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### ANSI VT100 colors in Powershell Core prompt

October 19, 2018 — Jesse Harris

Sometime ago I was searching the interwebs for inspiration to spruce up my powershell prompt. I came across someone's prompt they shared on stackoverflow or superuser and unfortunatly I could not find the link again to give proper credit.

Today, I'm essentially using the same prompt but I've had to adjust it to work on Windows and MacOS with the two areas of compatability being that Windows uses backslash `\` and Unixes like GNU/Linux and MacOS use forwardslash `/`.

With Windows powershell, in order to get colorized text, you had to use the `Write-Host` commandlet, but when switching to PSCore, the same code produced strange results. Initially the prompt would look fine, but if you were in a deep path, as soon as you typed a key, much of the prompt would be overwritten or word or some letters would be duplicated.

After a bit of research I found the Windows Console had had VT100 escape sequence support added. You could, in theory, enable any Windows 10 1607+ console to support VT100, but you would need to use the WinAPI SetConsoleMode

It turns out, that PSCore on Windows, does this very thing, and so without any extra work, VT100 escape sequences work out of the box on this.

        function ConvertTo-ShortPath {
            Param([string]$Path)
            # Replace Home with ~ symbol
            $Location = $Path.Replace($HOME, '~')
            # Remove prefix for UNC paths
            $Location = $Location -replace '^[^:]+::', ''
            # Handle paths starting with \\ and . correctly
            # For paths not the current directory, display only a single
            #   character for each directory in the tree
            If ($IsMacOS -or $IsLinux) {
                # Systems with / paths
                $Location = $Location -replace '(.?)([^/])[^/]*(?=/)','$1$2'
            } else {
                # Systems with \ paths
                $Location = $Location -replace '\\(\.?)([^\\])[^\\]*(?=\\)','\$1$2'
            }
            return $Location
        }

        function prompt {
            If ($PSEdition -eq "Core") {
                $BC = "`e[96m" #Bright Cyan
                $C = "`e[36m" #Cyan
                $G = "`e[32m" #Green
                $N = "`e[0m" #No Color
            } else {
                $C = [ConsoleColor]::DarkCyan
                $G = [ConsoleColor]::Green
                $BC = [ConsoleColor]::Cyan
            }

            $root = [char]0x0E3
            $nonroot = [char]0x0A7
            $H = $([net.dns]::GetHostName())

            if (Test-CurrentAdminRights) {
                $priv = $root
            } else {
                $priv = $nonroot
            }

            if ($PSEdition -eq "Core"){
                # PSCore doesn't like a prompt using Write-Host
                #   thankfully, using VT100 signals works fine
                "${BC}${priv} $G$H $C{ $BC$(ConvertTo-ShortPath ((pwd).Path)) $C }$N "
            } else {
                Write-Host "$priv " -NoNewline -ForegroundColor $BC
                Write-Host $H -NoNewline -ForegroundColor $G
                Write-Host ' {' -NoNewline -ForegroundColor $C
                Write-Host (ConvertTo-ShortPath (pwd).Path) -NoNewline -ForegroundColor $BC
                Write-Host '}' -NoNewline -ForegroundColor $C
                return ' '
            }
        }

Tags: vt100, powershell, profile