man dcで確認できるマニュアルを読破してdcコマンドを完全に使いこなせるようにしたいと思います。
書き始め記事です。
dc(1) General Commands Manual dc(1)
NAME
dc - an arbitrary precision calculator
SYNOPSIS
dc [-V] [--version] [-h] [--help]
[-e scriptexpression] [--expression=scriptexpression]
[-f scriptfile] [--file=scriptfile]
[file ...]
任意精度の計算機ってことですが、なぜdcって名前か分かりません。
使いそうなオプションは、-eと-fですね。
DESCRIPTION
dc is a reverse-polish desk calculator which supports unlimited preci‐
sion arithmetic. It also allows you to define and call macros. Nor‐
mally dc reads from the standard input; if any command arguments are
given to it, they are filenames, and dc reads and executes the contents
of the files before reading from standard input. All normal output is
to standard output; all error output is to standard error.
A reverse-polish calculator stores numbers on a stack. Entering a num‐
ber pushes it on the stack. Arithmetic operations pop arguments off
the stack and push the results.
To enter a number in dc, type the digits (using upper case letters A
through F as "digits" when working with input bases greater than ten),
with an optional decimal point. Exponential notation is not supported.
To enter a negative number, begin the number with ``_''. ``-'' cannot
be used for this, as it is a binary operator for subtraction instead.
To enter two numbers in succession, separate them with spaces or new‐
lines. These have no meaning as commands.
任意精度の逆ポーランド表記の電卓で、マクロも使えてしまう。いかにもすごい電卓っぽいですね。
標準入力が使えるようです。
ちょっと確認してみます。
takk~$ echo 10p | dc 10 takk~$
スタックに10を積んで、スタックの一番を、pコマンドで表示してみました。
10が表示されましたね。
足し算をしてみます。
takk~$ echo 10 20 +p | dc 30 takk~$
これは面白いですねえ。
では、man dcのマニュアルにしたがってオプションを確認していきます。
OPTIONS
dc may be invoked with the following command-line options:
-V
--version
Print out the version of dc that is being run and a copyright
notice, then exit.
バージョン表示ですね。ロングオプションの方も、ショートと同じなので省略しまｓ。
takk~$ dc -V dc (GNU bc 1.07.1) 1.4.1 Copyright 1994, 1997, 1998, 2000, 2001, 2003-2006, 2008, 2010, 2012-2017 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE, to the extent permitted by law.
次は、ヘルプです。
-h
--help Print a usage message briefly summarizing these command-line op‐
tions and the bug-reporting address, then exit.
こちらもショートオプションだけ確認します。
takk~$ dc -h Usage: dc [OPTION] [file ...] -e, --expression=EXPR evaluate expression -f, --file=FILE evaluate contents of file -h, --help display this help and exit -V, --version output version information and exit Email bug reports to: bug-dc@gnu.org . takk~$
ふむふむ。忘れなさそうなオプションだけが表示されるヘルプですねえ。
次は-eオプション。スクリプト指定といえば、たいてい-eですね。
-e script
--expression=script
Add the commands in script to the set of commands to be run
while processing the input.
スクリプトを直接指定できるんですね。
takk~$ dc -e '10 20 +p' 30 takk~$
標準入力とどちらか打ち込みが楽でしょうか。
takk~$ dc <<< '10 20 +p' 30 takk~$
ビミョーなところです。
-f script-file
--file=script-file
Add the commands contained in the file script-file to the set of
commands to be run while processing the input.
スクリプトファイルが使えるとのこと。
使ってみます。
takk~$ cat a.txt 10 20 + p takk~$ dc -f a.txt 30 takk~$
スクリプトファイルだと、後から計算式を見直すのに効率がよさそうです。
If any command-line parameters remain after processing the above, these
parameters are interpreted as the names of input files to be processed.
A file name of - refers to the standard input stream. The standard in‐
put will processed if no script files or expressions are specified.
すでに使い方が分かってたので先走りましたが、ここに使い方が書いてありますね。
では各オプションです。
Printing Commands
p Prints the value on the top of the stack, without altering the
stack. A newline is printed after the value.
変更せずにスタックの一番上の値を表示だけしてくれます。
takk~$ dc <<< '10 20 30 ppp' 30 30 30 takk~$
pを3回実行しても、スタックを更新しないので、同じ値が3回表示されました。
n Prints the value on the top of the stack, popping it off, and
does not print a newline after.
次はスタックを取り出して表示するコマンドです。
takk~$ dc <<< '10 20 30 nnn' 302010takk~$
スタックの一番上から順に取り出して表示されました。改行は表示されません。
P Pops off the value on top of the stack. If it it a string, it
is simply printed without a trailing newline. Otherwise it is a
number, and the integer portion of its absolute value is printed
out as a "base (UCHAR_MAX+1)" byte stream. Assuming that
(UCHAR_MAX+1) is 256 (as it is on most machines with 8-bit
bytes), the sequence KSK0k1/_1Ss [ls*]Sxd0>x
[256~Ssd0<x]dsxxsx[q]Sq[Lsd0>qaPlxx] dsxxsx0sqLqsxLxLK+k could
also accomplish this function. (Much of the complexity of the
above native-dc code is due to the ~ computing the characters
backwards, and the desire to ensure that all registers wind up
back in their original states.)
