dc - arbitrary-precision decimal reverse-Polish notation calculator

\f[B]dc\f[R] [\f[B]-cChiPRvVx\f[R]] [\f[B]--version\f[R]] [\f[B]--help\f[R]] [\f[B]--digit-clamp\f[R]] [\f[B]--no-digit-clamp\f[R]] [\f[B]--interactive\f[R]] [\f[B]--no-prompt\f[R]] [\f[B]--no-read-prompt\f[R]] [\f[B]--extended-register\f[R]] [\f[B]-e\f[R] \f[I]expr\f[R]] [\f[B]--expression\f[R]=\f[I]expr\f[R]...] [\f[B]-f\f[R] \f[I]file\f[R]...] [\f[B]--file\f[R]=\f[I]file\f[R]...] [\f[I]file\f[R]...]

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 \f[B]stdin\f[R] (see the \f[B]STDIN\f[R] 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 \f[B]DC_ENV_ARGS\f[R] (see the \f[B]ENVIRONMENT VARIABLES\f[R] section). For example, if a user wants the \f[B]scale\f[R] always set to \f[B]10\f[R], they can set \f[B]DC_ENV_ARGS\f[R] to \f[B]-e 10k\f[R], and this dc(1) will always start with a \f[B]scale\f[R] of \f[B]10\f[R].

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

\f[B]-C\f[R], \f[B]--no-digit-clamp\f[R] Disables clamping of digits greater than or equal to the current \f[B]ibase\f[R] when parsing numbers.

\f[B]-c\f[R], \f[B]--digit-clamp\f[R] Enables clamping of digits greater than or equal to the current \f[B]ibase\f[R] when parsing numbers.

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

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

\f[B]-I\f[R] \f[I]ibase\f[R], \f[B]--ibase\f[R]=\f[I]ibase\f[R] Sets the builtin variable \f[B]ibase\f[R] to the value \f[I]ibase\f[R] assuming that \f[I]ibase\f[R] is in base 10. It is a fatal error if \f[I]ibase\f[R] is not a valid number.

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

\f[B]-L\f[R], \f[B]--no-line-length\f[R] Disables line length checking and prints numbers without backslashes and newlines. In other words, this option sets \f[B]BC_LINE_LENGTH\f[R] to \f[B]0\f[R] (see the \f[B]ENVIRONMENT VARIABLES\f[R] section).

\f[B]-O\f[R] \f[I]obase\f[R], \f[B]--obase\f[R]=\f[I]obase\f[R] Sets the builtin variable \f[B]obase\f[R] to the value \f[I]obase\f[R] assuming that \f[I]obase\f[R] is in base 10. It is a fatal error if \f[I]obase\f[R] is not a valid number.

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

\f[B]-R\f[R], \f[B]--no-read-prompt\f[R] Disables the read prompt in TTY mode. (The read prompt is only enabled in TTY mode. See the \f[B]TTY MODE\f[R] 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 \f[B]BC_ENV_ARGS\f[R] (see the \f[B]ENVIRONMENT VARIABLES\f[R] section). This option is also useful in hash bang lines of dc(1) scripts that prompt for user input.

\f[B]-S\f[R] \f[I]scale\f[R], \f[B]--scale\f[R]=\f[I]scale\f[R] Sets the builtin variable \f[B]scale\f[R] to the value \f[I]scale\f[R] assuming that \f[I]scale\f[R] is in base 10. It is a fatal error if \f[I]scale\f[R] is not a valid number.

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

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

\f[B]-z\f[R], \f[B]--leading-zeroes\f[R] Makes dc(1) print all numbers greater than \f[B]-1\f[R] and less than \f[B]1\f[R], and not equal to \f[B]0\f[R], with a leading zero.

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

If no files are given on the command-line and no files or expressions are given by the \f[B]-f\f[R], \f[B]--file\f[R], \f[B]-e\f[R], or \f[B]--expression\f[R] options, then dc(1) reads from \f[B]stdin\f[R].

However, there is a caveat to this.

First, \f[B]stdin\f[R] 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.

