setup-local-sdk

setup-local-sdk

Purpose

Guide the user through installing a .NET SDK into a project-local .dotnet/ directory and wiring it up via the global.json paths feature (.NET 10+). The examples use .NET 11, but this works with any version — prerelease or stable.

The result is a fully isolated SDK that:

• Does not modify the system-wide .NET installation.
• Is picked up automatically by dotnet commands from the project root.
• Can be deleted to revert (rm -rf .dotnet/ or Remove-Item -Recurse -Force .\.dotnet).

When NOT to use

• User wants a system-wide install — direct to the official installer.
• Host dotnet is older than v10 — paths doesn't exist; explain and stop.
• User needs a runtime-only install — paths applies to SDK resolution only.

Inputs / Prerequisites

Input	Required	Default	Notes
Channel or version	No	11.0	e.g. 11.0, STS, LTS, or an exact version like 11.0.100-preview.2.26159.112
Quality	No	preview	One of: daily, preview, ga
jq	No	—	Optional for bash team scripts when patching an existing global.json; without it, do not overwrite the file

Prerequisites

1. A .NET 10+ SDK is installed globally — run dotnet --version; major ≥ 10.
2. curl (macOS/Linux) or PowerShell (Windows) is available.

Workflow

Step 1 — Clarify what to install

If the user didn't specify, ask what .NET SDK version they want (e.g., "latest .NET 11 preview" or an exact version like 11.0.100-preview.2.26159.112). Map the answer to --channel/--quality or --version flags.

Step 2 — Verify .NET 10+ host

If the user already provided dotnet --version output, treat that as the authoritative version for their machine. Do not override it with the agent workspace's version; if the two differ, explain that the workspace differs and continue advising for the user's machine.

dotnet --version

If major version < 10, stop before downloading anything: the paths feature requires a .NET 10+ host SDK. Tell the user to install .NET 10 or later system-wide first, then return to the local SDK setup.

Step 3 — Detect operating system

Run uname -s 2>/dev/null. If it succeeds (including MINGW*, MSYS*, CYGWIN* — these are bash-capable environments like Git Bash) → use bash/dotnet-install.sh. If it fails (native Windows without Git Bash) → use PowerShell/dotnet-install.ps1.

Step 4 — Check for existing local SDK

macOS / Linux:

test -d .dotnet && echo "exists" || echo "not found"

Windows (PowerShell):

if (Test-Path -LiteralPath .\.dotnet) { "exists" } else { "not found" }

If .dotnet/ exists, ask: update with the new version, or skip and keep it?

Step 5 — Download and run the install script

macOS / Linux:

INSTALL_SCRIPT="$(mktemp "${TMPDIR:-/tmp}/dotnet-install.XXXXXX")"
trap 'rm -f "$INSTALL_SCRIPT"' EXIT
curl -fsSL https://dot.net/v1/dotnet-install.sh -o "$INSTALL_SCRIPT"
bash "$INSTALL_SCRIPT" --channel <CHANNEL> --quality <QUALITY> --install-dir .dotnet

Windows (PowerShell):

$installScript = Join-Path $env:TEMP "dotnet-install-$([guid]::NewGuid()).ps1"
try {
    Invoke-WebRequest -Uri 'https://dot.net/v1/dotnet-install.ps1' -OutFile $installScript
    & $installScript -Channel <CHANNEL> -Quality <QUALITY> -InstallDir .dotnet
}
finally {
    if (Test-Path -LiteralPath $installScript) {
        Remove-Item -LiteralPath $installScript -Force
    }
}

For exact versions: use --version <VERSION> (bash) or -Version <VERSION> (PowerShell) instead of channel/quality flags. The install scripts are from Microsoft's official URLs: https://dot.net/v1/dotnet-install.sh and https://dot.net/v1/dotnet-install.ps1.

Step 6 — Identify the installed version

./.dotnet/dotnet --version          # macOS/Linux
.\.dotnet\dotnet.exe --version      # Windows

Record the exact version string (e.g., 11.0.100-preview.2.26159.112) for global.json.

Step 7 — Create or update global.json

{
  "sdk": {
    "version": "<INSTALLED_VERSION>",
    "allowPrerelease": true,
    "rollForward": "latestFeature",
    "paths": [".dotnet", "$host$"],
    "errorMessage": "Required .NET SDK not found. Run ./install-dotnet.sh (or .ps1) to install it locally."
  }
}

• paths: .dotnet first (local priority), $host$ = system-wide fallback.
• rollForward: "latestFeature": use for latest-preview or floating feature-band installs.
• Exact version requests: use rollForward: "disable" so SDK resolution doesn't move to a different feature band.
• allowPrerelease: set to true only when installing a prerelease SDK. Omit for stable versions.
• errorMessage: include only when team install scripts are created (Step 10). Otherwise omit.

