Show HN: Block dangerous Git and shell commands from being executed by agents

A developer released a high-performance hook tool called dcg that blocks dangerous Git and shell commands from being executed by AI coding agents, protecting against accidental data loss from commands like git reset --hard or rm -rf. The tool supports multiple agent platforms including Claude Code, Codex CLI, Gemini CLI, and Copilot CLI, and offers zero-config protection with sub-millisecond latency.

A high-performance hook for AI coding agents that blocks destructive commands before they execute, protecting your work from accidental deletion across Claude Code, Codex CLI, Gemini CLI, Copilot CLI, VS Code Copilot Chat, Cursor, Hermes Agent, Grok xAI , and related tools. Supported: Claude Code https://claude.ai/code , Codex CLI 0.125.0+ https://github.com/openai/codex , Gemini CLI https://github.com/google-gemini/gemini-cli , GitHub Copilot CLI https://docs.github.com/en/copilot/concepts/agents/coding-agent/about-hooks , VS Code Copilot Chat https://code.visualstudio.com/docs/agent-customization/hooks , Cursor IDE https://cursor.com , Hermes Agent https://github.com/NousResearch/hermes-agent , Grok xAI https://x.ai/news/grok-build-cli native ~/.grok/hooks/ plus Claude compatibility layer , Antigravity CLI agy https://antigravity.google native ~/.gemini/config/hooks.json via dcg install --agy , OpenCode https://opencode.ai via community plugin https://github.com/aspiers/ai-config/blob/main/.config/opencode/plugins/dcg-guard.js , Pi https://github.com/earendil-works/pi via extension recipe /Dicklesworthstone/destructive command guard/blob/main/docs/pi-integration.md , Aider https://aider.chat/ limited—git hooks only , Continue https://continue.dev detection only curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/install.sh?$ date +%s " | bash -s -- --easy-mode Works on Linux, macOS, and Windows via WSL. Auto-detects your platform, downloads the right binary, and configures supported agent hooks including Claude Code, Codex CLI, Gemini CLI, GitHub Copilot CLI, VS Code Copilot Chat through VS Code's Claude-hook compatibility , Cursor IDE, Hermes Agent, and Grok xAI via dcg install --grok for a native ~/.grok/hooks/dcg.json, or via the Claude compatibility layer automatically picked up by Grok . For native Windows, use the PowerShell installer below. & scriptblock ::Create irm "https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/install.ps1" -EasyMode -Verify Installs native dcg.exe, verifies the SHA256 checksum and the Sigstore/cosign signature when cosign is present , adds it to your User PATH -EasyMode , runs a self-test -Verify , and configures detected agent hooks for Claude Code, Codex CLI, Gemini CLI, GitHub Copilot CLI, Cursor IDE, and Hermes Agent. Copilot is configured at the user level under %COPILOT HOME%\hooks or %USERPROFILE%\.copilot\hooks so every workspace is protected. On Windows the windows.filesystem and windows.system packs are on by default, so del /s, rd /s, Remove-Item -Recurse -Force, format, and vssadmin delete shadows are blocked out of the box. Pin a version with -Version vX.Y.Z. The Problem : AI coding agents Claude, Codex, Gemini, Copilot, etc. occasionally run catastrophic commands like git reset --hard , rm -rf ./src , or DROP TABLE users —destroying hours of uncommitted work in seconds. The Solution : dcg is a high-performance hook that intercepts destructive commands before they execute, blocking them with clear explanations and safer alternatives. | Feature | What It Does | |---|---| Zero-Config Protection | Blocks dangerous git/filesystem commands out of the box | 50+ Security Packs | Databases, Kubernetes, Docker, AWS/GCP/Azure, Terraform, and more | Sub-Millisecond Latency | SIMD-accelerated filtering—you won't notice it's there | Heredoc/Inline Script Scanning | Catches python -c "os.remove ... " and embedded shell scripts | Smart Context Detection | Won't block grep "rm -rf" data but will block rm -rf / execution | Rich Terminal Output | Human-readable denial panels, rule context, and suggestions on stderr | Agent-Safe Streams | Machine-readable hook output stays on stdout while rich UI stays on stderr | Native Codex Support | Codex CLI 0.125.0+ receives a minimal stdout JSON denial that current clients enforce reliably | Graceful Degradation | Plain output for CI, pipes, dumb terminals, and no-color environments | Scan Mode for CI | Pre-commit hooks and CI integration to catch dangerous commands in code review | Fail-Open Design | Never blocks your workflow due to timeouts or parse errors | Explain Mode | dcg explain "command" shows exactly why something is blocked | bash AI agent tries to run: $ git reset --hard HEAD~5 dcg intercepts and blocks: ════════════════════════════════════════════════════════════════ BLOCKED dcg ──────────────────────────────────────────────────────────────── Reason: git reset --hard destroys uncommitted changes Command: git reset --hard HEAD~5 Tip: Consider using 'git stash' first to save your changes. ════════════════════════════════════════════════════════════════ ~/.config/dcg/config.toml packs enabled = "database.postgresql", Blocks DROP TABLE, TRUNCATE "kubernetes.kubectl", Blocks kubectl delete namespace "cloud.aws", Blocks aws ec2 terminate-instances "containers.docker", Blocks docker system prune dcg automatically detects which AI coding agent is invoking it and can apply agent-specific configuration. The trust level field is an advisory label recorded in JSON output and logs — it does not directly change rule evaluation. Behavioral differences come from the other profile fields: | Option | Effect | |---|---| disabled packs | Removes rule packs from evaluation | extra packs | Adds rule packs to evaluation | additional allowlist | Adds command patterns that bypass deny rules | disabled allowlist | When true , ignores all allowlist entries | Trust Claude Code more — wider allowlist, fewer packs agents.claude-code trust level = "high" additional allowlist = "npm run build", "cargo test" disabled packs = "kubernetes" Restrict unknown agents — extra rules, no allowlist bypass agents.unknown trust level = "low" extra packs = "paranoid" disabled allowlist = true See docs/agents.md /Dicklesworthstone/destructive command guard/blob/main/docs/agents.md for full documentation on supported agents, trust levels, and configuration options. dcg now treats Codex CLI as a first-class hook target, not just a Claude-shaped compatibility path. The installer configures Codex CLI 0.125.0+ automatically when it detects codex on PATH or an existing ~/.codex/ directory. | Codex behavior | dcg handling | |---|---| | Hook config | Merges a PreToolUse Bash hook into ~/.codex/hooks.json | | Denied command | Exits 0 with a minimal hookSpecificOutput denial on stdout; human warning stays on stderr | | Allowed command | Exits 0 with empty stdout and stderr | | Existing hooks | Preserves coexisting hooks, keeps dcg first for Bash, and refuses to overwrite malformed JSON | | Validation | Covered by subprocess protocol tests plus an opt-in real Codex E2E harness | Codex's hook input is intentionally close to Claude Code's, but Codex rejects unknown fields in hook output. dcg detects Codex payloads from the non-empty turn id field and emits only Codex's documented denial fields so a blocked command is reported as blocked rather than as a failed hook. See docs/codex-integration.md /Dicklesworthstone/destructive command guard/blob/main/docs/codex-integration.md for protocol details, manual probes, and troubleshooting. This project began as a Python script by Jeffrey Emanuel, who recognized that AI coding agents, while incredibly useful, occasionally run catastrophic commands that destroy hours of uncommitted work. The original implementation was a simple but effective hook that intercepted dangerous git and filesystem commands before execution. - Original concept and Python implementation Jeffrey Emanuel https://github.com/Dicklesworthstone source https://github.com/Dicklesworthstone/misc coding agent tips and scripts/blob/main/DESTRUCTIVE GIT COMMAND CLAUDE HOOKS SETUP.md ; substantially expanded the Rust version with the modular pack system 50+ security packs , heredoc/inline-script scanning, the three-tier architecture, context classification, allowlists, scan mode, and the dual regex engine- Initial Rust port with performance optimizations Darin Gordon https://github.com/Dowwie The initial Rust port by Darin maintained pattern compatibility with the original Python implementation while adding sub-millisecond execution through SIMD-accelerated filtering and lazy-compiled regex patterns. Jeffrey subsequently expanded the Rust codebase dramatically to add the features described above. If dcg is blocking something you genuinely need to run: | Method | Scope | How | |---|---|---| Env var bypass | Single command | DCG BYPASS=1 <command | Allow-once code | Single command | Copy the short code from the block message, run dcg allow-once <code | Permanent allowlist | Rule or command | dcg allowlist add core.git:reset-hard -r "reason" | Remove the hook | All commands | Delete or comment