文字列は、文字列は[]で囲みます。Pで文字列を表示すると改行されません。 takk~$ dc <<< '[HELLO] P' HELLOtakk~$
f Prints the entire contents of the stack without altering any‐
thing. This is a good command to use if you are lost or want to
figure out what the effect of some command has been.
全スタックを表示するコマンドですね。
takk~$ dc <<< '10 20 30 f' 30 20 10 takk~$
Arithmetic
+ Pops two values off the stack, adds them, and pushes the result.
The precision of the result is determined only by the values of
the arguments, and is enough to be exact.
一番上と二つ目のスタックを加算してくれるコマンドです。
takk~$ dc <<< '10 20 30 +f' 50 10 takk~$
加算された20と30が消えて、計算結果である50がスタックの一番上に積まれました。
次は減算です。
- Pops two values, subtracts the first one popped from the second
one popped, and pushes the result.
5 – 3を計算してみます。
takk~$ dc <<< '5 3 -p' 2 takk~$
次は乗算。
* Pops two values, multiplies them, and pushes the result. The
number of fraction digits in the result depends on the current
precision value and the number of fraction digits in the two ar‐
guments.
11 * 20です。
takk~$ dc <<< '11 20 *p' 220 takk~$
除算です。
/ Pops two values, divides the second one popped from the first
one popped, and pushes the result. The number of fraction dig‐
its is specified by the precision value.
30 ÷ 2です。
takk~$ dc <<< '30 2 /p' 15 takk~$
次は、余を求めます。
% Pops two values, computes the remainder of the division that the
/ command would do, and pushes that. The value computed is the
same as that computed by the sequence Sd dld/ Ld*- .
5÷3の余りです。
takk~$ dc <<< '5 3 %p' 2 takk~$
商と余を同時に求めます。
~ Pops two values, divides the second one popped from the first
one popped. The quotient is pushed first, and the remainder is
pushed next. The number of fraction digits used in the division
is specified by the precision value. (The sequence SdSn lnld/
LnLd% could also accomplish this function, with slightly differ‐
ent error checking.)
20 ÷ 3を実行してみます。
takk~$ dc <<< '20 3 ~f' 2 6 takk~$
一番上のスタックが余、二つ目に商が格納されます。
次は指数計算です。
^ Pops two values and exponentiates, using the first value popped
as the exponent and the second popped as the base. The fraction
part of the exponent is ignored. The precision value specifies
the number of fraction digits in the result.
一番上のスタックが指数で、二つ目が底になります。
2の8乗を計算してみます。
takk~$ dc <<<'2 8 ^p' 256 takk~$
| Pops three values and computes a modular exponentiation. The
first value popped is used as the reduction modulus; this value
must be a non-zero number, and should be an integer. The second
popped is used as the exponent; this value must be a non-nega‐
tive number, and any fractional part of this exponent will be
ignored. The third value popped is the base which gets exponen‐
tiated, which should be an integer. For small integers this is
like the sequence Sm^Lm%, but, unlike ^, this command will work
with arbitrarily large exponents.
冪剰余(べきじょうよ)ですね。
一番上が法、二番目が冪指数、三番目が底です。
13の2乗を5で割った余を求めてみます。
takk~$ dc <<<'13 2 5 |p' 4 takk~$
v Pops one value, computes its square root, and pushes that. The
maximum of the precision value and the precision of the argument
is used to determine the number of fraction digits in the re‐
sult.
平方根です。9と25と36それぞれの平方根を求めます。
takk~$ dc <<<'9vp 25vp 36vp' 3 5 6 takk~$
結果が無理数となる場合はどうでしょうか。
2の平方根を求めてみます。
takk~$ dc <<<'2vp' 1 takk~$
1.4142…とはならずに、1が返りました。
Most arithmetic operations are affected by the ``precision value'',
which you can set with the k command. The default precision value is
zero, which means that all arithmetic except for addition and subtrac‐
tion produces integer results.
kコマンドで精度を変えられるが、初期精度は整数になっているようです(k=0)。
さきほどの2の平方根の結果も、精度を変更すれば小数点以下が返ってくるということですね。
takk~$ dc <<<'5k 2vp' 1.41421 takk~$
次はスタック制御です。
Stack Control
c Clears the stack, rendering it empty.
d Duplicates the value on the top of the stack, pushing another
copy of it. Thus, ``4d*p'' computes 4 squared and prints it.
r Reverses the order of (swaps) the top two values on the stack.
(This can also be accomplished with the sequence SaSbLaLb.)
R Pops the top-of-stack as an integer n. Cyclically rotates the
top n items on the updated stack. If n is positive, then the
rotation direction will make the topmost element the second-from
top; if n is negative, then the rotation will make the topmost
element the n-th element from the top. If the stack depth is
less than n, then the entire stack is rotated (in the appropri‐
ate direction), without any error being reported.