If global.json already exists, merge carefully: preserve existing properties (msbuild-sdks, tools, etc.) and only add/update the sdk section. Read the existing file first, update/add the sdk object, then write it back. This ensures cross-project config (e.g., MSBuild settings) isn't lost. Always back up the original file (e.g., global.json.bak) before modifying.

Minimal config (when version pinning isn't needed): {"sdk":{"paths":[".dotnet","$host$"]}}

Step 8 — Update .gitignore

macOS / Linux (or Git Bash):

grep -qxF '.dotnet/' .gitignore 2>/dev/null || printf '\n.dotnet/\n' >> .gitignore

Windows (PowerShell):

if (-not (Test-Path .gitignore) -or -not (Select-String -Path .gitignore -Pattern '^\.dotnet/$' -Quiet)) {
    Add-Content -Path .gitignore -Value '.dotnet/'
}

Step 9 — Install workloads (if requested)

Only do this after global.json and .gitignore are complete, so a slow or platform-limited workload install does not prevent the base local SDK setup from being usable.

If the user mentioned MAUI, mobile, workload, Blazor WASM, or cross-platform, install using the local binary (no sudo needed):

./.dotnet/dotnet workload install <workload>       # macOS/Linux
.\.dotnet\dotnet.exe workload install <workload>   # Windows

Verify: ./.dotnet/dotnet workload list (or .\.dotnet\dotnet.exe workload list).

For MAUI, pick a workload supported by the current OS and target platform. On Linux, the full maui meta-workload is not available; use a supported workload such as maui-android when Android is the target, or explain the platform limitation and ask which target to configure.

Always use the local dotnet binary for workload commands. Workload metadata is stored relative to the host process's dotnet root. The system dotnet puts metadata in the wrong location. (See dotnet/sdk#49825.)

Step 10 — Create team install scripts

Create if user mentioned "team", "share", "CI", "scripts", etc. Otherwise offer. These examples back up global.json and preserve existing settings. The bash script uses jq when an existing global.json must be patched; if jq is unavailable, it refuses to overwrite the file and prints the settings to merge manually. Adapt script variables to the install choice from Step 1: exact versions should use --version / -Version and rollForward: "disable"; channel installs should use channel/quality and only set allowPrerelease: true for prerelease SDKs. If global.json already pins sdk.version and the user mainly needs team scripts, reuse that version in the scripts and update global.json first; do not start a long SDK download just to discover the version. When the user asks for both setup and scripts, create the scripts/config before any long install so the reproducible setup exists even if download or workload installation is slow.

install-dotnet.sh:

#!/usr/bin/env bash
set -euo pipefail
INSTALL_DIR=".dotnet"
CHANNEL="11.0"
QUALITY="preview"
VERSION=""
ROLL_FORWARD="latestFeature"
ALLOW_PRERELEASE="true"
WORKLOADS=("${@}")
ERROR_MESSAGE="Required .NET SDK not found. Run ./install-dotnet.sh (or .ps1) to install it locally."
INSTALL_SCRIPT="$(mktemp "${TMPDIR:-/tmp}/dotnet-install.XXXXXX")"
GLOBAL_JSON_TMP=""
cleanup() {
    rm -f "$INSTALL_SCRIPT"
    [ -n "$GLOBAL_JSON_TMP" ] && rm -f "$GLOBAL_JSON_TMP"
}
trap cleanup EXIT
curl -fsSL https://dot.net/v1/dotnet-install.sh -o "$INSTALL_SCRIPT"
INSTALL_ARGS=(--install-dir "$INSTALL_DIR")
if [ -n "$VERSION" ]; then
    INSTALL_ARGS+=(--version "$VERSION")
    ROLL_FORWARD="disable"
else
    INSTALL_ARGS+=(--channel "$CHANNEL" --quality "$QUALITY")
fi
bash "$INSTALL_SCRIPT" "${INSTALL_ARGS[@]}"
SDK_VERSION=$("$INSTALL_DIR/dotnet" --version)
write_global_json() {
    if [ -f global.json ]; then
        cp global.json global.json.bak
        if ! command -v jq >/dev/null 2>&1; then
            echo "global.json exists; install succeeded, but this script will not overwrite it without jq." >&2
            echo "Merge these sdk settings manually so existing global.json properties are preserved:" >&2
            cat >&2 <<EOF
{
  "sdk": {
    "version": "$SDK_VERSION",
    "allowPrerelease": $ALLOW_PRERELEASE,
    "rollForward": "$ROLL_FORWARD",
    "paths": [".dotnet", "\$host\$"],
    "errorMessage": "$ERROR_MESSAGE"
  }
}
EOF
            exit 1
        fi
        GLOBAL_JSON_TMP="$(mktemp "${TMPDIR:-/tmp}/global-json.XXXXXX")"
        jq --arg version "$SDK_VERSION" --arg rollForward "$ROLL_FORWARD" --argjson allowPrerelease "$ALLOW_PRERELEASE" --arg errorMessage "$ERROR_MESSAGE" '
          .sdk = ((.sdk // {}) + {
            version: $version,
            allowPrerelease: $allowPrerelease,
            rollForward: $rollForward,
            paths: [".dotnet", "$host$"],
            errorMessage: $errorMessage
          })
        ' global.json > "$GLOBAL_JSON_TMP"
        mv "$GLOBAL_JSON_TMP" global.json
        GLOBAL_JSON_TMP=""
    else
        cat > global.json <<EOF
{
  "sdk": {
    "version": "$SDK_VERSION",
    "allowPrerelease": $ALLOW_PRERELEASE,
    "rollForward": "$ROLL_FORWARD",
    "paths": [".dotnet", "\$host\$"],
    "errorMessage": "$ERROR_MESSAGE"
  }
}
EOF
    fi
}
write_global_json
grep -qxF '.dotnet/' .gitignore 2>/dev/null || printf '\n.dotnet/\n' >> .gitignore
[ ${#WORKLOADS[@]} -gt 0 ] && "$INSTALL_DIR/dotnet" workload install "${WORKLOADS[@]}"
echo "Done. SDK: $SDK_VERSION"

