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DC(1) General Commands Manual DC(1)

Name
dc - arbitrary-precision decimal reverse-Polish notation calculator

SYNOPSIS
dc [-cChiPRvVx] [--version] [--help] [--digit-clamp] [--no-digit-clamp]
[--interactive] [--no-prompt] [--no-read-prompt] [--extended-register]
[-e expr] [--expression=expr...] [-f file...] [--file=file...]
[file...] [-I ibase] [--ibase=ibase] [-O obase] [--obase=obase] [-S
scale] [--scale=scale] [-E seed] [--seed=seed]

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

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

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

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

-C, --no-digit-clamp
Disables clamping of digits greater than or equal to the current
ibase when parsing numbers.

This means that the value added to a number from a digit is
always that digit's value multiplied by the value of ibase
raised to the power of the digit's position, which starts from 0
at the least significant digit.

If this and/or the -c or --digit-clamp options are given
multiple times, the last one given is used.

This option overrides the DC_DIGIT_CLAMP environment variable
(see the ENVIRONMENT VARIABLES section) and the default, which
can be queried with the -h or --help options.

This is a non-portable extension.

-c, --digit-clamp
Enables clamping of digits greater than or equal to the current
ibase when parsing numbers.

This means that digits that the value added to a number from a
digit that is greater than or equal to the ibase is the value of
ibase minus 1 all multiplied by the value of ibase raised to the
power of the digit's position, which starts from 0 at the least
significant digit.

If this and/or the -C or --no-digit-clamp options are given
multiple times, the last one given is used.

This option overrides the DC_DIGIT_CLAMP environment variable
(see the ENVIRONMENT VARIABLES section) and the default, which
can be queried with the -h or --help options.

This is a non-portable extension.

-E seed, --seed=seed
Sets the builtin variable seed to the value seed assuming that
seed is in base 10. It is a fatal error if seed is not a valid
number.

If multiple instances of this option are given, the last is
used.

This is a non-portable extension.

-e expr, --expression=expr
Evaluates expr. If multiple expressions are given, they are
evaluated in order. If files are given as well (see below), the
expressions and files are evaluated in the order given. This
means that if a file is given before an expression, the file is
read in and evaluated first.

If this option is given on the command-line (i.e., not in
DC_ENV_ARGS, see the ENVIRONMENT VARIABLES section), then after
processing all expressions and files, dc(1) will exit, unless -
(stdin) was given as an argument at least once to -f or --file,
whether on the command-line or in DC_ENV_ARGS. However, if any
other -e, --expression, -f, or --file arguments are given after
-f- or equivalent is given, dc(1) will give a fatal error and
exit.

This is a non-portable extension.

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

If this option is given on the command-line (i.e., not in
DC_ENV_ARGS, see the ENVIRONMENT VARIABLES section), then after
processing all expressions and files, dc(1) will exit, unless -
(stdin) was given as an argument at least once to -f or --file.
However, if any other -e, --expression, -f, or --file arguments
are given after -f- or equivalent is given, dc(1) will give a
fatal error and exit.

This is a non-portable extension.

-h, --help
Prints a usage message and exits.

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

If multiple instances of this option are given, the last is
used.

This is a non-portable extension.

-i, --interactive
Forces interactive mode. (See the INTERACTIVE MODE section.)

This is a non-portable extension.

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

This is a non-portable extension.

-O obase, --obase=obase
Sets the builtin variable obase to the value obase assuming that
obase is in base 10. It is a fatal error if obase is not a
valid number.

If multiple instances of this option are given, the last is
used.

This is a non-portable extension.

-P, --no-prompt
Disables the prompt in TTY mode. (The prompt is only enabled in
TTY mode. See the TTY MODE section.) This is mostly for those
users that do not want a prompt or are not used to having them
in dc(1). Most of those users would want to put this option in
DC_ENV_ARGS.

These options override the DC_PROMPT and DC_TTY_MODE environment
variables (see the ENVIRONMENT VARIABLES section).

This is a non-portable extension.

