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diff --git a/manuals/dc/EP.1.md b/manuals/dc/EP.1.md new file mode 100644 index 0000000000000..99bb462fb0a00 --- /dev/null +++ b/manuals/dc/EP.1.md @@ -0,0 +1,1025 @@ +<!--- + +SPDX-License-Identifier: BSD-2-Clause + +Copyright (c) 2018-2020 Gavin D. Howard and contributors. + +Redistribution and use in source and binary forms, with or without +modification, are permitted provided that the following conditions are met: + +* Redistributions of source code must retain the above copyright notice, this + list of conditions and the following disclaimer. + +* Redistributions in binary form must reproduce the above copyright notice, + this list of conditions and the following disclaimer in the documentation + and/or other materials provided with the distribution. + +THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" +AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE +LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR +CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF +SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS +INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN +CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) +ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +POSSIBILITY OF SUCH DAMAGE. + +--> + +# 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. + + In other dc(1) implementations, this option causes the program to execute + the expressions and then exit. This dc(1) does not, unless the + **DC_EXPR_EXIT** is defined (see the **ENVIRONMENT VARIABLES** section). + + 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. + + In other dc(1) implementations, this option causes the program to execute + the files and then exit. This dc(1) does not, unless the + **DC_EXPR_EXIT** is defined (see the **ENVIRONMENT VARIABLES** section). + + 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 <file> >&-**, 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 <file> 2>&-**, it will quit with an error. This +is done so that dc(1) can exit with an error code when **stderr** is redirected +to a file. + +If there are scripts that depend on the behavior of other dc(1) implementations, +it is recommended that those scripts be changed to redirect **stderr** to +**/dev/null**. + +# SYNTAX + +Each item in the input source code, either a number (see the **NUMBERS** +section) or a command (see the **COMMANDS** section), is processed and executed, +in order. Input is processed immediately when entered. + +**ibase** is a register (see the **REGISTERS** section) that determines how to +interpret constant numbers. It is the "input" base, or the number base used for +interpreting input numbers. **ibase** is initially **10**. The max allowable +value for **ibase** is **16**. The min allowable value for **ibase** is **2**. +The max allowable value for **ibase** can be queried in dc(1) programs with the +**T** command. + +**obase** is a register (see the **REGISTERS** section) that determines how to +output results. It is the "output" base, or the number base used for outputting +numbers. **obase** is initially **10**. The max allowable value for **obase** is +**DC_BASE_MAX** and can be queried with the **U** command. The min allowable +value for **obase** is **2**. Values are output in the specified base. + +The *scale* of an expression is the number of digits in the result of the +expression right of the decimal point, and **scale** is a register (see the +**REGISTERS** section) that sets the precision of any operations (with +exceptions). **scale** is initially **0**. **scale** cannot be negative. The max +allowable value for **scale** can be queried in dc(1) programs with the **V** +command. + +## Comments + +Comments go from **#** until, and not including, the next newline. This is a +**non-portable extension**. + +# NUMBERS + +Numbers are strings made up of digits, uppercase letters up to **F**, and at +most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits. +Uppercase letters are equal to **9** + their position in the alphabet (i.e., +**A** equals **10**, or **9+1**). If a digit or letter makes no sense with the +current value of **ibase**, they are set to the value of the highest valid digit +in **ibase**. + +Single-character numbers (i.e., **A** alone) take the value that they would have +if they were valid digits, regardless of the value of **ibase**. This means that +**A** alone always equals decimal **10** and **F** alone always equals decimal +**15**. + +# COMMANDS + +The valid commands are listed below. + +## Printing + +These commands are used for printing. + +**p** + +: Prints the value on top of the stack, whether number or string, and prints a + newline after. + + This does not alter the stack. + +**n** + +: Prints the value on top of the stack, whether number or string, and pops it + off of the stack. + +**P** + +: Pops a value off the stack. + + If the value is a number, it is truncated and the absolute value of the + result is printed as though **obase** is **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**. + +**G** + +: The top two values are popped off of the stack, they are compared, and a + **1** is pushed if they are equal, or **0** otherwise. + + This is a **non-portable extension**. + +**N** + +: The top value is popped off of the stack, and if it a **0**, a **1** is + pushed; otherwise, a **0** is pushed. + + This is a **non-portable extension**. + +**(** + +: The top two values are popped off of the stack, they are compared, and a + **1** is pushed if the first is less than the second, or **0** otherwise. + + This is a **non-portable extension**. + +**{** + +: The top two values are popped off of the stack, they are compared, and a + **1** is pushed if the first is less than or equal to the second, or **0** + otherwise. + + This is a **non-portable extension**. + +**)** + +: The top two values are popped off of the stack, they are compared, and a + **1** is pushed if the first is greater than the second, or **0** otherwise. + + This is a **non-portable extension**. + +**}** + +: The top two values are popped off of the stack, they are compared, and a + **1** is pushed if the first is greater than or equal