Converts a PowerShell object to a Markdown table.

ConvertTo-Markdown.ps1

<#
.Synopsis
   Converts a PowerShell object to a Markdown table.
.EXAMPLE
   $data | ConvertTo-Markdown
.EXAMPLE
   ConvertTo-Markdown($data)
#>
Function ConvertTo-Markdown {
    [CmdletBinding()]
    [OutputType([string])]
    Param (
        [Parameter(
            Mandatory = $true,
            Position = 0,
            ValueFromPipeline = $true
        )]
        [PSObject[]]$collection
    )

    Begin {
        $items = @()
        $columns = @{}
    }

    Process {
        ForEach($item in $collection) {
            $items += $item

            $item.PSObject.Properties | %{
                if(-not $columns.ContainsKey($_.Name) -or $columns[$_.Name] -lt $_.Value.ToString().Length) {
                    $columns[$_.Name] = $_.Value.ToString().Length
                }
            }
        }
    }

    End {
        ForEach($key in $($columns.Keys)) {
            $columns[$key] = [Math]::Max($columns[$key], $key.Length)
        }

        $header = @()
        ForEach($key in $columns.Keys) {
            $header += ('{0,-' + $columns[$key] + '}') -f $key
        }
        $header -join ' | '

        $separator = @()
        ForEach($key in $columns.Keys) {
            $separator += '-' * $columns[$key]
        }
        $separator -join ' | '

        ForEach($item in $items) {
            $values = @()
            ForEach($key in $columns.Keys) {
                $values += ('{0,-' + $columns[$key] + '}') -f $item.($key)
            }
            $values -join ' | '
        }
    }
}

For anyone that stumbles upon this in the future, I modified the function to do the following extra things

• Handle null values
• Be an ordered list, so the properties will be listed in the order they are in the PS object
• Add | before and after each line, to comply with markdownlint rules
• Converted it to use generic lists instead of += for a lot more speed on large objects

Hope it helps someone!

Function ConvertTo-Markdown {
    [CmdletBinding()]
    [OutputType([string])]
    Param (
        [Parameter(
            Mandatory = $true,
            Position = 0,
            ValueFromPipeline = $true
        )]
        [PSObject[]]$collection
    )

    Begin {
        $items = [System.Collections.Generic.List[System.Object]]::new()
        $columns = [ordered]@{}
    }

    Process {
        ForEach ($item in $collection) {
            $items.Add($item)

            $item.PSObject.Properties | ForEach-Object {
                if ($null -ne $_.Value ) {
                    if (-not $columns.Contains($_.Name) -or $columns[$_.Name] -lt $_.Value.ToString().Length) {
                        $columns[$_.Name] = $_.Value.ToString().Length
                    }
                } else {
                    # Add the property to the columns, even if it's empty. If this is not done, the property will be missing from the output if it's null in all the values in the collection
                    $columns[$_.Name] = ' '
                }
            }
        }
    }

    End {
        foreach ($key in $($columns.Keys)) {
            $columns[$key] = [Math]::Max($columns[$key], $key.Length)
        }

        $header = [System.Collections.Generic.List[System.Object]]::new()
        foreach ($key in $columns.Keys) {
            $header.Add((('{0,-' + $columns[$key] + '}') -f $key))
        }
        # Make markdown header row
        Write-Output "| $($header -join ' | ') |"

        $separator = [System.Collections.Generic.List[System.Object]]::new()
        foreach ($key in $columns.Keys) {
            $separator.Add(('-' * $columns[$key]))
        }
        # Make markdown separator row
        Write-Output "| $($separator -join ' | ')  |"

        foreach ($item in $items) {
            $values = [System.Collections.Generic.List[System.Object]]::new()
            foreach ($key in $columns.Keys) {
                $values.Add((('{0,-' + $columns[$key] + '}') -f $item.($key)))
            }
            # Make all the values into a table rows
            Write-Output "| $($values -join ' | ') |"
        }
    }
}