How to use the command 'eva' (with examples)
The ’eva’ command is a simple calculator REPL (Read-Eval-Print Loop), similar to ‘bc’. It provides syntax highlighting and persistent history, making it easy to perform calculations in an interactive manner. This article will illustrate various use cases of the ’eva’ command and provide examples for each.
Use case 1: Run the calculator in interactive mode
Code:
eva
Motivation: Running the ’eva’ command without any arguments starts the calculator in interactive mode. This allows users to perform calculations and get immediate results without having to repeatedly invoke the ’eva’ command.
Explanation: The command ’eva’ is called without any additional arguments. This launches the calculator REPL in interactive mode, where users can enter mathematical expressions and evaluate them.
Example output:
Welcome to eva!
> 2 + 3
= 5
> 5 * 6
= 30
> sin(1)
= 0.841470984808
> exit
Use case 2: Calculate the result of an expression
Code:
eva "(1 + 2) * 2 ^ 2"
Motivation: This use case demonstrates how to use the ’eva’ command to directly calculate the result of a mathematical expression provided as an argument.
Explanation: The command ’eva’ is followed by the mathematical expression “(1 + 2) * 2 ^ 2”. The expression is evaluated and the result is printed.
Example output:
= 12
Use case 3: Calculate an expression forcing the number of decimal places to 5
Code:
eva --fix 5 "5 / 3"
Motivation: In certain scenarios, it may be necessary to control the number of decimal places in the calculated result. This use case demonstrates how to use the ‘–fix’ option to specify the desired number of decimal places.
Explanation: The command ’eva’ is followed by the ‘–fix’ option, which is used to specify the number of decimal places. In this example, the option is set to 5. The mathematical expression “5 / 3” is then evaluated, and the result is rounded to 5 decimal places.
Example output:
= 1.66667
Use case 4: Calculate an expression with sine and cosine
Code:
eva "sin(1) + cos(1)"
Motivation: The ’eva’ command supports various mathematical functions, including sine and cosine. This use case demonstrates how to use these functions within an expression.
Explanation: The command ’eva’ is followed by the mathematical expression “sin(1) + cos(1)”. The expressions ‘sin(1)’ and ‘cos(1)’ are evaluated separately, and the results are summed to provide the final result.
Example output:
= 1.38177329068
Conclusion:
The ’eva’ command provides a convenient REPL for performing mathematical calculations. It can be used in interactive mode, or specific mathematical expressions can be evaluated by providing them as arguments. The command also supports controlling the number of decimal places in the output and includes various mathematical functions like sine and cosine. With syntax highlighting and persistent history, ’eva’ makes it easy to perform calculations efficiently.