out the dcg entry in ~/.claude/settings.json or equivalent for your agent | DCG BYPASS=1 disables all protection for that invocation. Use it sparingly and prefer allowlists for recurring needs. dcg uses a modular "pack" system to organize destructive command patterns by category. Packs can be enabled or disabled in the configuration file. - Full pack ID index: docs/packs/README.md - Canonical descriptions + pattern counts: dcg packs --verbose With no config file present , dcg enables only the packs that guard against the most catastrophic, unrecoverable mistakes: core.filesystem - Dangerous rm -rf outside temp directories always on; cannot be disabled core.git - Destructive git commands that lose uncommitted work, rewrite history, or destroy stashes always on; cannot be disabled system.disk - mkfs , dd -to-device, fdisk , parted , mdadm , lvm removal, wipefs on by default; opt out with disabled = "system.disk" On Windows , two additional packs are on by default so a fresh install blocks the catastrophic native-Windows operations with no config: windows.filesystem - cmd del /s , rd /s , format <drive : and PowerShell Remove-Item -Recurse -Force and aliases , Clear-Content , Clear-RecycleBin default-on on Windows only ; opt out with disabled = "windows.filesystem" or "windows" windows.system - vssadmin delete shadows / wmic shadowcopy delete Volume Shadow Copy destruction , diskpart , Format-Volume , Clear-Disk , Remove-Partition , cipher /w , bcdedit /delete default-on on Windows only ; opt out with disabled = "windows.system" or "windows" The broader windows.misc reg delete , net user /delete , wsl --unregister , robocopy /MIR and windows.powershell registry/provider deletes, Remove-LocalUser , Disable-ComputerRestore , Remove-VM packs are opt-in on every platform. On Unix the windows. packs are registered but off by default; enable them e.g. to scan committed .ps1 / .cmd scripts in CI via packs enabled = "windows" . Every other pack — including database.postgresql and containers.docker — is opt-in and is not active until a config file enables it. Running dcg init writes a starter ~/.config/dcg/config.toml whose packs enabled list turns on database.postgresql and containers.docker as common examples, but that is a generated starter config, not the no-config default. Enable any pack below by adding it to packs enabled — see Enable More Protection enable-more-protection . storage.s3 - Protects against destructive S3 operations like bucket removal, recursive deletes, and sync --delete. storage.gcs - Protects against destructive GCS operations like bucket removal, object deletion, and recursive deletes. storage.minio - Protects against destructive MinIO Client mc operations like bucket removal, object deletion, and admin operations. storage.azure blob - Protects against destructive Azure Blob Storage operations like container deletion, blob deletion, and azcopy remove. remote.rsync - Protects against destructive rsync operations like --delete and its variants. remote.scp - Protects against destructive SCP operations like overwrites to system paths. remote.ssh - Protects against destructive SSH operations like remote command execution and key management. database.postgresql - Protects against destructive PostgreSQL operations like DROP DATABASE, TRUNCATE, and dropdb. database.mysql - MySQL/MariaDB guard. database.mongodb - Protects against destructive MongoDB operations like dropDatabase, dropCollection, and remove without criteria. database.redis - Protects against destructive Redis operations like FLUSHALL, FLUSHDB, and mass key deletion. database.sqlite - Protects against destructive SQLite operations like DROP TABLE, DELETE without WHERE, and accidental data loss. database.supabase - Protects against destructive Supabase CLI operations including database resets, migration rollbacks, function/secret/storage deletion, project removal, and infrastructure changes. containers.docker - Protects against destructive Docker operations like system prune, volume prune, and force removal. containers.compose - Protects against destructive Docker Compose operations like down -v which removes volumes. containers.podman - Protects against destructive Podman operations like system prune, volume prune, and force removal. kubernetes.kubectl - Protects against destructive kubectl operations like delete namespace, drain, and mass deletion. kubernetes.helm - Protects against destructive Helm operations like uninstall and rollback without dry-run. kubernetes.kustomize - Protects against destructive Kustomize operations when combined with kubectl delete or applied without review. cloud.aws - Protects against destructive AWS CLI operations like terminate-instances, delete-db-instance, and s3 rm --recursive. cloud.azure - Protects against destructive Azure CLI operations like vm delete, storage account delete, and resource group delete. cloud.gcp - Protects against destructive gcloud operations like instances delete, sql instances delete, and gsutil rm -r. cdn.cloudflare workers - Protects against destructive Cloudflare Workers, KV, R2, and D1 operations via the Wrangler CLI. cdn.cloudfront - Protects against destructive AWS CloudFront operations like deleting distributions, cache policies, and functions. cdn.fastly - Protects against destructive Fastly CLI operations like service, domain, backend, and VCL deletion. apigateway.apigee - Protects against destructive Google Apigee CLI and apigeecli operations. apigateway.aws - Protects against destructive AWS API Gateway CLI operations for both REST APIs and HTTP APIs. apigateway.kong - Protects against destructive Kong Gateway CLI, deck CLI, and Admin API operations. infrastructure.ansible - Protects against destructive Ansible operations like dangerous shell commands and unchecked playbook runs. infrastructure.atmos - Protects against destructive Atmos operations like terraform deploy auto-approve , clean, destroy, state rm/taint, and helmfile destroy. infrastructure.pulumi - Protects against destructive Pulumi operations like destroy and up with -y auto-approve . infrastructure.terraform - Protects against destructive Terraform operations like destroy, taint, and apply with -auto-approve. system.disk - Protects against destructive disk operations including dd to devices, mkfs, partition table modifications fdisk/parted , RAID management mdadm , btrfs filesystem operations, device-mapper dmsetup , network block devices nbd-client , and LVM commands pvremove, vgremove, lvremove, lvreduce, pvmove . system.permissions - Protects against dangerous permission changes like chmod 777, recursive chmod/chown on system directories. system.services - Protects against dangerous service operations like stopping critical services and modifying init configuration. cicd.circleci - Protects against destructive CircleCI operations like deleting contexts, removing secrets, deleting orbs/namespaces, or removing pipelines. cicd.github actions - Protects against destructive GitHub Actions operations like deleting secrets/variables or using gh api DELETE against /actions endpoints. cicd.gitlab ci - Protects against destructive GitLab CI/CD operations like deleting variables, removing artifacts, and unregistering runners. cicd.jenkins - Protects against destructive Jenkins CLI/API operations like deleting jobs, nodes, credentials, or build history. secrets.aws secrets - Protects against destructive AWS Secrets Manager and SSM Parameter Store operations like delete-secret and delete-parameter. secrets.doppler - Protects against destructive Doppler CLI operations like deleting secrets, configs, environments, or projects. secrets.onepassword - Protects against destructive 1Password CLI operations like deleting items, documents, users, groups, and vaults. secrets.vault - Protects against destructive Vault CLI operations like deleting secrets, disabling auth/secret engines, revoking leases/tokens, and deleting policies. platform.github - Protects against destructive GitHub CLI operations like deleting repositories, gists, releases, or SSH keys. platform.gitlab - Protects against destructive GitLab platform operations like deleting projects, releases, protected branches, and webhooks. platform.kamal - Protects against destructive Kamal 2.x operations that tear down the stack kamal remove , delete accessory data directories kamal accessory remove , drop proxy routing, take the app offline, or prune the images that kamal rollback relies on. platform.modal - Protects against destructive Modal serverless platform operations like recursive volume removal, app stops with --force , and secret deletion. platform.railway - Protects against destructive Railway CLI and Public API operations that can delete projects, environments, services, functions, volumes, variables, or deployments. dns.cloudflare - Protects against destructive Cloudflare DNS operations like record deletion, zone deletion, and targeted Terraform destroy. dns.generic - Protects against destructive or risky DNS tooling usage nsupdate deletes, zone transfers . dns.route53 - Protects against destructive AWS Route53 DNS operations like hosted zone deletion