How to Automate Git Workflows and Refactor Legacy Codebases with Claude

gcommit() {
  local diff
  diff=$(git diff --staged)

  if [ -z "$diff" ]; then
    echo "No staged changes."
    return 1
  fi

  local message
  message=$(echo "$diff" | curl -s https://api.anthropic.com/v1/messages \
    -H "x-api-key: $ANTHROPIC_API_KEY" \
    -H "anthropic-version: 2023-06-01" \
    -H "content-type: application/json" \
    -d "$(jq -n --arg diff "$diff" '{
      model: "claude-haiku-4-5-20251001",
      max_tokens: 200,
      messages: [{
        role: "user",
        content: ("Write a concise git commit message for this diff. Use the imperative mood. One line, under 72 characters. No explanation, just the message.\n\n" + $diff)
      }]
    }')" | python3 -c "import sys,json; print(json.load(sys.stdin)['content'][0]['text'])")

  echo "Proposed message: $message"
  echo -n "Commit with this message? [Y/n] "
  read confirm
  if [[ "$confirm" != "n" && "$confirm" != "N" ]]; then
    git commit -m "$message"
  fi
}

gpr-desc() {
  local base=${1:-main}
  local log
  local diff

  log=$(git log "$base"...HEAD --oneline)
  diff=$(git diff "$base"...HEAD -- ':!package-lock.json' ':!*.lock')

  # Truncate diffs larger than 8KB to stay within a reasonable API payload
  if [ ${#diff} -gt 8000 ]; then
    diff="${diff:0:8000}
[diff truncated — showing first 8,000 chars]"
  fi

  curl -s https://api.anthropic.com/v1/messages \
    -H "x-api-key: $ANTHROPIC_API_KEY" \
    -H "anthropic-version: 2023-06-01" \
    -H "content-type: application/json" \
    -d "$(jq -n --arg log "$log" --arg diff "$diff" '{
      model: "claude-sonnet-5-20260101",
      max_tokens: 600,
      messages: [{
        role: "user",
        content: ("Write a pull request description for these changes. Include: a one-sentence summary, what changed and why (2-3 bullets), and what the reviewer should focus on. Be specific about the files and behavior affected.\n\nCommit log:\n" + $log + "\n\nDiff:\n" + $diff)
      }]
    }')" | python3 -c "import sys,json; print(json.load(sys.stdin)['content'][0]['text'])"
}

cat src/payments/processor.ts | claude-ask "Explain what this module does, what its main dependencies are, and what I'd need to understand before modifying it."

cat src/db/queries.ts src/api/routes.ts | claude-ask "Trace the data flow from an incoming HTTP request to a database query in this code."

cat src/auth/session.ts | claude-ask "What are the side effects of the createSession function? What breaks if I change its signature?"

claude "List any functions or exports in src/utils/ that appear to be unused. Check imports across the src/ directory."

git status  # Must be clean before starting
git stash   # If there are unrelated changes

claude "Find every place in src/ that calls the getUserById function. List the files and line numbers."

claude "Update the getUserById calls in src/api/users.ts to use the new findUserById signature: findUserById(id: string, options?: { includeDeleted?: boolean }). Read the file first, then make the minimum change."

npx tsc --noEmit  # TypeScript errors catch most signature mismatches
npm test          # Or whatever your test runner is

import Anthropic from "@anthropic-ai/sdk";
import { execSync } from "child_process";
import fs from "fs/promises";
import { globSync } from "glob";

const client = new Anthropic();

async function runMigration(
  oldName: string,
  newName: string,
  sourceGlob: string
) {
  // Find files that contain the old function name
  const files = globSync(sourceGlob).filter((f) => {
    try {
      return fs.readFile(f, "utf-8").toString().includes(oldName);
    } catch {
      return false;
    }
  });

  console.log(`Found ${files.length} files to update`);

  for (const file of files) {
    console.log(`Processing ${file}...`);

    const messages: Anthropic.MessageParam[] = [
      {
        role: "user",
        content: `In ${file}, replace all calls to ${oldName} with ${newName}. The function signature may be different — check what ${oldName} receives and what ${newName} expects, then adapt the call sites accordingly. Read the file first. Make only the minimum changes needed for this migration.`,
      },
    ];

    // Run the agent on this file
    let done = false;
    let iterations = 0;
    while (!done && iterations++ < 10) {
      const response = await client.messages.create({
        model: "claude-sonnet-5-20260101",
        max_tokens: 4096,
        system: "You are a coding agent performing a migration. Read files before editing. Make minimal changes. After editing, verify the file compiles if possible.",
        tools: [/* read_file, edit_file, run_command tools */],
        messages,
      });

      messages.push({ role: "assistant", content: response.content });

      if (response.stop_reason === "end_turn") {
        done = true;
      } else {
        // ... handle tool calls
      }
    }

    // After each file, check it compiles
    try {
      execSync(`npx tsc --noEmit ${file}`, { stdio: "pipe" });
      console.log(`  ✓ ${file} compiles`);
    } catch (error) {
      console.error(`  ✗ ${file} has compile errors — review manually`);
    }
  }

  // Final check
  try {
    execSync("npx tsc --noEmit", { stdio: "pipe" });
    console.log("\nAll files compile. Migration complete.");
  } catch {
    console.error("\nCompile errors remain. Review the flagged files.");
  }
}

runMigration("getUserById", "findUserById", "src/**/*.ts");

# Review a dependency update
git diff HEAD package-lock.json | head -200 | claude-ask "Summarize what changed in this dependency update and flag anything that might be a breaking change or security concern."

# Understand a teammate's PR before merging
gh pr diff 142 | claude-ask "Explain what this PR changes, why the approach makes sense, and flag anything that looks risky or worth discussing before merging."

# Understand an auto-generated migration
cat migrations/20260831_add_user_roles.sql | claude-ask "Explain what this database migration does, whether it's reversible, and what the application impact will be during deployment."