Registers
dc provides at least 256 memory registers, each named by a single char‐
acter. You can store a number or a string in a register and retrieve
it later.
sr Pop the value off the top of the stack and store it into regis‐
ter r.
lr Copy the value in register r and push it onto the stack. The
value 0 is retrieved if the register is uninitialized. This
does not alter the contents of r.
Each register also contains its own stack. The current register value
is the top of the register's stack.
Sr Pop the value off the top of the (main) stack and push it onto
the stack of register r. The previous value of the register be‐
comes inaccessible.
Lr Pop the value off the top of register r's stack and push it onto
the main stack. The previous value in register r's stack, if
any, is now accessible via the lr command.
Parameters
dc has three parameters that control its operation: the precision, the
input radix, and the output radix. The precision specifies the number
of fraction digits to keep in the result of most arithmetic operations.
The input radix controls the interpretation of numbers typed in; all
numbers typed in use this radix. The output radix is used for printing
numbers.
The input and output radices are separate parameters; you can make them
unequal, which can be useful or confusing. The input radix must be be‐
tween 2 and 16 inclusive. The output radix must be at least 2. The
precision must be zero or greater. The precision is always measured in
decimal digits, regardless of the current input or output radix.
i Pops the value off the top of the stack and uses it to set the
input radix.
o Pops the value off the top of the stack and uses it to set the
output radix.
k Pops the value off the top of the stack and uses it to set the
precision.
I Pushes the current input radix on the stack.
O Pushes the current output radix on the stack.
K Pushes the current precision on the stack.
Strings
dc has a limited ability to operate on strings as well as on numbers;
the only things you can do with strings are print them and execute them
as macros (which means that the contents of the string are processed as
dc commands). All registers and the stack can hold strings, and dc al‐
ways knows whether any given object is a string or a number. Some com‐
mands such as arithmetic operations demand numbers as arguments and
print errors if given strings. Other commands can accept either a num‐
ber or a string; for example, the p command can accept either and
prints the object according to its type.
[characters]
Makes a string containing characters (contained between balanced
[ and ] characters), and pushes it on the stack. For example,
[foo]P prints the characters foo (with no newline).
a The top-of-stack is popped. If it was a number, then the low-
order byte of this number is converted into a string and pushed
onto the stack. Otherwise the top-of-stack was a string, and
the first character of that string is pushed back.
x Pops a value off the stack and executes it as a macro. Normally
it should be a string; if it is a number, it is simply pushed
back onto the stack. For example, [1p]x executes the macro 1p
which pushes 1 on the stack and prints 1 on a separate line.
Macros are most often stored in registers; [1p]sa stores a macro to
print 1 into register a, and lax invokes this macro.
>r Pops two values off the stack and compares them assuming they
are numbers, executing the contents of register r as a macro if
the original top-of-stack is greater. Thus, 1 2>a will invoke
register a's contents and 2 1>a will not.
!>r Similar but invokes the macro if the original top-of-stack is
not greater than (less than or equal to) what was the second-to-
top.
<r Similar but invokes the macro if the original top-of-stack is
less.
!<r Similar but invokes the macro if the original top-of-stack is
not less than (greater than or equal to) what was the second-to-
top.
=r Similar but invokes the macro if the two numbers popped are
equal.
!=r Similar but invokes the macro if the two numbers popped are not
equal.
? Reads a line from the terminal and executes it. This command
allows a macro to request input from the user.
q exits from a macro and also from the macro which invoked it. If
called from the top level, or from a macro which was called di‐
rectly from the top level, the q command will cause dc to exit.
Q Pops a value off the stack and uses it as a count of levels of
macro execution to be exited. Thus, 3Q exits three levels. The
Q command will never cause dc to exit.
Status Inquiry
Z Pops a value off the stack, calculates the number of decimal
digits it has (or number of characters, if it is a string) and
pushes that number. The digit count for a number does not in‐
clude any leading zeros, even if those appear to the right of
the radix point.
X Pops a value off the stack, calculates the number of fraction
digits it has, and pushes that number. For a string, the value
pushed is 0.
z Pushes the current stack depth: the number of objects on the
stack before the execution of the z command.
Miscellaneous
! Will run the rest of the line as a system command. Note that
parsing of the !<, !=, and !> commands take precedence, so if
you want to run a command starting with <, =, or > you will need
to add a space after the !.
# Will interpret the rest of the line as a comment.
:r Will pop the top two values off of the stack. The old second-
to-top value will be stored in the array r, indexed by the old
top-of-stack value.
;r Pops the top-of-stack and uses it as an index into the array r.
The selected value is then pushed onto the stack.
Note that each stacked instance of a register has its own array associ‐
ated with it. Thus 1 0:a 0Sa 2 0:a La 0;ap will print 1, because the 2
was stored in an instance of 0:a that was later popped.
FILES
~/.dcrc The commands in this file will be executed when dc is
first run.
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