and record set DELETE changes. email.mailgun - Protects against destructive Mailgun API operations like domain deletion, route deletion, and mailing list removal. email.postmark - Protects against destructive Postmark API operations like server deletion, template deletion, and sender signature removal. email.sendgrid - Protects against destructive SendGrid API operations like template deletion, API key deletion, and domain authentication removal. email.ses - Protects against destructive AWS Simple Email Service operations like identity deletion, template deletion, and configuration set removal. featureflags.flipt - Protects against destructive Flipt CLI and API operations. featureflags.launchdarkly - Protects against destructive LaunchDarkly CLI and API operations. featureflags.split - Protects against destructive Split.io CLI and API operations. featureflags.unleash - Protects against destructive Unleash CLI and API operations. loadbalancer.elb - Protects against destructive AWS Elastic Load Balancing ELB/ALB/NLB operations like deleting load balancers, target groups, or deregistering targets from live traffic. loadbalancer.haproxy - Protects against destructive HAProxy load balancer operations like stopping the service or disabling backends via runtime API. loadbalancer.nginx - Protects against destructive nginx load balancer operations like stopping the service or deleting config files. loadbalancer.traefik - Protects against destructive Traefik load balancer operations like stopping containers, deleting config, or API deletions. messaging.kafka - Protects against destructive Kafka CLI operations like deleting topics, removing consumer groups, resetting offsets, and deleting records. messaging.nats - Protects against destructive NATS/JetStream operations like deleting streams, consumers, key-value entries, objects, and accounts. messaging.rabbitmq - Protects against destructive RabbitMQ operations like deleting queues/exchanges, purging queues, deleting vhosts, and resetting cluster state. messaging.sqs sns - Protects against destructive AWS SQS and SNS operations like deleting queues, purging messages, deleting topics, and removing subscriptions. monitoring.datadog - Protects against destructive Datadog CLI/API operations like deleting monitors and dashboards. monitoring.newrelic - Protects against destructive New Relic CLI/API operations like deleting entities or alerting resources. monitoring.pagerduty - Protects against destructive PagerDuty CLI/API operations like deleting services and schedules which can break incident routing . monitoring.prometheus - Protects against destructive Prometheus/Grafana operations like deleting time series data or dashboards/datasources. monitoring.splunk - Protects against destructive Splunk CLI/API operations like index removal and REST API DELETE calls. payment.braintree - Protects against destructive Braintree/PayPal payment operations like deleting customers or cancelling subscriptions via API/SDK calls. payment.square - Protects against destructive Square CLI/API operations like deleting catalog objects or customers which can break payment flows . payment.stripe - Protects against destructive Stripe CLI/API operations like deleting webhook endpoints and customers, or rotating API keys without coordination. search.algolia - Protects against destructive Algolia operations like deleting indices, clearing objects, removing rules/synonyms, and deleting API keys. search.elasticsearch - Protects against destructive Elasticsearch REST API operations like index deletion, delete-by-query, index close, and cluster setting changes. search.meilisearch - Protects against destructive Meilisearch REST API operations like index deletion, document deletion, delete-batch, and API key removal. search.opensearch - Protects against destructive OpenSearch REST API operations and AWS CLI domain deletions. backup.borg - Protects against destructive borg operations like delete, prune, compact, and recreate. backup.rclone - Protects against destructive rclone operations like sync, delete, purge, dedupe, and move. backup.restic - Protects against destructive restic operations like forgetting snapshots, pruning data, removing keys, and cache cleanup. backup.velero - Protects against destructive velero operations like deleting backups, schedules, and locations. Native-Windows cmd.exe + PowerShell destructive-command protection. windows.filesystem and windows.system are default-on on Windows off/opt-in on Unix ; windows.misc and windows.powershell are opt-in everywhere. All patterns are case-insensitive. windows.filesystem - Recursive/forced filesystem destruction: cmd del /s , rd /s / rmdir /s , format <drive : ; PowerShell Remove-Item -Recurse -Force and aliases rm / del / rd / ri , Clear-Content , Clear-RecycleBin . Whitelists PowerShell -WhatIf previews only on cmdlets/aliases that honor it, plus temp-dir deletes. windows.system - Catastrophic disk/system operations: vssadmin delete shadows and wmic shadowcopy delete Volume Shadow Copy destruction — a ransomware hallmark , diskpart , Format-Volume , Clear-Disk , Remove-Partition , Initialize-Disk / Reset-PhysicalDisk , cipher /w , bcdedit /delete . windows.misc - Registry/account/service/WSL/copy destruction: reg delete , net user|localgroup /delete , sc delete , schtasks /delete , wsl --unregister destroys a WSL distro , robocopy /MIR mirror-delete . windows.powershell - Destructive PowerShell cmdlets: registry/provider deletes Remove-Item HKLM:\ , Remove-ItemProperty , Remove-PSDrive , Remove-LocalUser / Remove-LocalGroup , Unregister-ScheduledTask , Disable-ComputerRestore , forced Stop-Computer / Restart-Computer , Remove-VM / Remove-AppxPackage . package managers - Protects against dangerous package manager operations like publishing packages and removing critical system packages. strict git - Stricter git protections: blocks all force pushes, rebases, and history rewriting operations. Enable packs in ~/.config/dcg/config.toml : packs enabled = Databases "database.postgresql", "database.redis", "database.supabase", Containers and orchestration "containers.docker", "kubernetes", Enables all kubernetes sub-packs Cloud providers "cloud.aws", "cloud.gcp", Secrets management "secrets.aws secrets", "secrets.vault", CI/CD "cicd.jenkins", "cicd.gitlab ci", Messaging "messaging.kafka", "messaging.sqs sns", Search engines "search.elasticsearch", Backup "backup.restic", Platform "platform.github", "platform.railway", Monitoring "monitoring.splunk", Create your own organization-specific security packs using YAML files. Custom packs let you define patterns for internal tools, deployment scripts, and proprietary systems without modifying dcg. packs custom paths = "~/.config/dcg/packs/ .yaml", User packs ".dcg/packs/ .yaml", Project-local packs For detailed pack authoring guide, schema reference, and examples, see docs/custom-packs.md /Dicklesworthstone/destructive command guard/blob/main/docs/custom-packs.md . Validate your pack before deployment: dcg pack validate mypack.yaml Heredoc scanning configuration: heredoc Enable scanning for heredocs and inline scripts python -c, bash -c, etc. . enabled = true Extraction timeout budget milliseconds . timeout ms = 50 Resource limits for extracted bodies. max body bytes = 1048576 max body lines = 10000 max heredocs = 10 Optional language filter scan only these languages . Omit for "all". languages = "python", "bash", "javascript", "typescript", "ruby", "perl", "go" Graceful degradation hook defaults are fail-open . fallback on parse error = true fallback on timeout = true CLI overrides for heredoc scanning: --heredoc-scan / --no-heredoc-scan --heredoc-timeout <ms --heredoc-languages <lang1,lang2,... Heredoc documentation: docs/adr-001-heredoc-scanning.md architecture and rationale docs/patterns.md pattern authoring + inventory docs/security.md threat model and incident response Heredoc and inline script scanning uses a three-tier pipeline designed for performance and accuracy: Command Input │ ▼ ┌─────────────────┐ │ Tier 1: Trigger │ ─── No match ──► ALLOW fast path, <100μs │ RegexSet │ └────────┬────────┘ │ Match ▼ ┌─────────────────┐ │ Tier 2: Extract │ ─── Error/Timeout ──► ALLOW + fallback check │ <1ms │ └────────┬────────┘ │ Success ▼ ┌─────────────────┐ │ Tier 3: AST │ ─── No match ──► ALLOW │ <5ms │ ─── Match ──► BLOCK └─────────────────┘ Tier 1: Trigger Detection <100μs Ultra-fast regex screening to detect heredoc indicators. Uses a compiled RegexSet for O n matching against all trigger patterns simultaneously: static HEREDOC TRIGGERS: LazyLock<RegexSet = LazyLock::new || { RegexSet::new r"<<-?\s ?: '\x22 ^'\x22 '\x22 | \w.- + ", // Heredocs r"<<<", // Here-strings r"\bpython 0-9. \b. \s+- A-Za-z ce ", // python -c/-e r"\bruby 0-9. \b. \s+- A-Za-z e", // ruby -e r"\bnode js ? 