dotnet sln add

dotnet sln add --help

eg@debian:~$ dotnet sln add --help
Description:
  Add one or more projects to a solution file.

Usage:
  dotnet sln <SLN_FILE> add [<PROJECT_PATH>...] [options]

Arguments:
  <SLN_FILE>      The solution file to operate on. If not specified, the command will search the current directory for one. [default: /home/eg/]
  <PROJECT_PATH>  The paths to the projects to add to the solution.

Options:
  --in-root                                Place project in root of the solution, rather than creating a solution folder.
  -s, --solution-folder <solution-folder>  The destination solution folder path to add the projects to.
  -?, -h, --help                           Show command line help.

dotnet sln <solution_file_path> add <project_file_path>

eg@debian:~$ dotnet sln ./Data/DotnetCliExamples/ExampleSolution/ExampleSolution.sln add ./Data/DotnetCliExamples/ExampleSolution/ExampleSolution.ConsoleApp1/ExampleSolution.ConsoleApp1.csproj
Project `ExampleSolution.ConsoleApp1/ExampleSolution.ConsoleApp1.csproj` added to the solution.