CURLOPT_DIRLISTONLY man page
CURLOPT_DIRLISTONLY — ask for names only in a directory listing
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DIRLISTONLY, long listonly);
For FTP and SFTP based URLs a parameter set to 1 tells the library to list the names of files in a directory, rather than performing a full directory listing that would normally include file sizes, dates etc.
For POP3 a parameter of 1 tells the library to list the email message or messages on the POP3 server. This can be used to change the default behaviour of libcurl, when combined with a URL that contains a message ID, to perform a "scan listing" which can then be used to determine the size of an email.
Note: For FTP this causes a NLST command to be sent to the FTP server. Beware that some FTP servers list only files in their response to NLST; they might not include subdirectories and symbolic links.
Setting this option to 1 also implies a directory listing even if the URL doesn't end with a slash, which otherwise is necessary.
Do NOT use this option if you also use CURLOPT_WILDCARDMATCH(3) as it will effectively break that feature then.
FTP, SFTP and POP3
This option was known as CURLOPT_FTPLISTONLY up to 7.16.4. POP3 is supported since 7.21.5.
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
curl_easy_setopt(3), CURLOPT_APPEND(3), CURLOPT_FTP_FILEMETHOD(3).