diff-preview

```bash

# Git

git --version

# Gemini for AI explanations

pip install google-generativeai

export GEMINI_API_KEY=your_api_key

```

Basic Diff Commands

```bash

# Working directory changes

git diff

# Staged changes

git diff --staged

git diff --cached

# Specific file

git diff path/to/file.ts

# Between commits

git diff abc123 def456

# Between branches

git diff main feature-branch

git diff main...feature-branch # Since branch diverged

# Show stat summary

git diff --stat

git diff --shortstat

# Name only

git diff --name-only

git diff --name-status # With status (M/A/D)

```

Diff Output Options

```bash

# Word diff (better for prose)

git diff --word-diff

# Color words

git diff --color-words

# Ignore whitespace

git diff -w

git diff --ignore-all-space

# Context lines

git diff -U10 # 10 lines of context (default 3)

# Show function names

git diff --function-context

```

Commit Comparison

```bash

# Last commit

git diff HEAD~1

# Last N commits

git diff HEAD~5

# Specific commit range

git diff abc123..def456

# What changed in a specific commit

git show abc123

```

Explain Changes

```bash

# Get diff and explain

DIFF=$(git diff --staged)

gemini -m pro -o text -e "" "Explain these code changes in plain English:

$DIFF

Summarize:

1. What was changed
2. Why it might have been changed
3. Any potential issues"

```

Impact Analysis

```bash

DIFF=$(git diff main...feature-branch)

gemini -m pro -o text -e "" "Analyze the impact of these changes:

$DIFF

Consider:

1. Breaking changes
2. Performance implications
3. Security considerations
4. Files/systems affected
5. Testing recommendations"

```

Pre-Commit Review

```bash

# Review staged changes before commit

git diff --staged | gemini -m pro -o text -e "" "Review this code diff for:

1. Bugs or issues
2. Code style problems
3. Missing error handling
4. Security concerns

Provide specific line references if issues found."

```

Generate Commit Message

```bash

DIFF=$(git diff --staged)

gemini -m pro -o text -e "" "Based on this diff, suggest a commit message:

$DIFF

Use conventional commit format (feat/fix/chore/etc).

First line under 50 chars, then details."

```

Compare Branches

```bash

# Summary

git diff main feature-branch --stat

# Full diff

git diff main feature-branch

# Since branch point

git diff main...feature-branch

# Commits unique to feature branch

git log main..feature-branch --oneline

```

Find What Changed

```bash

# What files changed between commits

git diff --name-only abc123 def456

# What changed in a file

git log -p -- path/to/file.ts

# When was a line added

git blame path/to/file.ts

```

Merge Preview

```bash

# Preview merge conflicts

git merge --no-commit --no-ff feature-branch

git diff --staged

git merge --abort # Clean up

```

Pre-Commit Check

```bash

#!/bin/bash

# Check staged changes before commit

echo "=== Changes to commit ==="

git diff --staged --stat

echo ""

echo "=== Detailed diff ==="

git diff --staged

echo ""

read -p "Proceed with commit? (y/n) " -n 1 -r

if [[ $REPLY =~ ^[Yy]$ ]]; then

git commit

fi

```

PR Review Prep

```bash

# Get full PR diff for review

BASE=${1:-main}

BRANCH=$(git branch --show-current)

echo "=== Files changed ==="

git diff $BASE...$BRANCH --name-status

echo ""

echo "=== Stats ==="

git diff $BASE...$BRANCH --shortstat

echo ""

echo "=== AI Summary ==="

git diff $BASE...$BRANCH | gemini -m pro -o text -e "" "Summarize this PR's changes for a code reviewer. Focus on the intent and key changes."

```

Track Specific Changes

```bash

# Find all changes to a function

git log -p -S "functionName" -- "*.ts"

# Find changes mentioning something

git log -p --grep="JIRA-123"

```

1. Review before commit - Always check git diff --staged
2. Use stat first - Get overview before full diff
3. Compare with base - Use main...branch for PR context
4. Ignore whitespace - Use -w for meaningful changes
5. Request AI review - For complex changes
6. Save important diffs - Redirect to file for reference