Claude Code in Scripts: Headless Mode and Automation (2026)

# Interactive (default)
claude
 
# Headless — print result and exit
claude -p "What does this function do?"

# One-shot prompt
claude -p "Generate a TypeScript interface for a blog post with id, title, content, author, and publishedAt"

# Review a file
cat src/lib/auth.ts | claude -p "Review this code for security issues. Be specific about line numbers."
 
# Review multiple files at once
cat src/lib/actions/user.ts src/types/user.ts | claude -p "Are these types consistent with each other?"

claude -p "$(cat <<EOF
Review this TypeScript file for potential issues:
 
$(cat src/services/OrderService.ts)
EOF
)"

# Plain text — no markdown symbols
claude -p "List 3 improvements for this code" --output-format text < src/lib/payments.ts
 
# JSON — structured output for piping
claude -p "Analyze this for security issues. Return JSON with shape:
{ \"issues\": [{ \"line\": number, \"severity\": \"low|medium|high\", \"description\": string }] }" \
  --output-format json < src/lib/auth.ts

claude -p "Analyze and return JSON: { issues: [{severity, description, line}] }" \
  --output-format json < src/lib/auth.ts \
  | jq '.issues[] | select(.severity == "high")'

#!/bin/bash
# scripts/generate-changelog.sh
 
SINCE=${1:-"1 week ago"}
COMMITS=$(git log --oneline --since="$SINCE")
 
if [ -z "$COMMITS" ]; then
  echo "No commits since $SINCE"
  exit 0
fi
 
CHANGELOG=$(claude -p "$(cat <<EOF
Generate a changelog entry in markdown for these git commits.
Group by: Features, Bug Fixes, Improvements, Other.
Use bullet points. Be concise and developer-friendly.
 
Commits:
$COMMITS
EOF
)" --output-format text)
 
# Prepend to CHANGELOG.md
echo "## $(date +%Y-%m-%d)" > /tmp/new-entry.md
echo "" >> /tmp/new-entry.md
echo "$CHANGELOG" >> /tmp/new-entry.md
echo "" >> /tmp/new-entry.md
cat /tmp/new-entry.md CHANGELOG.md > /tmp/full.md
mv /tmp/full.md CHANGELOG.md
 
echo "Changelog updated."

./scripts/generate-changelog.sh              # since 1 week ago
./scripts/generate-changelog.sh "1 day ago"  # since yesterday

#!/bin/bash
# scripts/commit-msg-gen.sh
# Usage: git diff --staged | ./scripts/commit-msg-gen.sh
 
DIFF=$(cat)
 
if [ -z "$DIFF" ]; then
  echo "No staged changes. Run: git diff --staged | ./scripts/commit-msg-gen.sh"
  exit 1
fi
 
claude -p "$(cat <<EOF
Generate a conventional commit message for this diff.
Format: <type>(<scope>): <description>
Types: feat, fix, refactor, docs, test, chore, perf
Keep description under 72 characters.
Add a short body only if the change is complex.
Output the commit message only — no explanation.
 
Diff:
$DIFF
EOF
)" --output-format text

# Preview the suggestion
git diff --staged | ./scripts/commit-msg-gen.sh
 
# Use it directly
git commit -m "$(git diff --staged | ./scripts/commit-msg-gen.sh)"

#!/bin/bash
# scripts/pr-review.sh
 
BASE=${1:-"main"}
FILES=$(git diff --name-only "$BASE"...HEAD)
 
if [ -z "$FILES" ]; then
  echo "No changed files compared to $BASE"
  exit 0
fi
 
echo "# PR Review Report — $(date)" > pr-review.md
echo "" >> pr-review.md
 
for file in $FILES; do
  case "$file" in
    *.md|*.json|*.lock|*.svg|*.png) continue ;;
  esac
 
  [ ! -f "$file" ] && continue
 
  echo "Reviewing $file..."
 
  REVIEW=$(cat "$file" | claude -p "$(cat <<EOF
Review this file for:
1. Potential bugs or edge cases
2. Security issues
3. Missing error handling
4. Performance concerns
 
Be specific — include line numbers where relevant.
If nothing to flag, say "Looks good."
File: $file
EOF
)" --output-format text)
 
  echo "## $file" >> pr-review.md
  echo "" >> pr-review.md
  echo "$REVIEW" >> pr-review.md
  echo "" >> pr-review.md
done
 
echo "Done → pr-review.md"

# .git/hooks/prepare-commit-msg
#!/bin/bash
 
COMMIT_MSG_FILE=$1
COMMIT_SOURCE=$2
 
# Only run when no message is pre-populated
if [ "$COMMIT_SOURCE" = "" ]; then
  STAGED=$(git diff --staged)
  if [ -n "$STAGED" ]; then
    SUGGESTION=$(echo "$STAGED" | claude -p \
      "Write a conventional commit message for this diff. One line, under 72 chars." \
      --output-format text 2>/dev/null)
    if [ -n "$SUGGESTION" ]; then
      echo "# Suggested: $SUGGESTION" > /tmp/msg-suggestion
      cat "$COMMIT_MSG_FILE" >> /tmp/msg-suggestion
      mv /tmp/msg-suggestion "$COMMIT_MSG_FILE"
    fi
  fi
fi

chmod +x .git/hooks/prepare-commit-msg

# .github/workflows/claude-review.yml
name: Claude Code Review
 
on:
  pull_request:
    types: [opened, synchronize]
 
jobs:
  review:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0
 
      - name: Install Claude Code
        run: npm install -g @anthropic-ai/claude-code
 
      - name: Review changed files
        env:
          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
        run: |
          FILES=$(git diff --name-only origin/main...HEAD)
          for file in $FILES; do
            case "$file" in
              *.ts|*.tsx|*.js|*.jsx)
                echo "=== $file ===" >> review.txt
                cat "$file" | claude -p \
                  "Flag any security issues or bugs. Be specific." \
                  --output-format text \
                  --dangerously-skip-permissions \
                  >> review.txt
                echo "" >> review.txt
                ;;
            esac
          done
          cat review.txt

RESULT=$(cat src/main.ts | claude -p "Analyze this code" --output-format text)
STATUS=$?
 
if [ $STATUS -ne 0 ]; then
  echo "Claude Code failed (exit $STATUS)" >&2
  exit 1
fi
 
echo "$RESULT"

run_claude() {
  local input="$1"
  local prompt="$2"
  local retries=3
  local wait=5
 
  for i in $(seq 1 $retries); do
    RESULT=$(echo "$input" | claude -p "$prompt" --output-format text 2>&1)
    [ $? -eq 0 ] && { echo "$RESULT"; return 0; }
    echo "Attempt $i failed, retrying in ${wait}s..." >&2
    sleep $wait
    wait=$((wait * 2))
  done
 
  echo "All $retries attempts failed" >&2
  return 1
}