-R, --no-read-prompt
Disables the read prompt in TTY mode. (The read prompt is only
enabled in TTY mode. See the TTY MODE section.) This is mostly
for those users that do not want a read prompt or are not used
to having them in dc(1). Most of those users would want to put
this option in BC_ENV_ARGS (see the ENVIRONMENT VARIABLES
section). This option is also useful in hash bang lines of
dc(1) scripts that prompt for user input.

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

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

This is a non-portable extension.

-S scale, --scale=scale
Sets the builtin variable scale to the value scale assuming that
scale is in base 10. It is a fatal error if scale is not a
valid number.

If multiple instances of this option are given, the last is
used.

This is a non-portable extension.

-v, -V, --version
Print the version information (copyright header) and exits.

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

This is a non-portable extension.

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

This is a non-portable extension.

All long options are non-portable extensions.

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

However, there is a caveat to this.

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

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

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

If there are scripts that depend on the behavior of other dc(1)
implementations, it is recommended that those scripts be changed to
redirect stdout to /dev/null.

STDERR
Any error output is written to stderr.

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

If there are scripts that depend on the behavior of other dc(1)
implementations, it is recommended that those scripts be changed to
redirect stderr to /dev/null.

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

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

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

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

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

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

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

Note: The values returned by the pseudo-random number generator with
the ' and " commands are guaranteed to NOT be cryptographically secure.
This is a consequence of using a seeded pseudo-random number generator.
However, they are guaranteed to be reproducible with identical seed
values. This means that the pseudo-random values from dc(1) should
only be used where a reproducible stream of pseudo-random numbers is
ESSENTIAL. In any other case, use a non-seeded pseudo-random number
generator.

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

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

NUMBERS
Numbers are strings made up of digits, uppercase letters up to F, and
at most 1 period for a radix. Numbers can have up to DC_NUM_MAX
digits. Uppercase letters are equal to 9 plus 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
(i.e., they are greater than or equal to the current value of ibase),
then the behavior depends on the existence of the -c/--digit-clamp or
-C/--no-digit-clamp options (see the OPTIONS section), the existence
and setting of the DC_DIGIT_CLAMP environment variable (see the
ENVIRONMENT VARIABLES section), or the default, which can be queried
with the -h/--help option.

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

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

There is one exception to clamping: single-character numbers (i.e., A
alone). Such numbers are never clamped and always take the value they
would have in the highest possible ibase. This means that A alone
always equals decimal 10 and Z alone always equals decimal 35. 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 ibase
(with the i command) regardless of the current value of ibase.

If clamping is on, and the clamped value of a character is needed, use
a leading zero, i.e., for A, use 0A.

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

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

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

COMMANDS
The valid commands are listed below.

Printing
These commands are used for printing.

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

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

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

This does not alter the stack.

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

P Pops a value off the stack.

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

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

This is a non-portable extension.

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

Users should use this command when they get lost.

Arithmetic
These are the commands used for arithmetic.

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

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

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

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

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

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

Remaindering is equivalent to 1) Computing a/b to current scale,
and 2) Using the result of step 1 to calculate a-(a/b)*b to
scale max(scale+scale(b),scale(a)).

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

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

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

This is a non-portable extension.

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

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

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

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

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

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

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

This is a non-portable extension.

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

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

This is a non-portable extension.

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

This is a non-portable extension.

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

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

This is a non-portable extension.

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

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

This is a non-portable extension.

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

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

This is a non-portable extension.

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

This is a non-portable extension.

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

This is a non-portable extension.

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

This is a non-portable extension.

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

This is a non-portable extension.

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

This is a non-portable extension.

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

This is a non-portable extension.

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

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

This is a non-portable extension.

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

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

This is a non-portable extension.

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

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

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

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

This is a non-portable extension.

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

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

This is a non-portable extension.

Stack Control
These commands control the stack.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The scale and sign of the value may be significant.

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

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

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

This is a non-portable extension.

I Pushes the current value of ibase onto the main stack.

O Pushes the current value of obase onto the main stack.

K Pushes the current value of scale onto the main stack.

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

This is a non-portable extension.

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

This is a non-portable extension.

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

This is a non-portable extension.

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

This is a non-portable extension.

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

This is a non-portable extension.

Strings
The following commands control strings.

