如何从Bash脚本检查程序是否存在？

if [ "$(which program_name)" != "" ]; then
  echo "程序存在"
else
  echo "程序不存在"
fi

if command -v program_name >/dev/null 2>&1; then
  echo "程序存在"
else
  echo "程序不存在"
fi

if type program_name >/dev/null 2>&1; then
  echo "程序存在"
else
  echo "程序不存在"
fi