This is the first post of CLI App in C# series. This series aims to illustrate every detail of how to write a command tool in C#, based on .Net Core. I will explain most content from outlining an app, choosing a proper platform, packaging code into a single binary execute file to automating build in CICD.
- First, functions that will be included in demo App, technologies will be used and why use them.
- Second, most code in demo App.
- Last, packaging, how to build a final binary suitable for delivery.
So, let’s begin.
Introduction of demo App
If you use git as your daily version control tool, you will be familiar with the pattern of Command SubCommand Option, for example git push origin master / git clone https://github.com/torvalds/linux.git, we will create a demo App follows this pattern.
The primary function of the demo App will be to generate various numbers. It can generate different numbers depends on different subcommands and options. It is named gen and all the functions are included below.
| command | function | result |
|---|---|---|
gen mobile |
generate a random Chinese phone number | 15810885678 |
gen id |
generate a 18 bit Chinese ID number | 210765199707122345 |
gen id -l 110 |
generate a Chinese ID number has a prefix of 110 |
110765199707122345 |
gen id -s |
generate a 15 bit Chinese ID number | 456719970712234 |
gen -v |
print version info |
Introduction of Jargon
In the full command of gen id -l 110, there are some terms we use in command tool.
| command | Jargon |
|---|---|
gen |
Command |
id |
SubCommand |
-l |
Option |
'110' |
Verbs |
Technology Selection
Framework
We use dotnet core 2.1，which is the most recent LTS version of the .Net Core platform. It allows us to run our tool in not only Windows, but also macOS and Linux. We can use C# and develop very fast.
Parsing command line arguments
We will use CommandLineUtils to parse command line arguments. It is complicated and error-prone for us to use raw string[] args in main function to parse subcommands and options, so we choose a proper library to do dirty work for us.
CommandLineUtils forks from a library which is ASP.NET team developed for building dotnet cli applications. But years later the team thought it is out of their scope to develop such a library, so they archived the library. Fortunately, a developer from ASP.NET team has forked this repository in a private capacity, so we still have an actively developed and well-maintained library.
Packaging
The .Net Core’s command tool dotnet provide two subcommands for packaging: build and pack, they are used in build normal command line tool and build NuGet package(We can use NuGet package for the delivery of .Net Core Global Tool).
No matter which subcommands we use, we will get a bunch of .exe, .dll, and configuration files. We will use a tool named wrap, written in Rust, to build a final single .exe file from a bunch of files. It is more convenient for the user to deploy and use only one single file rather than one folder with various files.
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