Function to list all functions within a script or scriptblock. Can then be piped to iex to effectively dot-source just the functions from a given file/block, or output to a file to concat a module of functions.

get-scriptfunctions.ps1

function Get-ScriptFunctions {
    <#
        .SYNOPSIS
            Lists all functions within a script or scriptblock.

        .DESCRIPTION
            Uses AST to retrieve all functions from a valid script file or 
            scriptblock, then outputs them all. Useful for dot-sourcing
            functions from a file that also contains running code.

        .EXAMPLE
            Get-ScriptFunctions -Export -ScriptPath .\testscript.ps1 | iex

        .EXAMPLE
            (Get-ScriptFunctions -ScriptPath .\testscript.ps1).Count
            7
    #>
    [CmdletBinding(DefaultParameterSetName='File')]
    [OutputType([System.Management.Automation.Language.ScriptBlockAst[]])]
    [OutputType([System.Management.Automation.Language.FunctionDefinitionAst[]])]
    param(
        # Filepath for script to analyse
        [Parameter(Mandatory, ValueFromPipelineByPropertyName, ParameterSetName = 'File')]
        [ValidateScript({Test-Path $_})]
        [Alias('FullName')]
        [IO.FileInfo[]]$ScriptPath,

        # Scriptblock to analyse
        [Parameter(Mandatory, ParameterSetName = 'Block')]
        [ScriptBlock[]]$ScriptBlock,

        # To export the functions alone, or with AST data
        [Switch]$Export
    )
    process {
        try {
            switch ($PSCmdlet.ParameterSetName) {
                'File'  {
                    Write-Verbose "Analysing [$ScriptPath]"
                    $Script = [System.Management.Automation.Language.Parser]::ParseFile($ScriptPath, [ref]$null, [ref]$null)
                }
                'Block' {
                    Write-Verbose "Analysing [ScriptBlock]"
                    $Script = [System.Management.Automation.Language.Parser]::ParseInput($ScriptBlock, [ref]$null, [ref]$null)
                }
            }
        } catch {
            throw "Failed to parse $($PSCmdlet.ParameterSetName).`n$_"
        }

        try {
            $functions = $Script.FindAll({$args[0] -is [System.Management.Automation.Language.FunctionDefinitionAst]}, $true)
            Write-Verbose "Found $($functions.count) functions: $($functions.Name -join ', ')"
        } catch {
            throw "Failed to find functions in $($PSCmdlet.ParameterSetName).`n$_"
        }

        if ($Export) {
            $functions.Extent
        } else {
            $functions
        }
    }
}