0-9. \b. \s+- A-Za-z ep ", // node -e/-p r"\b sh|bash|zsh \b. \s+- A-Za-z c", // bash -c // ... more patterns } ; Commands without any trigger patterns skip directly to ALLOW—no further processing needed. Tier 2: Content Extraction <1ms For commands that trigger, extract the actual content to be evaluated: Heredocs : cat <<EOF ... EOF → extracts body between delimiters Here-strings : cat <<< "content" → extracts quoted content Inline scripts : python -c "code" → extracts the code argument Extraction is bounded by configurable limits: - Maximum body size default: 1MB - Maximum lines default: 10,000 - Maximum heredocs per command default: 10 - Timeout default: 50ms pub struct ExtractionLimits { pub max body bytes: usize, pub max body lines: usize, pub max heredocs: usize, pub timeout ms: u64, } Tier 3: AST Pattern Matching <5ms Extracted content is parsed using language-specific AST grammars via tree-sitter/ast-grep and matched against structural patterns: js // Example: detect subprocess.run with shell=True and rm -rf let pattern = r " call expression { function: attribute { object: "subprocess" attr: "run" } arguments: argument list { contains string { contains "rm -rf" } contains keyword argument { keyword: "shell" value: "True" } } } " ; Recursive Shell Analysis : When extracted content is itself a shell script e.g., bash -c "git reset --hard" , Tier 3 recursively extracts inner commands and re-evaluates them through the full pipeline: js if content.language == ScriptLanguage::Bash { let inner commands = extract shell commands &content.content ; for inner in inner commands { // Re-evaluate inner command against all packs if let Some result = evaluate command &inner, ... { if result.decision == Deny { return result; // Block the outer command } } } } If you encounter commands that should be blocked, please file an issue. Environment variables override config files highest priority : DCG PACKS="containers.docker,kubernetes" : enable packs comma-separated DCG DISABLE="kubernetes.helm" : disable packs/sub-packs comma-separated DCG VERBOSE=0-3 : verbosity level 0 = quiet, 3 = trace DCG QUIET=1 : suppress non-error output DCG COLOR=auto|always|never : color mode DCG NO RICH=1 : disable rich terminal formatting and use plain rendering DCG NO COLOR=1 : disable colored output same as NO COLOR DCG LEGACY OUTPUT=1 : force plain output paths same as --legacy-output DCG ROBOT=1 : enable robot mode for JSON stdout and quiet stderr DCG HIGH CONTRAST=1 : enable high-contrast output ASCII borders + monochrome palette DCG FORMAT=text|json|sarif : default output format command-specific — see Output Formats output-formats-and-dcg format for which values each subcommand actually accepts; real SARIF is dcg scan -only DCG FAIL CLOSED=1 : block deny on hook input that cannot be parsed, instead of the default fail-open allow opt-in; see Fail-Open Philosophy fail-open-philosophy DCG BYPASS=1 : bypass dcg entirely escape hatch; use sparingly DCG CONFIG=/path/to/config.toml : use explicit config file DCG HEREDOC ENABLED=true|false : enable/disable heredoc scanning DCG HEREDOC TIMEOUT=50 : heredoc extraction timeout milliseconds DCG HEREDOC TIMEOUT MS=50 : heredoc extraction timeout milliseconds DCG HEREDOC LANGUAGES=python,bash : filter heredoc languages DCG POLICY DEFAULT MODE=deny|warn|log : global default decision mode DCG HOOK TIMEOUT MS=200 : hook evaluation timeout budget milliseconds --format and the DCG FORMAT env var, which seeds the default is command-specific : each subcommand accepts only its own set of values, and an unrecognized value is a usage error exit 2 . DCG FORMAT applies wherever a command has a --format flag and is silently ignored by commands that don't. | Command | Accepted --format values | Notes | |---|---|---| dcg scan | pretty , json , markdown , sarif | Only command that emits real SARIF 2.1.0 | dcg test | pretty alias text , json aliases sarif , structured , toon | | dcg config | pretty alias text , json alias sarif | | dcg packs | pretty alias text , json alias sarif | | dcg explain | pretty , json alias sarif | | dcg doctor | pretty , json alias sarif | | dcg simulate | pretty , json alias sarif | | dcg corpus | json , pretty alias sarif | | dcg suggest-allowlist | text , json alias sarif | sarif is a JSON alias on every command except dcg scan. This is deliberate so that setting DCG FORMAT=sarif globally degrades gracefully — dcg scan produces a real SARIF report while other commands fall back to their structured JSON rather than erroring. If you need machine-readable output from a non-scan command, prefer --format json which is unambiguous ; use dcg scan --format sarif for SARIF. --robot forces JSON regardless of --format .dcg supports layered configuration from multiple sources, with higher-priority sources overriding lower ones: - Environment Variables DCG prefix HIGHEST PRIORITY - Explicit Config File DCG CONFIG env var - Project Config .dcg.toml in repo root - User Config ~/.config/dcg/config.toml - System Config /etc/dcg/config.toml - Compiled Defaults LOWEST PRIORITY dcg supports colorblind-safe palettes and high-contrast output. Colors are always paired with symbols/labels to avoid conveying meaning by color alone. output high contrast = true ASCII borders + black/white palette theme palette = "colorblind" default | colorblind | high-contrast use unicode = true false for ASCII-only use color = true false for monochrome Configuration File Locations : | Level | Path | Use Case | |---|---|---| | System | /etc/dcg/config.toml | Organization-wide defaults | | User | ~/.config/dcg/config.toml | Personal preferences | | Project | .dcg.toml repo root | Project-specific settings | | Explicit | DCG CONFIG=/path/to/file | Testing or override | Merging Behavior : Configuration layers are merged additively, with higher-priority sources overriding specific fields: // Only fields explicitly set in higher-priority configs override // Missing fields retain values from lower-priority sources fn merge layer &mut self, other: ConfigLayer { if let Some verbose = other.general.verbose { self.general.verbose = verbose; // Override if present } // Unset fields retain previous values } This means you can set organization defaults in /etc/dcg/config.toml , personal preferences in ~/.config/dcg/config.toml , and project-specific overrides in .dcg.toml —each layer only needs to specify the settings that differ from defaults. Project-Specific Pack Configuration : The projects section allows different pack configurations for different repositories: projects."/home/user/work/production-api" packs = { enabled = "database.postgresql", "cloud.aws" , disabled = } projects."/home/user/personal/experiments" packs = { enabled = , disabled = "core.git" } More permissive for experiments dcg is designed with a fail-open philosophy: when the tool cannot safely analyze a command due to timeouts, parse errors, or resource limits , it allows the command to proceed rather than blocking it and breaking the user's workflow. Why Fail-Open? Workflow Continuity : A blocked legitimate command is more disruptive than a missed dangerous one Performance Guarantees : The hook must never become a bottleneck Graceful Degradation : Partial analysis is better than no analysis Fail-Open Scenarios : | Scenario | Behavior | Rationale | |---|---|---| | Parse error in heredoc | ALLOW + warn | Malformed input shouldn't block work | | Extraction timeout | ALLOW + warn | Slow inputs shouldn't hang terminal | | Size limit exceeded | ALLOW + fallback check | Large inputs get reduced analysis | | Regex engine timeout | ALLOW + warn | Pathological patterns shouldn't block | | AST matching error | Skip that heredoc | Continue evaluating other content | | Deadline exceeded | ALLOW immediately | Hard cap prevents runaway processing | Configurable Strictness : For high-security environments, fail-open can be disabled. For heredoc/inline-script analysis specifically: heredoc fallback on parse error = false Block on heredoc parse errors fallback on timeout = false Block on heredoc timeouts For the top-level hook input the JSON dcg reads from stdin , enable fail-closed mode so that input which cannot be parsed at all is blocked instead of allowed: general fail closed = true Deny when the hook input itself is unparseable or at runtime: js DCG FAIL CLOSED=1 env var overrides the config value The default is fail-open unparseable input is allowed and is unchanged unless you opt in. With fail-closed enabled, a genuinely unparseable hook payload produces a deny a permissionDecision: deny for Claude-style hooks; a "decision":"deny" line plus a non-zero exit for dcg hook --batch . Transient IO read errors still fail open even in this mode, since they are not attacker-controlled malformed payloads. A leading UTF-8 BOM EF BB BF is stripped before parsing in all hook paths, so a BOM-prefixed but otherwise-valid command is correctly evaluated and blocked if dangerous rather than allowed through as "unparseable". With strict mode enabled, dcg will block commands when analysis fails, providing detailed error messages explaining why. Fallback Pattern Checking : Even when full analysis is skipped, dcg performs a lightweight fallback check for critical destructive patterns: static FALLBACK PATTERNS: LazyLock<RegexSet = LazyLock::new || { RegexSet::new r"shutil\.rmtree", r"os\.remove", r"fs\.rmSync", r"\brm\s+- a-zA-Z r a-zA-Z f", r"\bgit\s+reset\s+--hard\b", // ... other critical patterns } ; This ensures that even oversized or malformed inputs are checked for the most dangerous operations before being allowed. Absolute Timeout : To prevent any single command from blocking indefinitely, dcg enforces an absolute maximum processing time of 200ms . Any command exceeding this threshold is immediately allowed with a warning logged. The easiest way to install is using the install script, which downloads a prebuilt binary for your platform: curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/install.sh?