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选题: 20190124 Orpie: A command-line reverse Polish notation calculator
sources/tech/20190124 Orpie- A command-line reverse Polish notation calculator.md
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[#]: collector: (lujun9972)
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[#]: translator: ( )
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Orpie: A command-line reverse Polish notation calculator)
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[#]: via: (https://opensource.com/article/19/1/orpie)
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[#]: author: (Peter Faller https://opensource.com/users/peterfaller)
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Orpie: A command-line reverse Polish notation calculator
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======
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Orpie is a scientific calculator that functions much like early, well-loved HP calculators.
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Orpie is a text-mode [reverse Polish notation][1] (RPN) calculator for the Linux console. It works very much like the early, well-loved Hewlett-Packard calculators.
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### Installing Orpie
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RPM and DEB packages are available for most distributions, so installation is just a matter of using either:
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```
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$ sudo apt install orpie
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```
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or
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```
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$ sudo yum install orpie
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```
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Orpie has a comprehensive man page; new users may want to have it open in another terminal window as they get started. Orpie can be customized for each user by editing the **~/.orpierc** configuration file. The [orpierc(5)][2] man page describes the contents of this file, and **/etc/orpierc** describes the default configuration.
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### Starting up
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Start Orpie by typing **orpie** at the command line. The main screen shows context-sensitive help on the left and the stack on the right. The cursor, where you enter numbers you want to calculate, is at the bottom-right corner.
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### Example calculation
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For a simple example, let's calculate the factorial of **5 (2 core.md Dict.md lctt2014.md lctt2016.md lctt2018.md LICENSE published README.md scripts sources translated 3 core.md Dict.md lctt2014.md lctt2016.md lctt2018.md LICENSE published README.md scripts sources translated 4 core.md Dict.md lctt2014.md lctt2016.md lctt2018.md LICENSE published README.md scripts sources translated 5)**. First the long way:
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| Keys | Result |
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| --------- | --------- |
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| 2 <enter> | Push 2 onto the stack |
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| 3 <enter> | Push 3 onto the stack |
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| * | Multiply to get 6 |
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| 4 <enter> | Push 4 onto the stack |
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| * | Multiply to get 24 |
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| 5 <enter> | Push 5 onto the stack |
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| * | Multiply to get 120 |
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Note that the multiplication happens as soon as you type *****. If you hit **< enter>** after ***** , Orpie will duplicate the value at position 1 on the stack. (If this happens, you can drop the duplicate with **\**.)
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Equivalent sequences are:
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| Keys | Result |
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| ------------- | ------------- |
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| 2 <enter> 3 * 4 * 5 * | Faster! |
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| 2 <enter> 3 <enter> 4 <enter> 5 * * * | Same result |
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| 5 <enter> ' fact <enter> | Fastest: Use the built-in function |
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Observe that when you enter **'** , the left pane changes to show matching functions as you type. In the example above, typing **fa** is enough to get the **fact** function. Orpie offers many functions—experiment by typing **'** and a few letters to see what's available.
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Note that each operation replaces one or more values on the stack. If you want to store the value at position 1 in the stack, key in (for example) **@factot <enter>** and **S'**. To retrieve the value, key in (for example) **@factot <enter>** then **;** (if you want to see it; otherwise just leave **@factot** as the value for the next calculation).
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### Constants and units
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Orpie understands units and predefines many useful scientific constants. For example, to calculate the energy in a blue light photon at 400nm, calculate **E=hc/(400nm)**. The key sequences are:
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| Keys | Result |
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| -------------- | -------------- |
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| C c <enter> | Get the speed of light in m/s |
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| C h <enter> | Get Planck's constant in Js |
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| * | Calculate h*c |
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| 400 <space> 9 n _ m | Input 4 _ 10^-9 m |
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| / | Do the division and get the result: 4.966 _ 10^-19 J |
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Like choosing functions after typing **'** , typing **C** shows matching constants based on what you type.
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### Matrices
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Orpie can also do operations with matrices. For example, to multiply two 2x2 matrices:
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| Keys | Result |
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| -------- | -------- |
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| [ 1 , 2 [ 3 , 4 <enter> | Stack contains the matrix [[ 1, 2 ][ 3, 4 ]] |
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| [ 1 , 0 [ 1 , 1 <enter> | Push the multiplier matrix onto the stack |
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| * | The result is: [[ 3, 2 ][ 7, 4 ]] |
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Note that the **]** characters are automatically inserted—entering **[** starts a new row.
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### Complex numbers
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Orpie can also calculate with complex numbers. They can be entered or displayed in either polar or rectangular form. You can toggle between the polar and rectangular display using the **p** key, and between degrees and radians using the **r** key. For example, to multiply **3 + 4i** by **4 + 4i** :
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| Keys | Result |
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| -------- | -------- |
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| ( 3 , 4 <enter> | The stack contains (3, 4) |
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| ( 4 , 4 <enter> | Push (4, 4) |
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| * | Get the result: (-4, 28) |
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Note that as you go, the results are kept on the stack so you can observe intermediate results in a lengthy calculation.
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### Quitting Orpie
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You can exit from Orpie by typing **Q**. Your state is saved, so the next time you start Orpie, you'll find the stack as you left it.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/19/1/orpie
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作者：[Peter Faller][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/peterfaller
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[b]: https://github.com/lujun9972
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[1]: https://en.wikipedia.org/wiki/Reverse_Polish_notation
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[2]: https://github.com/pelzlpj/orpie/blob/master/doc/orpierc.5
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