Batch Scripting

Batch Scripting

Structured protocol for bulk file operations using claude -p. Teaches a safe, resumable pattern — not a framework.

When to Use

• Large-scale transforms (migrate 50+ files from one pattern to another)
• Bulk refactoring (rename across codebase, update imports, convert syntax)
• Batch code generation (add tests, docs, or boilerplate to many files)
• Codebase-wide migrations (CommonJS to ESM, API version bumps, framework upgrades)

Rule of 500 (reach-for-a-script threshold): when a change spans more than ~500 edits — lines to change or repetitive transformations to apply across the codebase — stop hand-editing and reach for this scripted, manifest-driven protocol. (This is a total-edit-volume heuristic, not a file count: this skill's file-count floor is lower, ~50 files per the use cases above, because many files needing one edit each is also batch work.) Below that volume, direct edits are usually faster and safer; above it, the per-edit error rate and context cost of doing it by hand outweigh the setup cost of a manifest + dry-run + log-based retry. The number is a heuristic, not a gate — a smaller but highly repetitive or mechanical change is also a fit.

Protocol

Step 1: Enumerate targets (manifest)

Build the full file list FIRST. Show it to the user. Get explicit approval before proceeding.

# Session-scoped working directory — prevents concurrent session collisions
BATCH_DIR=$(mktemp -d /tmp/agent-batch-XXXXXX)

# Generate manifest — adapt the glob/grep to the specific task
find src -name "*.ts" -not -path "*/node_modules/*" > "$BATCH_DIR/manifest.txt"
echo "Found $(wc -l < "$BATCH_DIR/manifest.txt") files. Review the list:"
cat "$BATCH_DIR/manifest.txt"

Never skip manifest review. The user must see and approve the file list.

Step 2: Dry run (2-3 files)

Process 2-3 representative files first. Show full diffs. Get user approval before the full run.

# Pick representative files (first, middle, last)
head -1 "$BATCH_DIR/manifest.txt" | xargs -I{} claude -p "Transform {} as follows: [PROMPT]. Output ONLY the transformed file content." > "$BATCH_DIR/dry-run-output.txt"
diff /path/to/original "$BATCH_DIR/dry-run-output.txt"

If the dry run does not look right, adjust the prompt and re-run. Do NOT proceed to the full batch with a bad prompt.

Step 3: Execute with logging

Loop over the manifest. Log pass/fail per file. Use atomic writes (write to .tmp, then move).

A zero exit code is not proof of a good transformation — claude -p can exit 0 while writing empty, truncated, or garbage output ("returns 200 and is wrong"). Gate the OK on a cheap per-file postcondition, not on the exit code alone: the output is non-empty and passes a cheap sanity/parse check for the file type (e.g. python -m py_compile, node --check, jq . , yq, or at minimum "still contains an expected structural token"). This is the batch counterpart of project-verification's gate-gaming guard, and it matters most for targets the test suite never exercises (config, docs, generated code) — Step 5's suite cannot catch a silently-mangled YAML file. Unchanged output is not a failure — a file already in the target state is a SKIP (do NOT route it to retry, or an idempotent file loops forever).

while IFS= read -r file; do
  cp "$file" "${file}.bak"
  if claude -p "Transform $file as follows: [PROMPT]. Output ONLY the file content." > "${file}.tmp" 2>/dev/null \
     && [ -s "${file}.tmp" ] \
     && sanity_check "${file}.tmp"; then           # sanity_check: parse/compile/structural probe for this file type
    if cmp -s "${file}.tmp" "${file}.bak"; then
      rm -f "${file}.tmp" "${file}.bak"
      echo "SKIP: $file" >> "$BATCH_DIR/results.log" # already in target state — NOT a failure, not retried
    else
      mv "${file}.tmp" "$file"; rm -f "${file}.bak"
      echo "OK: $file" >> "$BATCH_DIR/results.log"
    fi
  else
    rm -f "${file}.tmp" "${file}.bak"
    echo "FAIL: $file" >> "$BATCH_DIR/results.log"   # empty / unparseable / nonzero exit => FAIL, enters retry; never a silent OK
  fi
done < "$BATCH_DIR/manifest.txt"

Step 4: Handle failures (log-based retry)

After the batch, check the log. Re-run only the failures.

# Check results (SKIP = already in target state; not a failure)
echo "Results:"
echo "  OK:   $(grep -c '^OK:'   "$BATCH_DIR/results.log")"
echo "  SKIP: $(grep -c '^SKIP:' "$BATCH_DIR/results.log")"
echo "  FAIL: $(grep -c '^FAIL:' "$BATCH_DIR/results.log")"

# Retry failures only (SKIP/OK are not retried). Strip the "FAIL: " prefix with sed,
# not cut -d' ' — cut would truncate paths containing spaces.
grep "^FAIL:" "$BATCH_DIR/results.log" | sed 's/^FAIL: //' > "$BATCH_DIR/retry.txt"
# Re-run step 3 with $BATCH_DIR/retry.txt as input

Step 5: Verify

After the full batch completes, run the project's test suite and linter. Review the full git diff.

# Run tests
[project test command]

# Review scope of changes
git diff --stat
git diff  # full diff for review

# Clean up session directory
rm -rf "$BATCH_DIR"

Step 6: Checkpoint for large batches

For 100+ files, process in chunks of 20. Pause between chunks for user confirmation.

split -l 20 "$BATCH_DIR/manifest.txt" "$BATCH_DIR/chunk-"
for chunk in "$BATCH_DIR/chunk-"*; do
  echo "Processing chunk: $chunk ($(wc -l < "$chunk") files)"
  # Run step 3 loop on this chunk
  echo "Chunk complete. Continue? [y/n]"
done

Anti-patterns

• No JSON state files — a text log is sufficient. grep FAIL is your resume mechanism.
• No rate-limit backoff logic — claude -p handles its own rate limiting. If you hit limits, reduce chunk size or wait.
• No rollback infrastructure — git IS your rollback. Run the batch on a branch, review, revert if bad.
• No progress bars — wc -l "$BATCH_DIR/results.log" tells you where you are.
• Never write in-place without .tmp — always write to a temp file, verify, then move.
• Clean up .bak on interrupted runs — the postcondition pattern writes a ${file}.bak before transforming; a run interrupted (Ctrl-C) between the cp and the mv/rm leaves stale .bak files in the tree. They won't re-enter a *.ts-style manifest, but must not be committed — sweep them before re-running and before commit with find . -name '*.bak' -delete. (A per-iteration trap … "${file}.bak" EXIT does NOT work — at EXIT $file holds only the last iteration's value, so other .bak files survive; if you want a trap, scope it to the sweep: trap 'find . -name "*.bak" -delete' EXIT.)

Integration

• Pairs with verification-before-completion after batch completes
• Use a git branch for rollback, not custom undo logic
• For interactive (non-headless) batch work, consider dispatching-parallel-agents instead