Hook to enforce native tool

enforce_native_tools.sh

#!/bin/bash
set -euo pipefail

# Read input from stdin
input=$(cat)

# Extract command (jq required)
command -v jq >/dev/null 2>&1 || exit 0
cmd=$(echo "$input" | jq -r '.tool_input.command // empty')
[ -z "$cmd" ] && exit 0

# Strip leading whitespace
cmd="${cmd#"${cmd%%[![:space:]]*}"}"

# Extract first command segment (before any pipe, &&, ||, or ;)
first_segment="${cmd%%|*}"
first_segment="${first_segment%%&&*}"
first_segment="${first_segment%%||*}"
first_segment="${first_segment%%;*}"

# Strip leading env var assignments (e.g., FOO=bar cmd)
clean="$first_segment"
while [[ "$clean" =~ ^[[:space:]]*[A-Za-z_][A-Za-z0-9_]*= ]]; do
  clean="${clean#*[[:space:]]}"
done
clean="${clean#"${clean%%[![:space:]]*}"}"

# Get binary name (first word, strip path)
binary="${clean%% *}"
binary="${binary##*/}"
[ -z "$binary" ] && exit 0

# Unwrap bash -c / sh -c wrappers
if [[ "$binary" == "bash" || "$binary" == "sh" || "$binary" == "zsh" ]]; then
  if [[ "$clean" =~ -c ]]; then
    inner=$(echo "$clean" | sed -E "s/^[^ ]+ +-c +['\"]?//" | sed -E "s/['\"]?\s*$//")
    inner_first="${inner%%|*}"
    inner_first="${inner_first%%&&*}"
    binary="${inner_first%% *}"
    binary="${binary##*/}"
    [ -z "$binary" ] && exit 0
  else
    exit 0
  fi
fi

# Block and redirect to native tools
deny() {
  echo "{\"hookSpecificOutput\": {\"permissionDecision\": \"deny\"}, \"systemMessage\": \"$1\"}" >&2
  exit 2
}

case "$binary" in
  cat)
    deny "Use the Read tool instead of 'cat'. It supports offset and limit parameters for partial file reads." ;;
  head)
    deny "Use the Read tool with the 'limit' parameter instead of 'head'." ;;
  tail)
    deny "Use the Read tool with 'offset' and 'limit' parameters instead of 'tail'." ;;
  grep|rg)
    deny "Use the Grep tool instead of '$binary'. It supports regex, glob filters, context lines (-A/-B/-C), and output modes." ;;
  find)
    deny "Use the Glob tool instead of 'find'. Use patterns like '**/*.ts' for recursive matching." ;;
  ls)
    deny "Use the Glob tool instead of 'ls'. Use patterns like 'src/*' or '**/*.py'." ;;
  sed)
    deny "Use the Edit tool for file modifications instead of 'sed'. Use Read with offset/limit for line extraction." ;;
  awk)
    deny "Use the Grep tool for pattern matching or Edit tool for transformations instead of 'awk'." ;;
  *)
    exit 0 ;;
esac