chmod +x install-dotnet.sh

install-dotnet.ps1:

param([string[]]$Workloads = @())
$ErrorActionPreference = 'Stop'
$installDir = '.dotnet'; $channel = '11.0'; $quality = 'preview'
$version = ''; $rollForward = 'latestFeature'; $allowPrerelease = $true
$errorMessage = 'Required .NET SDK not found. Run ./install-dotnet.sh (or .ps1) to install it locally.'
$installScript = Join-Path $env:TEMP "dotnet-install-$([guid]::NewGuid()).ps1"
try {
    Invoke-WebRequest -Uri 'https://dot.net/v1/dotnet-install.ps1' -OutFile $installScript
    $installArgs = @('-InstallDir', $installDir)
    if ($version) {
        $installArgs += @('-Version', $version)
        $rollForward = 'disable'
    } else {
        $installArgs += @('-Channel', $channel, '-Quality', $quality)
    }
    & $installScript @installArgs
}
finally {
    if (Test-Path -LiteralPath $installScript) {
        Remove-Item -LiteralPath $installScript -Force
    }
}
$sdkVersion = & "$installDir\dotnet.exe" --version
$globalJson = if (Test-Path 'global.json') {
    Copy-Item 'global.json' 'global.json.bak'
    Get-Content -Path 'global.json' -Raw | ConvertFrom-Json
} else {
    [pscustomobject]@{}
}
if (-not $globalJson.PSObject.Properties['sdk']) {
    $globalJson | Add-Member -MemberType NoteProperty -Name 'sdk' -Value ([pscustomobject]@{})
}
$updates = [ordered]@{
    version = $sdkVersion
    allowPrerelease = $allowPrerelease
    rollForward = $rollForward
    paths = @('.dotnet', '$host$')
    errorMessage = $errorMessage
}
foreach ($entry in $updates.GetEnumerator()) {
    $property = $globalJson.sdk.PSObject.Properties[$entry.Key]
    if ($property) {
        $property.Value = $entry.Value
    } else {
        $globalJson.sdk | Add-Member -MemberType NoteProperty -Name $entry.Key -Value $entry.Value
    }
}
$globalJson | ConvertTo-Json -Depth 10 | Set-Content -Path 'global.json' -Encoding UTF8
if (-not (Test-Path .gitignore) -or -not (Select-String -Path .gitignore -Pattern '^\.dotnet/$' -Quiet)) {
    Add-Content -Path .gitignore -Value '.dotnet/'
}
if ($Workloads.Count -gt 0) { & "$installDir\dotnet.exe" workload install @Workloads }
Write-Host "Done. SDK: $sdkVersion"

Commit these scripts to the repo so teammates can run them.

Step 11 — Verify SDK resolution

dotnet --version

Output should match the locally installed version. If not, check: global.json location, paths array contents, host dotnet version ≥ 10.

Step 12 — Summarize and explain cleanup

Tell the user: SDK installed, global.json configured, .dotnet/ gitignored, system install untouched. Cleanup: delete .dotnet/, remove paths/errorMessage from global.json, optionally delete install scripts. Include the final global.json sdk values (or a short snippet) so the user can see the configured version, paths, and any errorMessage. If workloads were requested, include the local dotnet workload install ... command used and the workload verification result or the exact blocker if the workload could not be installed.

Common pitfalls

Pitfall	Cause	Fix
paths ignored	Host dotnet < v10	Install .NET 10+ system-wide
Wrong SDK resolves	global.json in parent directory	Check for global.json up the tree
Teammates get "SDK not found"	.dotnet/ gitignored, no install script run	Use errorMessage in global.json
Workloads missing	Used system dotnet instead of local	Use ./.dotnet/dotnet workload install
dotnet app.dll wrong runtime	paths is SDK-only, not apphost	Use dotnet run or set DOTNET_ROOT