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Git Show and Revision Syntax

git show reads an object or a path from a recorded tree. Revision syntax lets you select a commit relative to a known reference.

How it works

The note changes once, leaving HEAD as the new commit and HEAD~1 as its first parent. A colon separates a revision from a file path when reading tree content. These expressions are precise references, not special filenames on disk. For merge commits, parent selection needs more care because there can be more than one parent.

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

The script creates bhylu-git-show 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 show.ps1 lab

Example

show.ps1

# Bhylu Git lab: Show and Revision Syntax
# 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-show'
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 replacement hinge'
    git add '--' 'notes.md'
    git commit -m 'Record replacement note'
    Assert-Equal (git show HEAD:notes.md) @('Inspect replacement hinge')
    Assert-Equal (git show HEAD~1:notes.md) @('Inspect hinge')
    git show --stat --oneline HEAD
    Write-Output 'Verified: show'
} 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 replacement hinge'
git add '--' 'notes.md'
git commit -m 'Record replacement note'
Assert-Equal (git show HEAD:notes.md) @('Inspect replacement hinge')
Assert-Equal (git show HEAD~1:notes.md) @('Inspect hinge')
git show --stat --oneline HEAD

Expected result

HEAD contains Inspect replacement hinge; its first parent contains Inspect hinge.

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

Reading an older file does not switch branches or replace your working copy. That makes show useful before choosing an undo operation. Quote expressions if your shell treats characters such as braces or carets specially.

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