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Git Staging Exercises

Practise selecting one change while leaving another untouched. Predict the committed tree before running the worked solution.

How it works

The brief is to commit an inspection update but keep a closure draft uncommitted. Write both files, stage only the note and inspect the cached diff. The solution checks the task content from HEAD as well as the working file, because a single clean-status assertion would miss the intended leftover draft.

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 exercises.ps1 in a separate empty learning folder and run it in a separate process: powershell -NoProfile -ExecutionPolicy Bypass -File .\exercises.ps1. The execution-policy option applies to that process, not your machine policy.

The script creates bhylu-git-exercises 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.

Download the complete exercises.ps1 lab

Example

exercises.ps1

# Bhylu Git lab: Staging Exercises
# 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-exercises'
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
    Write-LabFile 'notes.md' 'Inspect hinge before handover'
    Write-LabFile 'tasks.txt' 'desk=closed-draft'
    git add '--' notes.md
    Assert-Equal (git diff --cached --name-only) @('notes.md')
    git commit -m 'Clarify handover inspection'
    Assert-Equal (git show HEAD:tasks.txt) @('desk=open')
    Assert-Equal (Get-Content tasks.txt) @('desk=closed-draft')
    Assert-Equal (git show HEAD:notes.md) @('Inspect hinge before handover')
    Write-Output 'Verified: exercises'
} finally { Pop-Location }
Focus on the lesson commands

This excerpt omits the seed repository and guard helpers. Use the complete download to run it.

Lesson excerpt

Write-LabFile 'notes.md' 'Inspect hinge before handover'
Write-LabFile 'tasks.txt' 'desk=closed-draft'
git add '--' notes.md
Assert-Equal (git diff --cached --name-only) @('notes.md')
git commit -m 'Clarify handover inspection'
Assert-Equal (git show HEAD:tasks.txt) @('desk=open')
Assert-Equal (Get-Content tasks.txt) @('desk=closed-draft')
Assert-Equal (git show HEAD:notes.md) @('Inspect hinge before handover')

Expected result

The commit updates notes.md only. HEAD still has desk=open while the working task remains a closure draft.

The complete script ends with Verified: exercises only after its checks pass. Object IDs, temporary paths and progress output can differ.

Try a second exercise: stage the task, edit it again and explain all three versions before committing anything. Use show HEAD:path, show :path and Get-Content to inspect them. Do not replace the exercise with add . unless the brief deliberately includes every changed file.

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