$ date +%s " | bash -s -- --easy-mode Easy mode auto-detects your platform, downloads the right binary, verifies SHA256 checksums, configures all supported AI agent hooks Claude Code, Codex CLI, Gemini CLI, GitHub Copilot CLI, Cursor IDE, Hermes Agent, Aider , and updates your PATH. For Codex CLI 0.125.0+, the installer merges a PreToolUse Bash hook into ~/.codex/hooks.json ; invalid JSON or malformed existing Codex hook shapes are left unchanged and reported instead of being overwritten. Other options: Interactive mode prompts for each step : curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/install.sh?$ date +%s " | bash Install specific version: curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/install.sh?$ date +%s " | bash -s -- --version v0.5.0 Install to /usr/local/bin system-wide, requires sudo : curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/install.sh?$ date +%s " | sudo bash -s -- --system Build from source instead of downloading binary: curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/install.sh?$ date +%s " | bash -s -- --from-source Download/install only skip agent hook configuration : curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/install.sh?$ date +%s " | bash -s -- --no-configure Note:If you have gum installed, the installer will use it for fancy terminal formatting. The installer also verifies Sigstore cosign bundles when available falls back to checksum-only , falls back to building from source if no prebuilt is available, and removes the legacy Python predecessor git safety guard.py if present. Agent-specific notes Aider: No PreToolUse-style interception. The installer enables git-commit-verify: true in ~/.aider.conf.yml so git hooks run. For full protection, install dcg as a git pre-commit hook /Dicklesworthstone/destructive command guard/blob/main/docs/scan-precommit-guide.md . Continue: No shell command interception hooks. The installer detects Continue but cannot auto-configure protection. Use a git pre-commit hook /Dicklesworthstone/destructive command guard/blob/main/docs/scan-precommit-guide.md instead. Codex CLI: PreToolUse hooks via ~/.codex/hooks.json stable in Codex 0.125.0+; the codex hooks feature is on by default . dcg detects Codex from the turn id stdin field and emits the minimal documented hookSpecificOutput deny JSON with exit code 0; dcg-only metadata is omitted so Codex's strict parser accepts the decision. The Unix installer and install.ps1 both merge dcg's hook into the existing hooks object, detect an already-current dcg hook exactly, leave invalid JSON or malformed hook shapes untouched, and surface the failure reason in the install summary. After installation, open Codex's /hooks UI once to trust the hook. uninstall.sh and uninstall.ps1 remove only dcg-owned Codex hooks and preserve coexisting entries. See the Codex integration notes /Dicklesworthstone/destructive command guard/blob/main/docs/codex-integration.md . Caveats: the model can still write scripts to disk to bypass hook-based blocking; and Codex's PreToolUse hooks do not yet intercept every /Dicklesworthstone/destructive command guard/blob/main/docs/codex-integration.md known-limitation-codex-unified exec-path-windows-desktop--cli , so treat it as a guardrail rather than a complete enforcement boundary. unified exec shell path GitHub Copilot CLI: The installer writes a user-level hook to ${COPILOT HOME:-~/.copilot}/hooks/dcg.json , protecting every workspace. The generated preToolUse hook covers both Unix bash and Windows powershell payloads and emits Copilot's exact top-level permission-decision JSON. VS Code Copilot Chat: Current VS Code releases load ~/.claude/settings.json by default, so the Claude Code hook installed by dcg also protects Copilot Chat without a second bridge or duplicate hook. dcg recognizes VS Code's documented runTerminalCommand shell tool plus the observed compatibility names run in terminal and runInTerminal , reads tool input.command , and returns VS Code's documented hookSpecificOutput deny. Agent hooks are still a VS Code preview feature and can be disabled by organization policy; use Developer: Show Agent Debug Logs or the GitHub Copilot Chat Hooks output channel to confirm that the hook loaded. Cursor IDE: Hooks are configured through ~/.cursor/hooks.json plus a generated bridge dcg-pre-shell.ps1 on Windows . The installer inserts dcg first in beforeShellExecution , collapses duplicate dcg entries, and preserves coexisting Cursor hooks. Hermes Agent: NousResearch's Hermes Agent https://github.com/NousResearch/hermes-agent declares shell hooks in ~/.hermes/config.yaml under hooks.pre tool call . The installer merges a single matcher: "terminal" entry that invokes dcg directly — no wrapper script — because Hermes' input JSON hook event name: "pre tool call" , tool name: "terminal" , tool input.command deserializes straight into dcg's existing HookInput . Hermes explicitly documents https://github.com/NousResearch/hermes-agent/blob/main/website/docs/user-guide/features/hooks.md that "non-zero exit codes... never abort the agent loop", so dcg switches to Hermes' JSON block protocol on output: {"decision":"block","reason":...} plus the alternate {"action":"block","message":...} form for cross-version compatibility . The installer also sets hooks auto accept: true if not already set; Hermes silently drops un-allowlisted hooks in non-TTY runs gateway/cron without it. unconfigure hermes in uninstall.sh removes only the dcg-owned entry and leaves hooks auto accept alone other Hermes hooks may rely on it . Grok xAI : Grok Build / Grok CLI https://x.ai/news/grok-build-cli auto-discovers every .json under ~/.grok/hooks/ . dcg install --grok writes a self-contained ~/.grok/hooks/dcg.json with a PreToolUse / matcher: "Bash" entry — Grok internally aliases Claude-style "Bash" to its own run terminal cmd tool, so a single rule covers every shell command. dcg detects Grok at runtime from the camelCase wire shape hookEventName: "pre tool use" , toolName: "run terminal cmd" or from the GROK SESSION ID / GROK HOOK EVENT / GROK WORKSPACE ROOT environment variables, and switches its output to Grok's JSON contract: {"decision":"deny","reason":...} note "deny" , not Hermes' "block" . Grok also picks up dcg automatically through its ~/.claude/settings.json compatibility layer, so existing Claude Code users get protection with no additional install step. Add --project to write <repo /.grok/hooks/dcg.json for a per-repo install Grok requires /hooks-trust the first time it opens a repo with hooks . Antigravity CLI agy : Google Antigravity's https://antigravity.google ships a Claude-Code-compatible hooks system. agy CLI dcg install --agy merges a PreToolUse / matcher: "Bash" entry into ~/.gemini/config/hooks.json the canonical path; agy migrates the legacy ~/.gemini/antigravity-cli/hooks.json here and symlinks the old path to it . agy runs the hook before its run command shell tool; dcg detects agy at runtime from the distinctive nested toolCall envelope {"toolCall":{"name":"run command","args":{"CommandLine":"…"}},"conversationId":…,"stepIdx":…} — the shell command is read from toolCall.args.CommandLine — or from the ANTIGRAVITY CONVERSATION ID environment variable / agy parent-process name. dcg switches its output to agy 's JSON contract: {"decision":"block","reason":…} with exit code 0 verified: agy honors both "block" and "deny" and aborts the tool; a non-zero exit code is only logged and does NOT reliably block, so dcg always emits exit 0 + JSON . Add --project to write <repo /.gemini/config/hooks.json for a per-repo install. Restart agy start a new session after installing. OpenCode: Not auto-configured. Requires a Bun-based plugin with "tool.execute.before" hook key. A working community plugin: aspiers/ai-config/dcg-guard.js https://github.com/aspiers/ai-config/blob/main/.config/opencode/plugins/dcg-guard.js . Pi: Not auto-configured. Pi https://github.com/earendil-works/pi intercepts shell commands through user-authored TypeScript extensions pi.on "tool call", … , auto-loaded from ~/.pi/agent/extensions/ .ts or <repo /.pi/extensions/ .ts . A ready-to-use dcg-guard.ts extension that routes each bash command through dcg --robot test exit 1 = deny and blocks with the dcg reason is documented in docs/pi-integration.md /Dicklesworthstone/destructive command guard/blob/main/docs/pi-integration.md . Recommended:After installing, run dcg setup to add a shell startup check that warns you if the dcg hook is ever silently removed from ~/.claude/settings.json . This project uses Rust Edition 2024 features and requires the nightly toolchain. The repository