\f[] Pops a value off of the top of the stack.

\f[B]>\f[]\f[I]r\f[] 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 \f[I]r\f[] are executed.

\f[B]>\f[]\f[I]r\f[]\f[B]e\f[]\f[I]s\f[] Like the above, but will execute register \f[I]s\f[] if the comparison fails.

\f[B]!>\f[]\f[I]r\f[] 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 \f[I]r\f[] are executed.

\f[B]!>\f[]\f[I]r\f[]\f[B]e\f[]\f[I]s\f[] Like the above, but will execute register \f[I]s\f[] if the comparison fails.

\f[B]<\f[]\f[I]r\f[] 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 \f[I]r\f[] are executed.

\f[B]<\f[]\f[I]r\f[]\f[B]e\f[]\f[I]s\f[] Like the above, but will execute register \f[I]s\f[] if the comparison fails.

\f[B]!<\f[]\f[I]r\f[] 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 \f[I]r\f[] are executed.

\f[B]!<\f[]\f[I]r\f[]\f[B]e\f[]\f[I]s\f[] Like the above, but will execute register \f[I]s\f[] if the comparison fails.

\f[B]=\f[]\f[I]r\f[] 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 \f[I]r\f[] are executed.

\f[B]=\f[]\f[I]r\f[]\f[B]e\f[]\f[I]s\f[] Like the above, but will execute register \f[I]s\f[] if the comparison fails.

\f[B]!=\f[]\f[I]r\f[] 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 \f[I]r\f[] are executed.

\f[B]!=\f[]\f[I]r\f[]\f[B]e\f[]\f[I]s\f[] Like the above, but will execute register \f[I]s\f[] if the comparison fails.

\f[B]?\f[] Reads a line from the \f[B]stdin\f[] and executes it. This is to allow macros to request input from users.

\f[B]q\f[] 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.

\f[B]Q\f[] 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.

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

\f[B]Z\f[] Pops a value off of the stack.

\f[B]X\f[] Pops a value off of the stack.

\f[B]z\f[] Pushes the current stack depth (before execution of this command).

These commands manipulate arrays.

\f[B]:\f[]\f[I]r\f[] Pops the top two values off of the stack. The second value will be stored in the array \f[I]r\f[] (see the \f[B]REGISTERS\f[] section), indexed by the first value.

\f[B];\f[]\f[I]r\f[] Pops the value on top of the stack and uses it as an index into the array \f[I]r\f[]. The selected value is then pushed onto the stack.

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 (\f[B]0\f[]) 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 (\f[B]\[aq]\\n\[aq]\f[]); it is a parse error for a newline to be used as a register name.

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 (\f[B]-x\f[] or \f[B]--extended-register\f[] command-line arguments are given), then normal single character registers are used \f[I]unless\f[] the character immediately following a command that needs a register name is a space (according to \f[B]isspace()\f[]) and not a newline (\f[B]\[aq]\\n\[aq]\f[]).

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

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 \f[B]EXIT STATUS\f[] section), it asks for more input; otherwise, it exits with the appropriate return code.

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

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

In addition, this dc(1) uses an even larger integer for overflow checking. This integer type depends on the value of \f[B]DC_LONG_BIT\f[], but is always at least twice as large as the integer type used to store digits.

The following are the limits on dc(1):

\f[B]DC_LONG_BIT\f[] The number of bits in the \f[B]long\f[] 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 \f[B]PERFORMANCE\f[] section).

\f[B]DC_BASE_DIGS\f[] The number of decimal digits per large integer (see the \f[B]PERFORMANCE\f[] section). Depends on \f[B]DC_LONG_BIT\f[].

\f[B]DC_BASE_POW\f[] The max decimal number that each large integer can store (see \f[B]DC_BASE_DIGS\f[]) plus \f[B]1\f[]. Depends on \f[B]DC_BASE_DIGS\f[].

\f[B]DC_OVERFLOW_MAX\f[] The max number that the overflow type (see the \f[B]PERFORMANCE\f[] section) can hold. Depends on \f[B]DC_LONG_BIT\f[].

\f[B]DC_BASE_MAX\f[] The maximum output base. Set at \f[B]DC_BASE_POW\f[].

\f[B]DC_DIM_MAX\f[] The maximum size of arrays. Set at \f[B]SIZE_MAX-1\f[].

