dc

Reverse-Polish calculator and one of the oldest Unix utilities.

	Command	Use
Printing
	p	print the stack top without altering the stack
	n	pops the stack top and prints it without a newline
	P	pops the stack top; if a string, print it without a newline; otherwise print the integer value as a byte stream
	f	print the entire stack top to bottom without altering anything
Arithmetic
	+	pops two values, adds them, and pushes the result
	-	pops two values, subtracts the first popped from the second, and pushes the result
	*	pops two values, multiplies them, and pushes the result
	/	pops two values, divides the second popped by the first, and pushes the result
	%	pops two values, calculates the remainder of the division that / would perform, and pushes that
	~	pops two values, divides the second popped by the first popped, then pushes the quotient followed by the remainder
	\		pops two values, raises the second popped to the power of the first popped, and pushes the result
	\		pops three values; the first popped is a reduction modulus, the third is the base, and the second is the exponent
	v	pops one value and computes its square root
Stack control
	c	clears the stack
	d	duplicates the value on top of the stack
	r	swaps the top two values on the stack
	R	pops the top value as an integer $n$, then rotates the top $n$ elements of the stack; if the stack has fewer than $n$ elements, the entire stack is rotated
Registers
	sr	pop the stack top and store it in register r
	lr	copy the value from register r and push it to the stack
	Sr	pop the top of the main stack and push it onto the stack of register r
	Lr	pop the top of register r's stack and push it onto the main stack
Parameters
	i	pops a value off the stack and uses it as the input radix
	o	pops a value off the stack and uses it as the output radix
	k	pops a value off the stack and uses it to set the precision
	I	pushes the current input radix onto the stack
	O	pushes the current output radix onto the stack
	K	pushes the current precision onto the stack
Strings
	[text]	pushes text to the stack as a string
	a	pops the top of stack; if it was a number, the low-order byte is converted to a string and pushed onto the stack; otherwise, the first character of the string is pushed back
	x	pops a value off the stack and executes it as a macro; if the stack top was a number, it is simply pushed back
	>r	pops two values and compares them as numbers, then executes the contents of r as a macro if the first popped is greater than the second
	!>r	similar, but invokes the macro if the first popped is not greater than the second
	<r	similar, but invokes the macro if the first popped is less than the second
	!<r	similar, but invokes the macro if the first popped is not less than the second
	=r	similar, but invokes the macro if the two numbers are equal
	!=r	similar, but invokes the macro if the two numbers are not equal
	?	reads a line from the terminal and executes it, allowing for user input
	q	exits from a macro and from the macro which invoked it; if called from the top level, exits dc
	Q	pops a value off the stack and uses it as a count of macro levels to exit; will never cause dc to exit
Status inquiry
	Z	pops a value off the stack, calculates the number of decimal digits (or number of characters if a string) it has, and pushes that number; this does not include any leading zeros
	X	pops a value off the stack, calculates the number of fraction digits it has, and pushes that number; if a string, the value pushed is 0
	z	pushes the current stack depth
Miscellaneous
	!	executes the rest of the line as a system command; if the command begins with <, =, or >, then a space must be present after the !
	#	interprets the rest of the line as a comment
	:r	pops the top two values off the stack, storing the second popped in the array r, indexed by the first popped
	;r	pops the top of stack and uses it as an index into array r; the selected value is then pushed onto the stack