includes a rust-toolchain.toml that automatically selects the correct toolchain. Install Rust nightly if you don't have it rustup install nightly Install directly from GitHub cargo +nightly install --git https://github.com/Dicklesworthstone/destructive command guard destructive command guard git clone https://github.com/Dicklesworthstone/destructive command guard cd destructive command guard rust-toolchain.toml automatically selects nightly cargo build --release cp target/release/dcg ~/.local/bin/ Run the built-in updater to re-run the installer for your platform: dcg update Optional flags mirror the installer scripts examples : dcg update --version v0.2.7 dcg update --system dcg update --verify You can always re-run install.sh / install.ps1 directly if preferred. Prebuilt binaries are available for: - Linux x86 64 x86 64-unknown-linux-gnu - Linux ARM64 aarch64-unknown-linux-gnu - macOS Intel x86 64-apple-darwin - macOS Apple Silicon aarch64-apple-darwin - Windows x64 x86 64-pc-windows-msvc - Windows ARM64 aarch64-pc-windows-msvc Download from GitHub Releases https://github.com/Dicklesworthstone/destructive command guard/releases and verify the SHA256 checksum. If you have cosign installed, each release also includes a Sigstore bundle .sigstore.json so you can verify provenance with cosign verify-blob . Remove dcg and all its hooks from AI agents: curl -fsSL https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/uninstall.sh | bash On Windows: irm https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/uninstall.ps1 | iex The Unix uninstaller: - Removes dcg hooks from Claude Code, Codex CLI, Cursor IDE, Gemini CLI, GitHub Copilot CLI user-level plus legacy repo-local , Hermes Agent, and Aider - Removes the dcg binary - Removes configuration ~/.config/dcg/ and history ~/.local/share/dcg/ - Prompts for confirmation before making changes The PowerShell uninstaller removes the Windows dcg.exe binary, the exact User PATH entry added by install.ps1 , dcg hooks from Claude Code, Codex CLI, Gemini CLI, GitHub Copilot CLI, Cursor IDE, Hermes Agent, Grok, and Antigravity agy , plus dcg configuration/history directories. Options: --yes - Skip confirmation prompt --keep-config - Preserve configuration files --keep-history - Preserve history database --purge - Remove everything overrides keep flags Add to ~/.claude/settings.json : { "hooks": { "PreToolUse": { "matcher": "Bash", "hooks": { "type": "command", "command": "dcg" } } } } Important: Restart Claude Code after adding the hook configuration. Codex CLI 0.125.0+ supports stable PreToolUse hooks. The installer writes or merges this automatically, but the manual configuration lives at ~/.codex/hooks.json : { "hooks": { "PreToolUse": { "matcher": "Bash", "hooks": { "type": "command", "command": "dcg" } } } } Codex denials intentionally omit dcg's extended Claude-only fields: dcg exits 0 with the minimal documented hookSpecificOutput JSON on stdout. Allowed commands stay silent with exit code 0. Add to ~/.gemini/settings.json : { "hooks": { "BeforeTool": { "matcher": "run shell command", "hooks": { "name": "dcg", "type": "command", "command": "dcg", "timeout": 5000 } } } } Important: Restart Gemini CLI after adding the hook configuration. While primarily designed as a hook, the binary supports direct invocation for testing, debugging, and understanding why commands are blocked or allowed. Show version with build metadata dcg --version Show help with blocked command categories dcg --help Test a command manually pipe JSON to stdin echo '{"tool name":"Bash","tool input":{"command":"git reset --hard"}}' | dcg Use dcg test to evaluate a command without executing it . This is useful for CI checks, false-positive debugging, and config validation before rollout. Basic evaluation human-readable output dcg test "rm -rf ./build" Structured output for automation dcg test --format json "kubectl delete namespace prod" | jq -r .decision Use a specific config file dcg test --config .dcg.prod.toml "docker system prune" Temporarily enable extra packs only for this test run dcg test --with-packs containers.docker,database.postgresql "docker system prune" Print full evaluation trace same engine as dcg explain dcg test --explain "git reset --hard" 0 : command would be allowed 1 : command would be blocked -c, --config <PATH : use a specific config file --with-packs <ID1,ID2 : temporarily enable extra packs --explain : print detailed decision trace -f, --format <pretty|json|toon : output format default: pretty --no-color : disable ANSI color output --heredoc-scan : force-enable heredoc/inline-script scanning --no-heredoc-scan : force-disable heredoc/inline-script scanning --heredoc-timeout <MS : override heredoc extraction timeout budget --heredoc-languages <LANG1,LANG2 : limit heredoc AST scanning languages pretty : human-readable output with command context, matched rule info, and suggestions json : structured payload for scripts/CI; includes metadata like schema version , dcg version , command , decision , rule/pack fields, and allowlist/agent context when present toon : token-efficient structured encoding of the same payload used by json useful for agent-to-agent/tool pipelines Fail fast in shell pipelines: dcg test --format json "rm -rf /" /tmp/dcg.json jq -e '.decision == "allow"' /tmp/dcg.json Minimal GitHub Actions step: - name: Validate dangerous command policy run: | ~/.local/bin/dcg test --format json "git reset --hard HEAD~1" /tmp/dcg-test.json jq -e '.decision == "allow"' /tmp/dcg-test.json - Use --format json or DCG FORMAT=json for machine parsing. - Add --no-color if logs or parsers choke on ANSI output. - If results differ between environments, check config precedence DCG CONFIG , project .dcg.toml , user/system config . - If a command is unexpectedly allowed, inspect active allowlists dcg allowlist list and enabled packs dcg packs --verbose . - For full decision traces, run dcg test --explain "<command " or dcg explain "<command " . When you need to understand exactly why a command was blocked or allowed , the dcg explain command provides a detailed trace of the decision-making process: Explain why a command is blocked dcg explain "git reset --hard HEAD" Explain a safe command dcg explain "git status" Explain with verbose timing information dcg explain --verbose "rm -rf /tmp/build" Output as JSON for programmatic use dcg explain --format json "kubectl delete namespace production" JSON output is versioned via schema version currently 2 . v2 adds matched span , matched text preview , and explanation in the match object when a pattern is detected. Example Output : Command: git reset --hard HEAD Normalized: git reset --hard HEAD Decision: BLOCKED Pack: core.git Rule: reset-hard Reason: git reset --hard destroys uncommitted changes Evaluation Trace: 0.8μs Quick reject: passed contains 'git' 2.1μs Normalize: no changes 5.3μs Safe patterns: no match checked 34 patterns 12.7μs Destructive patterns: MATCH at pattern 'reset-hard' 12.9μs Total time: 12.9μs Suggestion: Consider using 'git stash' first to save your changes. The explain mode shows: Normalized command : How dcg sees the command after path normalization Decision : Whether the command would be blocked or allowed Matching rule : Which pack and pattern triggered the decision Evaluation trace : Step-by-step timing of each evaluation stage Suggestion : Actionable guidance for safer alternatives This is invaluable for debugging false positives, understanding pack coverage, and verifying that custom allowlist entries work as expected. Sometimes you need to run a blocked command temporarily without permanently modifying your allowlist. The allow-once system provides short codes: When a command is blocked, dcg outputs a short code BLOCKED: git reset --hard HEAD Allow-once code: 123456 To allow this: dcg allow-once 123456 Use the short code to create a temporary exception dcg allow-once 123456 Or, use --single-use to make the exception one-shot dcg allow-once 123456 --single-use How Allow-Once Works : - When dcg blocks a command, it generates a short code currently 6 numeric digits; collisions are handled via --pick / --hash - The code is tied to the exact command that was blocked - Running dcg allow-once <code creates a temporary exception - The exception is stored in ~/.config/dcg/pending exceptions.jsonl - Exceptions expire after 24 hours or after first use if --single-use is used - While active, the exception allows the same command in the same directory scope This workflow is useful for: - One-time administrative operations that are intentionally destructive - Migration scripts that need to reset state - Emergency fixes where permanent allowlist changes aren't appropriate Security Considerations : - Short codes are derived from SHA256 or optional HMAC-SHA256 when DCG ALLOW ONCE SECRET is set - Codes are never logged or transmitted - The pending exceptions file is readable only by the current user - Expired codes are automatically cleaned up AI coding agents routinely get stuck when git pull --rebase fails partway — unstaged-changes errors, stash-pop conflicts, interrupted rebases. The documented recovery path is