Which of the following commands is recommended against for copying a string to a destination buffer without checking its length?

The command recommended against for copying a string to a destination buffer without checking its length is strcpy. This function copies a string from a source to a destination without any bounds checking. If the source string is longer than the destination buffer, strcpy can cause a buffer overflow, leading to potential vulnerabilities such as memory corruption or security breaches.

In contrast, other options like strncpy and snprintf provide mechanisms for limiting the number of characters copied, reducing the risk of buffer overflow. strncpy allows you to specify a maximum number of characters to copy, which helps in managing the size of the destination buffer. snprintf also formats strings with a specified maximum output size, ensuring that the buffer does not overflow.

Using strcat is also not inherently unsafe, but like strcpy, it can lead to buffer overflows if not used carefully, as it appends one string to another without checking if there is enough room in the destination buffer. Therefore, strcpy is the most outright risky choice for copying strings due to its lack of length checks, making it the recommended command to avoid in secure coding practices.