Fli

Execute CLI commands from your F# code in F# style!

Fli is part of the F# Advent Calendar 2022: A little story about Fli

Features

• Starting processes easily
• Execute CLI commands in your favourite shell
• F# computation expression syntax
• Wrap authenticated CLI tools
• No external dependencies

Install

Get it from Nuget: dotnet add package Fli

Usage

open Fli and start

For example:

cli {
    Shell CMD
    Command "echo Hello World!"
}
|> Command.execute

that starts CMD.exe as Shell and echo Hello World! is the command to execute.

Run a file with PowerShell from a specific directory:

cli {
    Shell PWSH
    Command "test.bat"
    WorkingDirectory (Environment.GetFolderPath Environment.SpecialFolder.UserProfile)
}
|> Command.execute

Executing programs with arguments:

cli {
    Exec "path/to/executable"
    Arguments "--info"
}
|> Command.execute

an example with git:

cli {
    Exec "git"
    Arguments ["commit"; "-m"; "Fixing issue #1337."]
}
|> Command.execute

Add a verb to your executing program:

cli {
    Exec "adobe.exe"
    Arguments (Path.Combine ((Environment.GetFolderPath Environment.SpecialFolder.UserProfile), "test.pdf"))
    Verb "open"
}
|> Command.execute

or open a file in the default/assigned program:

cli {
    Exec "test.pdf"
}
|> Command.execute

(Hint: if file extension is not assigned to any installed program, it will throw a System.NullReferenceException)

Write output to a specific file:

cli {
    Exec "dotnet"
    Arguments "--list-sdks"
    Output @"absolute\path\to\dotnet-sdks.txt"
}
|> Command.execute

Write output to a function (logging, printing, etc.):

let log (output: string) = Debug.Log($"CLI log: {output}")

cli {
    Exec "dotnet"
    Arguments "--list-sdks"
    Output log
}
|> Command.execute

Add environment variables for the executing program:

cli {
    Exec "git"
    EnvironmentVariables [("GIT_AUTHOR_NAME", "Jon Doe"); ("GIT_AUTHOR_EMAIL", "[email protected]")]
}
|> Command.execute

Add credentials to program:

cli {
    Exec "program"
    Credentials ("domain", "bobk", "password123")
}
|> Command.execute

Hint: Running a process as a different user is supported on all platforms. Other options (Domain, Password) are only available on Windows. As an alternative for not Windows based systems there is:

cli {
    Exec "path/to/program"
    Username "admin"
}
|> Command.execute

Command.execute

Command.execute returns record: type Output = { Id: int; Text: string option; ExitCode: int; Error: string option } which has getter methods to get only one value:

toId: Output -> int
toText: Output -> string
toExitCode: Output -> int
toError: Output -> string

example:

cli {
    Shell CMD
    Command "echo Hello World!"
}
|> Command.execute // { Id = 123; Text = Some "Hello World!"; ExitCode = 0; Error = None }
|> Output.toText // "Hello World!"

// same with Output.toId:
cli { ... }
|> Command.execute // { Id = 123; Text = Some "Hello World!"; ExitCode = 0; Error = None }
|> Output.toId // 123

// same with Output.toExitCode:
cli { ... }
|> Command.execute // { Id = 123; Text = Some "Hello World!"; ExitCode = 0; Error = None }
|> Output.toExitCode // 0

// in case of an error:
cli { ... }
|> Command.execute // { Id = 123; Text = None; ExitCode = 1; Error = Some "This is an error!" }
|> Output.toError // "This is an error!"

Output functions

throwIfErrored: Output -> Output
throw: (Output -> bool) -> Output -> Output

Output.throw and Output.throwIfErrored are assertion functions that if something's not right it will throw an exception. That is useful for build scripts to stop the execution immediately, here is an example:

cli {
    Exec "dotnet"
    Arguments [| "build"; "-c"; "Release" |]
    WorkingDirectory "src/"
}
|> Command.execute // returns { Id = 123; Text = None; ExitCode = 1; Error = Some "This is an error!" }
|> Output.throwIfErrored // <- Exception thrown!
|> Output.toError

or, you can define when to "fail":

cli { ... }
|> Command.execute // returns { Id = 123; Text = "An error occured: ..."; ExitCode = 1; Error = Some "Error detail." }
|> Output.throw (fun output -> output.Text.Contains("error")) // <- Exception thrown!
|> Output.toError

Printing Output fields

There are printing methods in Output too:

printId: Output -> unit
printText: Output -> unit
printExitCode: Output -> unit
printError: Output -> unit

Instead of writing:

cli { ... }
|> Command.execute
|> Output.toText
|> printfn "%s"

For a little shorter code you can use:

cli { ... }
|> Command.execute
|> Output.printText

Command.toString

Command.toString concatenates only the the executing shell/program + the given commands/arguments:

cli {
    Shell PS
    Command "Write-Host Hello World!"
}
|> Command.toString // "powershell.exe -Command Write-Host Hello World!"

and:

cli {
    Exec "cmd.exe"
    Arguments [ "/C"; "echo"; "Hello World!" ]
}
|> Command.toString // "cmd.exe /C echo Hello World!"

Builder operations:

ShellContext operations (cli { Shell ... }):

ExecContext operations (cli { Exec ... }):

Currently provided Fli.Shells:

• CMD runs cmd.exe /c ... or cmd.exe /k ... (depends if Input is provided or not)
• PS runs powershell.exe -Command ...
• PWSH runs pwsh.exe -Command ...
• WSL runs wsl.exe -- ...
• BASH runs bash -c ...
• CUSTOM (shell: string * flag: string) runs the specified shell with the specified starting argument (flag)

Provided Fli.Outputs:

• File of string a string with an absolute path of the output file.
• StringBuilder of StringBuilder a StringBuilder which will be filled with the output text.
• Custom of Func<string, unit> a custom function (string -> unit) that will be called with the output string (logging, printing etc.).

Do you miss something?

Open an issue or start a discussion.

Inspiration

Use CE's for CLI commands came in mind while using FsHttp.