How to use the command 'dc' (with examples)

The command ‘dc’ is an arbitrary precision calculator that uses reverse polish notation (RPN). It allows you to perform calculations with high precision and provides various options to customize the behavior of the calculator.

Use case 1: Start an interactive session

Code:

dc

Motivation: Starting an interactive session allows you to perform calculations directly in the terminal. This is useful when you need to quickly calculate results or perform multiple calculations in succession.

Explanation: The command dc without any arguments starts an interactive session of the calculator. You can then enter expressions and perform calculations by following the reverse polish notation.

Example output:

$ dc
5 3 + p
8
10 2 / p
5

Use case 2: Execute a script

Code:

dc path/to/script.dc

Motivation: Executing a script allows you to perform complex calculations or repetitive tasks without manually entering each expression in the interactive session.

Explanation: The dc command can also execute a script file by providing the path to the script as an argument. The script file contains a set of expressions written in reverse polish notation, which are executed by the calculator in the order they appear in the file.

Example output: Suppose the script file script.dc contains the following expressions:

5 3 + p
10 2 / p

Executing the script with the command dc path/to/script.dc will produce the same output as the previous example:

$ dc path/to/script.dc
8
5

Use case 3: Calculate an expression with the specified scale

Code:

dc --expression='10 k 5 3 / p'

Motivation: Setting the scale allows you to control the number of decimal places in the calculations. This is useful when dealing with decimal numbers and you want to specify the level of precision.

Explanation: The --expression option followed by a string of expressions allows you to perform calculations directly on the command line. In this example, we set the scale to 10 decimal places using 10 k, then calculate the division of 5 by 3 and print the result using 5 3 / p.

Example output:

$ dc --expression='10 k 5 3 / p'
1.6666666667

Use case 4: Calculate 4 times 5, subtract 17, and print the output

Code:

dc --expression='4 5 * 17 - p'

Motivation: Performing calculations within the command line allows you to quickly obtain results without the need for external scripts or input files. This can be convenient when you only need a single calculation.

Explanation: This example demonstrates the use of arithmetic operators in reverse polish notation. The expression 4 5 * multiplies 4 and 5, then 17 - subtracts 17 from the result. Finally, p prints the output.

Example output:

$ dc --expression='4 5 * 17 - p'
3

Use case 5: Set number of decimal places to 7, calculate 5 divided by -3, and print

Code:

dc --expression='7 k 5 _3 / p'

Motivation: Changing the scale allows you to adjust the precision to suit the specific requirements of a calculation. In this example, we set the scale to 7 decimal places using 7 k before performing the division.

Explanation: By using the _3 notation instead of just 3, we indicate that the number 3 is a negative value. The division 5 _3 / calculates 5 divided by -3. The result is then printed using p.

Example output:

$ dc --expression='7 k 5 _3 / p'
-1.6666667

Use case 6: Calculate the golden ratio, phi

Code:

dc --expression='100 k 5 v 1 + 2 / p'

Motivation: The golden ratio, often referred to as phi, is a mathematical constant that commonly appears in various fields such as mathematics, nature, and art. Calculating the golden ratio with high precision can be useful in certain contexts.

Explanation: In this example, we calculate the golden ratio by applying the necessary operations step by step. First, we set the scale to 100 decimal places using 100 k. Then, 5 v calculates the square root of 5, 1 + adds 1 to the square root, 2 / divides the result by 2, and finally p prints the golden ratio.

Example output:

$ dc --expression='100 k 5 v 1 + 2 / p'
1.618033988749894848204586834365638117720309179805762862135448622705260462818902449707207204189391137484754088075386891752126633862223536931793180060766726354433389086595939582905638322661319928290267880675208766892501711696207032221043216269548626296313614438149758701220340805887954454749246185695364864449241032844301

Conclusion:

The dc command is a powerful and versatile tool for performing calculations in the command line. With its support for arbitrary precision and reverse polish notation, it provides a flexible and efficient way to perform mathematical operations. Whether you need to perform simple calculations or complex mathematical tasks, dc has the functionality to meet your needs.