Any non-error output is written to \f[B]stdout\f[R]. In addition, if history (see the \f[B]HISTORY\f[R] section) and the prompt (see the \f[B]TTY MODE\f[R] section) are enabled, both are output to \f[B]stdout\f[R].

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

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

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

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

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

\f[B]obase\f[R] is a register (see the \f[B]REGISTERS\f[R] section) that determines how to output results. It is the \[lq]output\[rq] base, or the number base used for outputting numbers. \f[B]obase\f[R] is initially \f[B]10\f[R]. The max allowable value for \f[B]obase\f[R] is \f[B]DC_BASE_MAX\f[R] and can be queried with the \f[B]U\f[R] command. The min allowable value for \f[B]obase\f[R] is \f[B]2\f[R]. Values are output in the specified base.

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

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

Numbers are strings made up of digits, uppercase letters up to \f[B]F\f[R], and at most \f[B]1\f[R] period for a radix. Numbers can have up to \f[B]DC_NUM_MAX\f[R] digits. Uppercase letters are equal to \f[B]9\f[R] plus their position in the alphabet (i.e., \f[B]A\f[R] equals \f[B]10\f[R], or \f[B]9+1\f[R]).

If a digit or letter makes no sense with the current value of \f[B]ibase\f[R] (i.e., they are greater than or equal to the current value of \f[B]ibase\f[R]), then the behavior depends on the existence of the \f[B]-c\f[R]/\f[B]--digit-clamp\f[R] or \f[B]-C\f[R]/\f[B]--no-digit-clamp\f[R] options (see the \f[B]OPTIONS\f[R] section), the existence and setting of the \f[B]DC_DIGIT_CLAMP\f[R] environment variable (see the \f[B]ENVIRONMENT VARIABLES\f[R] section), or the default, which can be queried with the \f[B]-h\f[R]/\f[B]--help\f[R] option.

If clamping is off, then digits or letters that are greater than or equal to the current value of \f[B]ibase\f[R] are not changed. Instead, their given value is multiplied by the appropriate power of \f[B]ibase\f[R] and added into the number. This means that, with an \f[B]ibase\f[R] of \f[B]3\f[R], the number \f[B]AB\f[R] is equal to \f[B]3\[ha]1*A+3\[ha]0*B\f[R], which is \f[B]3\f[R] times \f[B]10\f[R] plus \f[B]11\f[R], or \f[B]41\f[R].

If clamping is on, then digits or letters that are greater than or equal to the current value of \f[B]ibase\f[R] are set to the value of the highest valid digit in \f[B]ibase\f[R] before being multiplied by the appropriate power of \f[B]ibase\f[R] and added into the number. This means that, with an \f[B]ibase\f[R] of \f[B]3\f[R], the number \f[B]AB\f[R] is equal to \f[B]3\[ha]1*2+3\[ha]0*2\f[R], which is \f[B]3\f[R] times \f[B]2\f[R] plus \f[B]2\f[R], or \f[B]8\f[R].

There is one exception to clamping: single-character numbers (i.e., \f[B]A\f[R] alone). Such numbers are never clamped and always take the value they would have in the highest possible \f[B]ibase\f[R]. This means that \f[B]A\f[R] alone always equals decimal \f[B]10\f[R] and \f[B]Z\f[R] alone always equals decimal \f[B]35\f[R]. This behavior is mandated by the standard for bc(1) (see the STANDARDS section) and is meant to provide an easy way to set the current \f[B]ibase\f[R] (with the \f[B]i\f[R] command) regardless of the current value of \f[B]ibase\f[R].

If clamping is on, and the clamped value of a character is needed, use a leading zero, i.e., for \f[B]A\f[R], use \f[B]0A\f[R].

The valid commands are listed below.

These commands are used for printing.

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

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

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

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

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

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

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

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

\f[B]\[ti]\f[R] 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[R] except that \f[B]x\f[R] and \f[B]y\f[R] are only evaluated once.

\f[B]\[ha]\f[R] 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 \f[I]scale\f[R] of the result is equal to \f[B]scale\f[R].

\f[B]v\f[R] 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[R] of the result is equal to \f[B]scale\f[R].

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

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

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

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

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

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

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

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

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

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

These commands control the stack.