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

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

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

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

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

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

a The value on top of the stack is popped.

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

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

This is a non-portable extension.

x Pops a value off of the top of the stack.

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

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

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

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

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

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

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

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

This is a non-portable extension.

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

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

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

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

This is a non-portable extension.

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

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

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

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

This is a non-portable extension.

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

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

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

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

This is a non-portable extension.

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

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

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

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

This is a non-portable extension.

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

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

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

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

This is a non-portable extension.

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

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

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

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

This is a non-portable extension.

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

Z Pops a value off of the stack.

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

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

X Pops a value off of the stack.

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

If it is a string, pushes 0.

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

This is a non-portable extension.

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

This is a non-portable extension.

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

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

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

This is a non-portable extension.

Arrays
These commands manipulate arrays.

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

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

Yr Pushes the length of the array r onto the stack.

This is a non-portable extension.

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

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

gx Pushes 1 onto the stack if extended register mode is on, 0
otherwise. See the Extended Register Mode subsection of the
REGISTERS section for more information.

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

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

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

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

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

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

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

RESET
When dc(1) encounters an error or a signal that it has a non-default
handler for, it resets. This means that several things happen.

First, any macros that are executing are stopped and popped off the
stack. The behavior is not unlike that of exceptions in programming
languages. Then the execution point is set so that any code waiting to
execute (after all macros returned) is skipped.

Thus, when dc(1) resets, it skips any remaining code waiting to be
executed. Then, if it is interactive mode, and the error was not a
fatal error (see the EXIT STATUS section), it asks for more input;
otherwise, it exits with the appropriate return code.

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

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

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

LIMITS
The following are the limits on dc(1):

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

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

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

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

DC_BASE_MAX
The maximum output base. Set at DC_BASE_POW.

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

DC_SCALE_MAX
The maximum scale. Set at DC_OVERFLOW_MAX-1.

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

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

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

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

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

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

These limits are meant to be effectively non-existent; the limits are
so large (at least on 64-bit machines) that there should not be any
point at which they become a problem. In fact, memory should be
exhausted before these limits should be hit.

ENVIRONMENT VARIABLES
As non-portable extensions, dc(1) recognizes the following environment
variables:

DC_ENV_ARGS
This is another way to give command-line arguments to dc(1).
They should be in the same format as all other command-line
arguments. These are always processed first, so any files given
in DC_ENV_ARGS will be processed before arguments and files
given on the command-line. This gives the user the ability to
set up "standard" options and files to be used at every
invocation. The most useful thing for such files to contain
would be useful functions that the user might want every time
dc(1) runs. Another use would be to use the -e option to set
scale to a value other than 0.

The code that parses DC_ENV_ARGS will correctly handle quoted
arguments, but it does not understand escape sequences. For
example, the string "/home/gavin/some dc file.dc" will be
correctly parsed, but the string "/home/gavin/some "dc" file.dc"
will include the backslashes.

The quote parsing will handle either kind of quotes, ' or ".
Thus, if you have a file with any number of single quotes in the
name, you can use double quotes as the outside quotes, as in
"some `dc' file.dc", and vice versa if you have a file with
double quotes. However, handling a file with both kinds of
quotes in DC_ENV_ARGS is not supported due to the complexity of
the parsing, though such files are still supported on the
command-line where the parsing is done by the shell.

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

The special value of 0 will disable line length checking and
print numbers without regard to line length and without
backslashes and newlines.

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

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

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

DC_TTY_MODE
If TTY mode is not available (see the TTY MODE section), then
this environment variable has no effect.

However, when TTY mode is available, then if this environment
variable exists and contains an integer, then a non-zero value
makes dc(1) use TTY mode, and zero makes dc(1) not use TTY mode.

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

DC_PROMPT
If TTY mode is not available (see the TTY MODE section), then
this environment variable has no effect.

However, when TTY mode is available, then if this environment
variable exists and contains an integer, a non-zero value makes
dc(1) use a prompt, and zero or a non-integer makes dc(1) not
use a prompt. If this environment variable does not exist and
DC_TTY_MODE does, then the value of the DC_TTY_MODE environment
variable is used.