\f[B]DC_SCALE_MAX\f[] The maximum \f[B]scale\f[]. Set at \f[B]DC_OVERFLOW_MAX-1\f[].

\f[B]DC_STRING_MAX\f[] The maximum length of strings. Set at \f[B]DC_OVERFLOW_MAX-1\f[].

\f[B]DC_NAME_MAX\f[] The maximum length of identifiers. Set at \f[B]DC_OVERFLOW_MAX-1\f[].

\f[B]DC_NUM_MAX\f[] The maximum length of a number (in decimal digits), which includes digits after the decimal point. Set at \f[B]DC_OVERFLOW_MAX-1\f[].

\f[B]DC_RAND_MAX\f[] The maximum integer (inclusive) returned by the \f[B]\[aq]\f[] command, if dc(1). Set at \f[B]2^DC_LONG_BIT-1\f[].

Exponent The maximum allowable exponent (positive or negative). Set at \f[B]DC_OVERFLOW_MAX\f[].

Number of vars The maximum number of vars/arrays. Set at \f[B]SIZE_MAX-1\f[].

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.

dc(1) recognizes the following environment variables:

\f[B]DC_ENV_ARGS\f[] 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 \f[B]DC_ENV_ARGS\f[] 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 \f[B]-e\f[] option to set \f[B]scale\f[] to a value other than \f[B]0\f[].

\f[B]DC_LINE_LENGTH\f[] If this environment variable exists and contains an integer that is greater than \f[B]1\f[] and is less than \f[B]UINT16_MAX\f[] (\f[B]2^16-1\f[]), dc(1) will output lines to that length, including the backslash newline combo. The default line length is \f[B]70\f[].

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

dc(1) returns the following exit statuses:

\f[B]0\f[] No error.

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

\f[B]2\f[] A parse error occurred.

\f[B]3\f[] A runtime error occurred.

\f[B]4\f[] A fatal error occurred.

The exit status \f[B]4\f[] is special; when a fatal error occurs, dc(1) always exits and returns \f[B]4\f[], 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 \f[B]INTERACTIVE MODE\f[] section), since dc(1) resets its state (see the \f[B]RESET\f[] 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 \f[B]-i\f[] flag or \f[B]--interactive\f[] 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 \f[B]-i\f[] flag or \f[B]--interactive\f[] option.

Like bc(1), dc(1) has an interactive mode and a non-interactive mode. Interactive mode is turned on automatically when both \f[B]stdin\f[] and \f[B]stdout\f[] are hooked to a terminal, but the \f[B]-i\f[] flag and \f[B]--interactive\f[] option can turn it on in other cases.

In interactive mode, dc(1) attempts to recover from errors (see the \f[B]RESET\f[] section), and in normal execution, flushes \f[B]stdout\f[] as soon as execution is done for the current input.

If \f[B]stdin\f[], \f[B]stdout\f[], and \f[B]stderr\f[] are all connected to a TTY, dc(1) turns on "TTY mode."

TTY mode is required for history to be enabled (see the \f[B]COMMAND LINE HISTORY\f[] section). It is also required to enable special handling for \f[B]SIGINT\f[] 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 \f[B]stdin\f[] and \f[B]stdout\f[] to be connected to a terminal.

Sending a \f[B]SIGINT\f[] will cause dc(1) to stop execution of the current input. If dc(1) is in TTY mode (see the \f[B]TTY MODE\f[] section), it will reset (see the \f[B]RESET\f[] 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 \f[B]stdin\f[] 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 \f[B]stdin\f[] if no other file exists.

This means that if a \f[B]SIGINT\f[] 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.

\f[B]SIGTERM\f[] and \f[B]SIGQUIT\f[] cause dc(1) to clean up and exit, and it uses the default handler for all other signals. The one exception is \f[B]SIGHUP\f[]; in that case, when dc(1) is in TTY mode, a \f[B]SIGHUP\f[] will cause dc(1) to clean up and exit.

dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see the \f[B]TTY MODE\f[] section), history is enabled. Previous lines can be recalled and edited with the arrow keys.

\f[B]Note\f[]: tabs are converted to 8 spaces.

This dc(1) ships with support for adding error messages for different locales and thus, supports \f[B]LC_MESSAGS\f[].

bc(1)

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.

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

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