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

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

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

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

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

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

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

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

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

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

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

\f[B]o\f[R] Pops the value off of the top of the stack and uses it to set \f[B]obase\f[R], which must be between \f[B]2\f[R] and \f[B]DC_BASE_MAX\f[R], inclusive (see the \f[B]LIMITS\f[R] section).

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

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

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

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

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

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

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

The following commands control strings.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

\f[B]q\f[R] 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[R] 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.

\f[B],\f[R] 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 \f[B]Q\f[R] command, so the sequence \f[B],Q\f[R] will make dc(1) exit.

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

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

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

\f[B]u\f[R] Pops one value off of the stack. If the value is a number, this pushes \f[B]1\f[R] onto the stack. Otherwise (if it is a string), it pushes \f[B]0\f[R].

\f[B]t\f[R] Pops one value off of the stack. If the value is a string, this pushes \f[B]1\f[R] onto the stack. Otherwise (if it is a number), it pushes \f[B]0\f[R].

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

\f[B]y\f[R]\f[I]r\f[R] Pushes the current stack depth of the register \f[I]r\f[R] onto the main stack.

These commands manipulate arrays.

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

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

\f[B]Y\f[R]\f[I]r\f[R] Pushes the length of the array \f[I]r\f[R] onto the stack.

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

\f[B]gl\f[R] Pushes the line length set by \f[B]DC_LINE_LENGTH\f[R] (see the \f[B]ENVIRONMENT VARIABLES\f[R] section) onto the stack.

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

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[R]) 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 (\f[B]`\[rs]n'\f[R]) and a left bracket (\f[B]`['\f[R]); it is a parse error for a newline or a left bracket 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[R] or \f[B]--extended-register\f[R] command-line arguments are given), then normal single character registers are used \f[I]unless\f[R] the character immediately following a command that needs a register name is a space (according to \f[B]isspace()\f[R]) and not a newline (\f[B]`\[rs]n'\f[R]).

In that case, the register name is found according to the regex \f[B][a-z][a-z0-9_]*\f[R] (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[R] section), it asks for more input; otherwise, it exits with the appropriate return code.

Most dc(1) implementations use \f[B]char\f[R] types to calculate the value of \f[B]1\f[R] 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[R] decimal digit at a time. If built in a environment where \f[B]DC_LONG_BIT\f[R] (see the \f[B]LIMITS\f[R] section) is \f[B]64\f[R], then each integer has \f[B]9\f[R] decimal digits. If built in an environment where \f[B]DC_LONG_BIT\f[R] is \f[B]32\f[R] then each integer has \f[B]4\f[R] decimal digits. This value (the number of decimal digits per large integer) is called \f[B]DC_BASE_DIGS\f[R].

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[R], 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[R] The number of bits in the \f[B]long\f[R] 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[R] section).

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

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

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

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

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

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

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

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

\f[B]DC_NUM_MAX\f[R] 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[R].

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

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

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.

As \f[B]non-portable extensions\f[R], dc(1) recognizes the following environment variables:

\f[B]DC_ENV_ARGS\f[R] 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[R] will be processed before arguments and files given on the command-line. This gives the user the ability to set up \[lq]standard\[rq] 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[R] option to set \f[B]scale\f[R] to a value other than \f[B]0\f[R].

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

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

\f[B]DC_TTY_MODE\f[R] If TTY mode is \f[I]not\f[R] available (see the \f[B]TTY MODE\f[R] section), then this environment variable has no effect.

\f[B]DC_PROMPT\f[R] If TTY mode is \f[I]not\f[R] available (see the \f[B]TTY MODE\f[R] section), then this environment variable has no effect.

\f[B]DC_EXPR_EXIT\f[R] If any expressions or expression files are given on the command-line with \f[B]-e\f[R], \f[B]--expression\f[R], \f[B]-f\f[R], or \f[B]--file\f[R], then if this environment variable exists and contains an integer, a non-zero value makes dc(1) exit after executing the expressions and expression files, and a zero value makes dc(1) not exit.