almost always git checkout -- . or git restore <paths , both of which dcg hard-blocks core.git:checkout-discard , core.git:restore-worktree . Agents then have to stop and ask a human to run the command manually. Rebase-recovery mode is a narrow, bounded relaxation of those two rules that only fires under a genuine recovery signal. Outside that signal the default block is unchanged. Two complementary signals unlock recovery: - Active rebase state automatic, zero-config . When .git/rebase-merge/ or .git/rebase-apply/ exists, a rebase is in progress and the discard operations are the documented recovery path. dcg detects this state and converts the deny into an allow with a dcg Allowing ... → rebase-recovery mode note on stderr. No permit needed. - Explicit permit cookie opt-in, short-lived . When the rebase already finished but the worktree is still messy e.g. after a bad git stash pop , run: dcg rebase-recover default ttl: 120s dcg rebase-recover --ttl 60 custom ttl max: 600s This writes a timestamp to .dcg/rebase-recovery-permit at the repo root. For the next N seconds or until the first matching allow, whichever comes first , git checkout -- <path and git restore <paths are allowed. The permit is single-shot — one successful allow consumes it — so it can't silently unblock later unrelated commands within the TTL. Scope and safety guarantees: - Only four rules participate: core.git:checkout-discard , core.git:checkout-ref-discard , core.git:restore-worktree , core.git:restore-worktree-explicit . Nothing else is affected. git reset --hard , git clean -f , git push --force , etc. stay blocked even during an active rebase or with a permit active.- The permit is scoped to the current repo's .dcg/ directory. It does not cross repos. - Expired permits are auto-cleaned on the next check. Typical recovery flow: bash $ git pull --rebase ... fails with "unstaged changes" ... $ git stash $ git pull --rebase succeeds $ git stash pop leaves messy worktree $ git checkout -- . BLOCKED by dcg core.git:checkout-discard ... Recovering from a failed git pull --rebase ? ... Run dcg rebase-recover in this repo, then retry the command. $ dcg rebase-recover dcg rebase-recovery permit issued ... $ git checkout -- . now allowed, permit consumed $ git push See issue 104 https://github.com/Dicklesworthstone/destructive command guard/issues/104 for background. The --version output includes build metadata for debugging: dcg 0.1.0 Built: 2026-01-07T22:13:10.413872881Z Rustc: 1.94.0-nightly Target: x86 64-unknown-linux-gnu This metadata is embedded at compile time via vergen https://github.com/rustyhorde/vergen , making it easy to identify exactly which build is running when troubleshooting. While the hook protects interactive command execution, teams also need protection against destructive commands that get committed into repositories . The dcg scan command extracts executable command contexts from files and evaluates them using the same pattern engine. What it is: - An extractor-based scanner that understands executable contexts - Uses the same evaluator as hook mode for consistency - Supports CI integration and pre-commit hooks What it is NOT: - A naive grep that matches strings everywhere - A replacement for code review - A static analysis tool for arbitrary languages The key difference from grep: dcg scan understands that "rm -rf /" in a comment is data, not code. It uses extractors that understand file structure shell scripts, Dockerfiles, CI workflows, package scripts, Makefiles, Terraform, Docker Compose to find only actually-executed commands. dcg scan includes specialized extractors for each file format, understanding which parts contain executable commands: | File Type | Detection | Executable Contexts | |---|---|---| Shell Scripts | .sh , .bash , .zsh , .dash , .ksh | Non-comment executable command lines | Dockerfile | Dockerfile , Dockerfile. , .dockerfile | RUN instructions shell and exec forms | GitHub Actions | .github/workflows/ .yml , .github/workflows/ .yaml | run: fields in steps | GitLab CI | .gitlab-ci.yml , .gitlab-ci.yml | script: , before script: , after script: | Azure Pipelines | azure-pipelines.yml , azure-pipelines.yaml , azure-pipelines- .yml , azure-pipelines- .yaml | script: , bash: , powershell: , pwsh: tasks | CircleCI | .circleci/config.yml , .circleci/config.yaml | run: steps and nested command: fields | Makefile | Makefile | Tab-indented recipe lines | package.json | package.json | scripts object values | Terraform | .tf | provisioner blocks local-exec , remote-exec | Docker Compose | docker-compose.yml , docker-compose.yaml , compose.yml , compose.yaml | command: , entrypoint: , healthcheck.test: fields | PowerShell | .ps1 , .psm1 , .psd1 | Executable statements with line and block comments excluded | Batch Scripts | .cmd , .bat | Executable command lines with comments excluded | Context-Aware Extraction : Each extractor understands its format's semantics: GitHub Actions - only 'run:' is extracted - name: Build run: | ← Extracted npm install npm run build env: NODE ENV: production ← Skipped not executable Dockerfile - only RUN instructions FROM node:18 COPY . /app ← Skipped RUN npm install ← Extracted RUN "node", "server.js" ← Extracted exec form ENV PORT=3000 ← Skipped Makefile - tab-indented lines under targets build: npm install ← Extracted recipe line npm run build ← Extracted SOURCES = $ wildcard .js ← Skipped variable assignment Non-Executable Context Filtering : Extractors intelligently skip data-only sections: Shell : Assignment-only lines export VAR=value YAML : environment: , labels: , volumes: , variables: blocks Terraform : Everything outside provisioner blocks All formats : Comments format-appropriate: , // , etc. Install the pre-commit hook dcg scan install-pre-commit Or manually run on staged files dcg scan --staged Scan specific paths dcg scan --paths scripts/ .github/workflows/ Start conservative to avoid developer friction: Week 1-2: Warn-first with narrow scope dcg scan --staged --fail-on error Only fail on catastrophic rules Create .dcg/hooks.toml with conservative defaults: scan fail on = "error" Only fail on high-confidence catastrophic rules format = "pretty" Human-readable output redact = "quoted" Hide sensitive strings truncate = 120 Shorten long commands scan.paths include = ".github/workflows/ ", Start with CI configs "Dockerfile", Container builds "Makefile", Build scripts exclude = "target/ ", "node modules/ ", "vendor/ ", Gradual expansion: Week 1-2 : Start with workflows/Dockerfiles only, --fail-on error Week 3-4 : Add Makefiles and shell scripts in scripts/ Month 2 : Add --fail-on warning after reviewing findings Ongoing : Add new extractors as team confidence grows dcg scan install-pre-commit This creates a .git/hooks/pre-commit that runs dcg scan --staged . If you prefer manual control or use a hook manager: bash /bin/bash .git/hooks/pre-commit or equivalent for your hook manager set -e Run dcg scan on staged files dcg scan --staged --fail-on error Add other hooks below... dcg scan uninstall-pre-commit This only removes hooks installed by dcg detected via sentinel comment . The output includes: scripts/deploy.sh:42:5: ERROR core.git:reset-hard Command: git reset --hard HEAD Reason: git reset --hard destroys uncommitted changes Suggestion: Consider using 'git stash' first to save changes. File:Line:Col : Location in the source file Severity : ERROR catastrophic or WARNING concerning Rule ID : Stable identifier like core.git:reset-hard Command : The extracted command may be redacted/truncated Reason : Why this command is flagged Suggestion : How to make it safer Replace the dangerous command with a safer alternative: Instead of: git reset --hard Use: git stash push -m "before reset" git reset --hard Get detailed analysis: dcg explain "git reset --hard HEAD" If the command is genuinely needed: Project-level allowlist committed, code-reviewed dcg allowlist add core.git:reset-hard --reason "Required for CI cleanup" --project Or for a specific command dcg allowlist add-command "rm -rf ./build" --reason "Build cleanup" --project The finding output includes a copy-paste allowlist command for convenience. Heredoc rules use stable IDs like heredoc.python.shutil rmtree . Scan supports redaction of potentially sensitive content in output. Use --redact quoted to hide quoted strings that may contain secrets: Original command: curl -H "Authorization: Bearer $TOKEN" https://api.example.com With --redact quoted: curl -H "..." https://api.example.com Options: --redact none : Show full commands default --redact quoted : Hide quoted strings recommended for CI logs --redact aggressive : Hide more potential secrets .dcg/hooks.toml project-level, committed : scan Exit non-zero when findings meet this threshold fail on = "error" Options: none, warning, error Output format format = "pretty" Options: pretty, json, markdown Maximum file size to scan bytes max file size = 1000000 Stop after this many findings max findings = 50 Redaction level for sensitive content redact = "quoted" Options: none, quoted, aggressive Truncate long commands chars; 0 = no truncation truncate = 120 scan.paths