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

DC_EXPR_EXIT
If any expressions or expression files are given on the command-
line with -e, --expression, -f, or --file, 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.

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

DC_DIGIT_CLAMP
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 ibase so that all
such digits are considered equal to the ibase 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 ibase.

This never applies to single-digit numbers, as per the bc(1)
standard (see the STANDARDS section).

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

EXIT STATUS
dc(1) returns the following exit statuses:

0 No error.

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

Math errors include divide by 0, taking the square root of a
negative number, using a negative number as a bound for the
pseudo-random number generator, attempting to convert a negative
number to a hardware integer, overflow when converting a number
to a hardware integer, overflow when calculating the size of a
number, and attempting to use a non-integer where an integer is
required.

Converting to a hardware integer happens for the second operand
of the power (^), places (@), left shift (H), and right shift
(h) operators.

2 A parse error occurred.

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

3 A runtime error occurred.

Runtime errors include assigning an invalid number to any global
(ibase, obase, or scale), giving a bad expression to a read()
call, calling read() inside of a read() call, type errors
(including attempting to execute a number), and attempting an
operation when the stack has too few elements.

4 A fatal error occurred.

Fatal errors include memory allocation errors, I/O errors,
failing to open files, attempting to use files that do not have
only ASCII characters (dc(1) only accepts ASCII characters),
attempting to open a directory as a file, and giving invalid
command-line options.

The exit status 4 is special; when a fatal error occurs, dc(1) always
exits and returns 4, no matter what mode dc(1) is in.

The other statuses will only be returned when dc(1) is not in
interactive mode (see the INTERACTIVE MODE section), since dc(1) resets
its state (see the RESET section) and accepts more input when one of
those errors occurs in interactive mode. This is also the case when
interactive mode is forced by the -i flag or --interactive option.

These exit statuses allow dc(1) to be used in shell scripting with
error checking, and its normal behavior can be forced by using the -i
flag or --interactive option.

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

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

TTY MODE
If stdin, stdout, and stderr are all connected to a TTY, then "TTY
mode" is considered to be available, and thus, dc(1) can turn on TTY
mode, subject to some settings.

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

If the environment variable DC_TTY_MODE does not exist, the default
setting is used. The default setting can be queried with the -h or
--help options.

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

Command-Line History
Command-line history is only enabled if TTY mode is, i.e., that stdin,
stdout, and stderr are connected to a TTY and the DC_TTY_MODE
environment variable (see the ENVIRONMENT VARIABLES section) and its
default do not disable TTY mode. See the COMMAND LINE HISTORY section
for more information.

Prompt
If TTY mode is available, then a prompt can be enabled. Like TTY mode
itself, it can be turned on or off with an environment variable:
DC_PROMPT (see the ENVIRONMENT VARIABLES section).

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

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

SIGNAL HANDLING
Sending a SIGINT will cause dc(1) to do one of two things.

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

However, if dc(1) is in interactive mode, and the DC_SIGINT_RESET or
its default is an integer and non-zero, then dc(1) will stop executing
the current input and reset (see the RESET section) upon receiving a
SIGINT.

Note that "current input" can mean one of two things. If dc(1) is
processing input from stdin in interactive mode, it will ask for more
input. If dc(1) is processing input from a file in interactive mode,
it will stop processing the file and start processing the next file, if
one exists, or ask for input from stdin if no other file exists.

This means that if a SIGINT is sent to dc(1) as it is executing a file,
it can seem as though dc(1) did not respond to the signal since it will
immediately start executing the next file. This is by design; most
files that users execute when interacting with dc(1) have function
definitions, which are quick to parse. If a file takes a long time to
execute, there may be a bug in that file. The rest of the files could
still be executed without problem, allowing the user to continue.

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

COMMAND LINE HISTORY
dc(1) supports interactive command-line editing.

If dc(1) can be in TTY mode (see the TTY MODE section), history can be
enabled. This means that command-line history can only be enabled when
stdin, stdout, and stderr are all connected to a TTY.

Like TTY mode itself, it can be turned on or off with the environment
variable DC_TTY_MODE (see the ENVIRONMENT VARIABLES section).

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_MESSAGES.

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