Git Forks and Upstream
A fork is a hosting relationship between repositories. A clone is a local repository copy. A contributor often uses origin for their fork and upstream for the original project.
How it works
The lab models those repository roles using two local bare stores. It adds an upstream remote and fetches its main branch without changing the current working branch. This proves remote naming and fetch behavior, not a GitHub fork object, permission grant or cross-fork pull request. Always follow the original project’s contribution and license rules.
Run the disposable lab
Use Windows PowerShell 5.1 or later and Git 2.28 or later. The reviewed CLI is Git for Windows 2.53.0.windows.2. These are PowerShell examples, not Git Bash commands. Save the download as forks.ps1 in a separate empty learning folder and run it in a separate process: powershell -NoProfile -ExecutionPolicy Bypass -File .\forks.ps1. The execution-policy option applies to that process, not your machine policy.
The script creates bhylu-git-forks and refuses an existing folder. It supplies two fictional seed files and repository-local settings, then runs the lesson commands. The literal separator is quoted as '--' so PowerShell passes it through the guard. A guard function named git calls the real CLI and stops on unexpected failures; Expect-GitFailure checks deliberately refused operations. Child-process configuration isolates your personal Git settings. File transports are allowed only for owned local remotes; internet transports are disabled in this lab. No hosting account, Apache or MySQL service is required. There is no Git playground. Leave the generated folder for inspection; choose another empty parent to run again.
Test boundary: Local remote roles only; no hosted fork is created.
Example
# Bhylu Git lab: Forks and Upstream
# Run in a separate PowerShell process, in an empty learning folder.
# Existing lab folders are refused; nothing is pushed to an internet host.
$ErrorActionPreference = 'Stop'
$script:GitExe = (Get-Command git -CommandType Application | Select-Object -First 1).Source
$script:LabRoot = Join-Path (Get-Location) 'bhylu-git-forks'
if (Test-Path -LiteralPath $script:LabRoot) { throw 'Lab folder already exists. Choose another empty parent folder.' }
New-Item -ItemType Directory -Path $script:LabRoot | Out-Null
$env:GIT_CONFIG_NOSYSTEM = '1'
$env:GIT_CONFIG_GLOBAL = Join-Path $script:LabRoot 'empty-global-config'
[IO.File]::WriteAllText($env:GIT_CONFIG_GLOBAL, '')
$env:GIT_TERMINAL_PROMPT = '0'
$env:GIT_EDITOR = 'true'
$env:GIT_SEQUENCE_EDITOR = 'true'
$env:GIT_AUTHOR_DATE = '2026-01-10T10:00:00+00:00'
$env:GIT_COMMITTER_DATE = $env:GIT_AUTHOR_DATE
function git {
& $script:GitExe -c protocol.allow=never -c protocol.file.allow=always @args
if ($LASTEXITCODE -ne 0) { throw "Git exited with code $LASTEXITCODE" }
}
function Expect-GitFailure {
& $script:GitExe -c protocol.allow=never -c protocol.file.allow=always @args
if ($LASTEXITCODE -eq 0) { throw 'Expected Git to refuse this operation' }
}
function Assert-Equal($Actual, $Expected) {
if ((($Actual | Out-String).Trim()) -cne (($Expected | Out-String).Trim())) { throw "Expected [$Expected], got [$Actual]" }
}
function Write-LabFile([string]$Name, [string]$Text) {
$target = [IO.Path]::GetFullPath((Join-Path (Get-Location) $Name))
if (!$target.StartsWith($script:LabRoot + [IO.Path]::DirectorySeparatorChar, [StringComparison]::OrdinalIgnoreCase)) { throw 'Path outside lab' }
[IO.Directory]::CreateDirectory([IO.Path]::GetDirectoryName($target)) | Out-Null
[IO.File]::WriteAllText($target, ($Text.Replace('\n', "`n") + "`n"), (New-Object Text.UTF8Encoding($false)))
}
function New-LabRepo([string]$Name) {
New-Item -ItemType Directory -Path $Name | Out-Null
Push-Location $Name
try {
git init --initial-branch=main
git config --local user.name 'Repair Lab'
git config --local user.email 'repair@example.invalid'
git config --local core.autocrlf false
git config --local commit.gpgSign false
git config --local tag.gpgSign false
git config --local core.hooksPath (Join-Path $script:LabRoot 'empty-hooks')
Write-LabFile 'notes.md' 'Inspect hinge'
Write-LabFile 'tasks.txt' 'desk=open'
git add '--' notes.md tasks.txt
git commit -m 'Record initial repair plan'
} finally { Pop-Location }
}
Push-Location $script:LabRoot
try {
New-LabRepo 'desk'
Set-Location desk
git init --bare --initial-branch=main ../shared.git
git remote add origin ../shared.git
git push -u origin main
git clone --bare ../shared.git ../upstream.git
git remote add upstream ../upstream.git
git fetch upstream
Assert-Equal (git remote get-url upstream) @('../upstream.git')
Assert-Equal (git rev-parse upstream/main) (git rev-parse main)
Assert-Equal (git branch --show-current) @('main')
Write-Output 'Verified: forks'
} finally { Pop-Location }
Focus on the lesson commands
This excerpt omits the seed repository and guard helpers. Use the complete download to run it.
git init --bare --initial-branch=main ../shared.git
git remote add origin ../shared.git
git push -u origin main
git clone --bare ../shared.git ../upstream.git
git remote add upstream ../upstream.git
git fetch upstream
Assert-Equal (git remote get-url upstream) @('../upstream.git')
Assert-Equal (git rev-parse upstream/main) (git rev-parse main)
Assert-Equal (git branch --show-current) @('main')
Expected result
Two remotes are configured; upstream/main is fetched while the current branch remains main.
The complete script ends with Verified: forks only after its checks pass. Object IDs, temporary paths and progress output can differ.
Remote names are conventions rather than special permission levels. To synchronize a real fork, fetch the intended upstream branch and choose the agreed integration policy before pushing to your fork. A host may restrict visibility, workflow execution or branch updates independently of Git.