\f[B]DC_DIGIT_CLAMP\f[R] When parsing numbers and if this environment variable exists and contains an integer, a non-zero value makes dc(1) clamp digits that are greater than or equal to the current \f[B]ibase\f[R] so that all such digits are considered equal to the \f[B]ibase\f[R] minus 1, and a zero value disables such clamping so that those digits are always equal to their value, which is multiplied by the power of the \f[B]ibase\f[R].

dc(1) returns the following exit statuses:

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

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

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

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

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

The exit status \f[B]4\f[R] is special; when a fatal error occurs, dc(1) always exits and returns \f[B]4\f[R], 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[R] section), since dc(1) resets its state (see the \f[B]RESET\f[R] 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[R] flag or \f[B]--interactive\f[R] 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[R] flag or \f[B]--interactive\f[R] 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[R] and \f[B]stdout\f[R] are hooked to a terminal, but the \f[B]-i\f[R] flag and \f[B]--interactive\f[R] option can turn it on in other situations.

In interactive mode, dc(1) attempts to recover from errors (see the \f[B]RESET\f[R] section), and in normal execution, flushes \f[B]stdout\f[R] as soon as execution is done for the current input. dc(1) may also reset on \f[B]SIGINT\f[R] instead of exit, depending on the contents of, or default for, the \f[B]DC_SIGINT_RESET\f[R] environment variable (see the \f[B]ENVIRONMENT VARIABLES\f[R] section).

If \f[B]stdin\f[R], \f[B]stdout\f[R], and \f[B]stderr\f[R] are all connected to a TTY, then \[lq]TTY mode\[rq] is considered to be available, and thus, dc(1) can turn on TTY mode, subject to some settings.

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

If the environment variable \f[B]DC_TTY_MODE\f[R] does \f[I]not\f[R] exist, the default setting is used. The default setting can be queried with the \f[B]-h\f[R] or \f[B]--help\f[R] options.

TTY mode is different from interactive mode because interactive mode is required in the bc(1) specification (see the \f[B]STANDARDS\f[R] section), and interactive mode requires only \f[B]stdin\f[R] and \f[B]stdout\f[R] to be connected to a terminal.

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: \f[B]DC_PROMPT\f[R] (see the \f[B]ENVIRONMENT VARIABLES\f[R] section).

If the environment variable \f[B]DC_PROMPT\f[R] exists and is a non-zero integer, then the prompt is turned on when \f[B]stdin\f[R], \f[B]stdout\f[R], and \f[B]stderr\f[R] are connected to a TTY and the \f[B]-P\f[R] and \f[B]--no-prompt\f[R] options were not used. The read prompt will be turned on under the same conditions, except that the \f[B]-R\f[R] and \f[B]--no-read-prompt\f[R] options must also not be used.

However, if \f[B]DC_PROMPT\f[R] does not exist, the prompt can be enabled or disabled with the \f[B]DC_TTY_MODE\f[R] environment variable, the \f[B]-P\f[R] and \f[B]--no-prompt\f[R] options, and the \f[B]-R\f[R] and \f[B]--no-read-prompt\f[R] options. See the \f[B]ENVIRONMENT VARIABLES\f[R] and \f[B]OPTIONS\f[R] sections for more details.

Sending a \f[B]SIGINT\f[R] will cause dc(1) to do one of two things.

If dc(1) is not in interactive mode (see the \f[B]INTERACTIVE MODE\f[R] section), or the \f[B]DC_SIGINT_RESET\f[R] environment variable (see the \f[B]ENVIRONMENT VARIABLES\f[R] 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 \f[B]DC_SIGINT_RESET\f[R] or its default is an integer and non-zero, then dc(1) will stop executing the current input and reset (see the \f[B]RESET\f[R] section) upon receiving a \f[B]SIGINT\f[R].

Note that \[lq]current input\[rq] can mean one of two things. If dc(1) is processing input from \f[B]stdin\f[R] 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 \f[B]stdin\f[R] if no other file exists.

This means that if a \f[B]SIGINT\f[R] 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[R] and \f[B]SIGQUIT\f[R] cause dc(1) to clean up and exit, and it uses the default handler for all other signals.

bc(1)

The dc(1) utility operators and some behavior are compliant with the operators in the IEEE Std 1003.1-2017 (\[lq]POSIX.1-2017\[rq]) bc(1) specification at https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html .

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

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