to the second, or + **0** otherwise. + + This is a **non-portable extension**. + +**M** + +: The top two values are popped off of the stack. If they are both non-zero, a + **1** is pushed onto the stack. If either of them is zero, or both of them + are, then a **0** is pushed onto the stack. + + This is like the **&&** operator in bc(1), and it is *not* a short-circuit + operator. + + This is a **non-portable extension**. + +**m** + +: The top two values are popped off of the stack. If at least one of them is + non-zero, a **1** is pushed onto the stack. If both of them are zero, then a + **0** is pushed onto the stack. + + This is like the **||** operator in bc(1), and it is *not* a short-circuit + operator. + + This is a **non-portable extension**. + +## Stack Control + +These commands control the stack. + +**c** + +: Removes all items from ("clears") the stack. + +**d** + +: Copies the item on top of the stack ("duplicates") and pushes the copy onto + the stack. + +**r** + +: Swaps ("reverses") the two top items on the stack. + +**R** + +: Pops ("removes") the top value from the stack. + +## Register Control + +These commands control registers (see the **REGISTERS** section). + +**s***r* + +: Pops the value off the top of the stack and stores it into register *r*. + +**l***r* + +: Copies the value in register *r* and pushes it onto the stack. This does not + alter the contents of *r*. + +**S***r* + +: 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. + +**L***r* + +: 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 **l***r* command. + +## Parameters + +These commands control the values of **ibase**, **obase**, and **scale**. Also +see the **SYNTAX** section. + +**i** + +: Pops the value off of the top of the stack and uses it to set **ibase**, + which must be between **2** and **16**, inclusive. + + If the value on top of the stack has any *scale*, the *scale* is ignored. + +**o** + +: Pops the value off of the top of the stack and uses it to set **obase**, + which must be between **2** and **DC_BASE_MAX**, inclusive (see the + **LIMITS** section). + + If the value on top of the stack has any *scale*, the *scale* is ignored. + +**k** + +: Pops the value off of the top of the stack and uses it to set **scale**, + which must be non-negative. + + If the value on top of the stack has any *scale*, the *scale* is ignored. + +**I** + +: Pushes the current value of **ibase** onto the main stack. + +**O** + +: Pushes the current value of **obase** onto the main stack. + +**K** + +: Pushes the current value of **scale** onto the main stack. + +**T** + +: Pushes the maximum allowable value of **ibase** onto the main stack. + + This is a **non-portable extension**. + +**U** + +: Pushes the maximum allowable value of **obase** onto the main stack. + + This is a **non-portable extension**. + +**V** + +: Pushes the maximum allowable value of **scale** onto the main stack. + + This is a **non-portable extension**. + +## Strings + +The following commands control strings. + +dc(1) can work with both numbers and strings, and registers (see the +**REGISTERS** section) can hold both strings and numbers. dc(1) always knows +whether the contents of a register are a string or a number. + +While arithmetic operations have to have numbers, and will print an error if +given a string, other commands accept strings. + +Strings can also be executed as macros. For example, if the string **[1pR]** is +executed as a macro, then the code **1pR** is executed, meaning that the **1** +will be printed with a newline after and then popped from the stack. + +**\[**_characters_**\]** + +: Makes a string containing *characters* and pushes it onto the stack. + + If there are brackets (**\[** and **\]**) in the string, then they must be + balanced. Unbalanced brackets can be escaped using a backslash (**\\**) + character. + + If there is a backslash character in the string, the character after it + (even another backslash) is put into the string verbatim, but the (first) + backslash is not. + +**a** + +: The value on top of the stack is popped. + + If it is a number, it is truncated and its absolute value is taken. The + result mod **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). + +**>***r***e***s* + +: 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). + +**!\>***r***e***s* + +: 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). + +**\<***r***e***s* + +: 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). + +**!\<***r***e***s* + +: 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). + +**=***r***e***s* + +: 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). + +**!=***r***e***s* + +: 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**. + +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, attempting to convert a negative number to a hardware integer, + overflow when converting a number to a hardware integer, and attempting to + use a non-integer where an integer is required. + + Converting to a hardware integer happens for the second operand of the power + (**\^**) operator. + +**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 required for history to be enabled (see the **COMMAND LINE HISTORY** +section). It is also required to enable special handling for **SIGINT** signals. + +TTY mode is different from interactive mode because interactive mode is required +in the [bc(1) specification][1], 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. The one exception is **SIGHUP**; in that +case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and +exit. + +# COMMAND LINE HISTORY + +dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see +the **TTY MODE** section), history is enabled. Previous lines can be recalled +and edited with the arrow keys. + +**Note**: tabs are converted to 8 spaces. + +# LOCALES + +This dc(1) ships with support for adding error messages for different locales +and thus, supports **LC_MESSAGS**. + +# 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”)][1] specification. + +# BUGS + +None are known. Report bugs at https://git.yzena.com/gavin/bc. + +# AUTHOR + +Gavin D. Howard <yzena.tech@gmail.com> and contributors. + +[1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html |