Only scan files matching these patterns include = "scripts/ ", ".github/workflows/ ", "Dockerfile ", "Makefile", Skip files matching these patterns exclude = "target/ ", "node modules/ ", " .md", CLI flags override config file values. name: Security Scan on: pull request jobs: scan: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 with: fetch-depth: 0 - name: Install dcg run: | curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/install.sh" | bash echo "$HOME/.local/bin" $GITHUB PATH - name: Scan changed files run: | dcg scan --git-diff origin/${{ github.base ref }}..HEAD \ --format markdown \ --fail-on error scan: stage: test script: - curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive command guard/main/install.sh" | bash - ~/.local/bin/dcg scan --git-diff origin/$CI MERGE REQUEST TARGET BRANCH NAME..HEAD --fail-on error rules: - if: $CI MERGE REQUEST ID If you need to bypass the pre-commit hook temporarily: git commit --no-verify -m "Emergency fix" This is logged and visible in git history. For permanent exceptions, use allowlists instead. Your AI agent invokes dcg as a PreToolUse hook before executing each shell command. The hook receives the command as JSON on stdin and runs through a four-stage pipeline: JSON Parsing -- Validates the hook payload Claude/Gemini/Copilot variants , extracts the command string. Non-shell tools are immediately allowed. Normalization -- Strips absolute paths /usr/bin/git becomes git while preserving arguments. Quick Reject -- O n substring search for keywords like "git" or "rm". Commands without these substrings skip regex matching entirely handles 99%+ of non-destructive commands . Pattern Matching -- Safe patterns checked first match = allow . Destructive patterns checked second match = deny with explanation . No match on either = allow. If blocked under a Claude-compatible JSON hook protocol, dcg outputs a JSON denial on stdout and a colorful human-readable warning on stderr. If blocked under Codex CLI, dcg follows Codex's strict hook contract with minimal stdout JSON and exit code 0. If allowed, dcg exits silently. Rich formatting is automatically disabled for CI, non-TTY output, dumb terminals, and no-color environments. ┌─────────────────────────────────────────────────────────────────┐ │ Claude / Codex / Gemini / Copilot / Cursor / Hermes hooks │ │ │ │ User: "delete the build artifacts" │ │ Agent: executes rm -rf ./build │ │ │ └─────────────────────┬───────────────────────────────────────────┘ │ ▼ PreToolUse hook stdin: JSON ┌─────────────────────────────────────────────────────────────────┐ │ dcg │ │ │ │ ┌──────────────┐ ┌──────────────┐ ┌──────────────┐ │ │ │ Parse │───▶│ Normalize │───▶│ Quick Reject │ │ │ │ JSON │ │ Command │ │ Filter │ │ │ └──────────────┘ └──────────────┘ └──────┬───────┘ │ │ │ │ │ ┌───────────────────────────┘ │ │ ▼ │ │ ┌──────────────────────────────────────────────────────────┐ │ │ │ Pattern Matching │ │ │ │ │ │ │ │ 1. Check SAFE PATTERNS whitelist ──▶ Allow if match │ │ │ │ 2. Check DESTRUCTIVE PATTERNS ──────▶ Deny if match │ │ │ │ 3. No match ────────────────────────▶ Allow default │ │ │ │ │ │ │ └──────────────────────────────────────────────────────────┘ │ │ │ └─────────────────────┬───────────────────────────────────────────┘ │ ▼ stdout: JSON deny / empty allow stderr: rich human output / Codex deny reason ┌─────────────────────────────────────────────────────────────────┐ │ Claude / Codex / Gemini / Copilot / Cursor / Hermes hooks │ │ │ │ If denied: Shows block message, does NOT execute command │ │ If allowed: Proceeds with command execution │ │ │ └─────────────────────────────────────────────────────────────────┘ Not every occurrence of a dangerous pattern is actually dangerous. The string git reset --hard appearing in a comment, a heredoc body, or a quoted string is fundamentally different from the same string appearing as an executed command. dcg uses a sophisticated context classification system to reduce false positives without compromising safety. SpanKind Classification Every token in a command is classified into one of these categories: | SpanKind | Description | Treatment | |---|---|---| Executed | Command words and unquoted arguments | MUST check - highest priority | InlineCode | Content inside -c / -e flags bash -c, python -c | MUST check - code will be executed | Argument | Quoted arguments to known-safe commands | Lower priority, context-dependent | Data | Single-quoted strings shell cannot interpolate | Can skip - treated as literal data | HeredocBody | Content inside heredocs | Escalated to Tier 2/3 heredoc scanning | Comment | Shell comments ... | Skip - never executed | Unknown | Cannot determine context | Conservative treatment as Executed | Why Context Matters Consider these commands: Safe: the dangerous pattern is in a comment echo "Reminder: never run git reset --hard" git reset --hard destroys changes Safe: the dangerous pattern is data being searched for grep "git reset --hard" documentation.md Safe: the dangerous pattern is in a heredoc being written to a file cat <<EOF safety guide.md Warning: git reset --hard destroys uncommitted changes EOF DANGEROUS: the pattern will be executed git reset --hard HEAD DANGEROUS: the pattern is passed to bash -c for execution bash -c "git reset --hard" Without context classification, the first three examples would trigger false positives. The context classifier analyzes the AST abstract syntax tree structure to understand where patterns appear and only flags genuinely dangerous occurrences. Implementation Details The context classifier uses a multi-pass approach: Lexical Analysis : Identify quoted strings, comments, and heredoc markers Structural Analysis : Build a tree of command structure, identifying pipes, subshells, and command substitutions Flag Analysis : Detect -c , -e , and similar flags that introduce inline code contexts Span Annotation : Tag each character range with its SpanKind This approach achieves a significant reduction in false positives while maintaining the zero-false-negatives philosophy for actual command execution. Safe patterns are checked before destructive patterns. This design ensures that explicitly safe commands like git checkout -b are never accidentally blocked, even if they partially match a destructive pattern like git checkout . git checkout -b feature → Matches SAFE "checkout-new-branch" → ALLOW git checkout -- file.txt → No safe match, matches DESTRUCTIVE → DENY The hook uses a default-allow policy for unrecognized commands. This ensures: - The hook never breaks legitimate workflows - Only known dangerous patterns are blocked - New git commands are allowed until explicitly categorized The pattern set prioritizes never allowing dangerous commands over avoiding false positives. A few extra prompts for manual confirmation are acceptable; lost work is not. This hook is one layer of protection. It complements not replaces : - Regular commits and pushes - Git stash before risky operations - Proper backup strategies - Code review processes Every Bash command passes through this hook. Performance is critical: - Lazy-initialized static regex patterns compiled once, reused - Quick rejection filter eliminates 99%+ of commands before regex - No heap allocations on the hot path for safe commands - Sub-millisecond execution for typical commands The safe pattern list contains 34 patterns covering: | Category | Patterns | Purpose | |---|---|---| | Branch creation | checkout -b , checkout --orphan | Creating branches is safe | | Staged-only | restore --staged , restore -S | Unstaging doesn't touch working tree | | Dry run | clean -n , clean --dry-run | Preview mode, no actual deletion | | Temp cleanup | rm -rf /tmp/ , rm -rf /var/tmp/ | Ephemeral directories are safe | | Variable expansion | rm -rf $TMPDIR/ , rm -rf ${TMPDIR}/ | Shell variable forms | | Quoted paths | rm -rf "$TMPDIR/ " | Quoted variable forms | | Separate flags | rm -r -f /tmp/ , rm -r -f $TMPDIR/ | Flag ordering variants | | Long flags | rm --recursive --force /tmp/ , $TMPDIR/ | GNU-style long options | The destructive pattern list contains 16 patterns covering: | Category | Pattern | Reason | |---|---|---| | Work destruction | reset --hard , reset --merge | Destroys uncommitted changes | | File reversion | checkout -- <path | Discards file modifications | | Worktree restore | restore without --staged | Discards uncommitted changes | | Untracked deletion | clean -f | Permanently removes untracked files | | History rewrite | push --force , push -f | Can destroy remote commits | | Unsafe branch delete | branch -D | Force-deletes without merge check | | Stash destruction | stash drop , stash clear | Permanently deletes stashed work | | Filesystem nuke | rm -rf non-temp paths | Recursive deletion outside temp | Patterns use fancy-regex https://github.com/fancy-regex/fancy-regex for advanced features: // Negative lookahead: block restore UNLESS --staged is present r"git\s+restore\s+ ? --staged\b ? -S\b " // Negative lookahead: don't match --force-with-lease r"git\s+push\s+. --force ? -a-z " // Character class: match any flag ordering r"rm\s+- a-zA-Z rR a-zA-Z f a-zA-Z "