Then you can only specify start and stop position. Curl also supports ftp upload through a proxy, but only if the proxy is configured to allow that kind of tunneling.
If it does, you can run curl in a fashion similar to:. If curl fails where it is not supposed to, if the servers do not let you in, if you cannot understand the responses: use the -v flag to get verbose fetching.
Curl will output lots of info and what it sends and receives in order to let the user see all client-server interaction but it will not show you the actual data.
To get even more details and information on what curl does, try using the --trace or --trace-ascii options with a given file name to log to, like this:. The HTTP information is a lot more extensive. Note that headers stored in a separate file can be useful at a later time if you want curl to use cookies sent by the server. More about that in the cookies section. It's easy to post data using curl. The post data must be urlencoded.
If there's a "normal" post, you use -d to post. The data must be properly URL encoded. This latter type supports things like file upload. If you want the contents to be read from a file, use filename as contents. You can also post the contents of several files in one field. For example, the field name 'coolfiles' is used to send three files, with different content types using the following syntax:.
Emulate a fill-in form with -F. Let's say you fill in three fields in a form. One field is a file name which to post, one field is your name and one field is a file description. We want to post the file we have written named "cooltext. To let curl do the posting of this data instead of your favourite browser, you have to read the HTML source of the form page and find the names of the input fields.
In our example, the input field names are 'file', 'yourname' and 'filedescription'. This is recommended when the value is obtained from a user or some other unpredictable source. Under these circumstances, using -F instead of --form-string could allow a user to trick curl into uploading a file.
An HTTP request has the option to include information about which address referred it to the actual page. Curl allows you to specify the referrer to be used on the command line. It is especially useful to fool or trick stupid servers or CGI scripts that rely on that information being available or contain certain data.
An HTTP request has the option to include information about the browser that generated the request. Curl allows it to be specified on the command line.
It is especially useful to fool or trick stupid servers or CGI scripts that only accept certain browsers. Cookies are generally used by web servers to keep state information at the client's side. Curl also has the ability to use previously received cookies in following sessions. If you get cookies from a server and store them in a file in a manner similar to:.
While saving headers to a file is a working way to store cookies, it is however error-prone and not the preferred way to do this. Instead, make curl save the incoming cookies using the well-known netscape cookie format like this:. Note that by specifying -b you enable the "cookie awareness" and with -L you can make curl follow a location: which often is used in combination with cookies.
So that if a site sends cookies and a location, you can use a non-existing file to trigger the cookie awareness like:. Curl will determine what kind it is based on the file contents. In the above command, curl will parse the header and store the cookies received from www.
The file "empty. To read and write cookies from a netscape cookie file, you can set both -b and -c to use the same file:. The progress meter exists to show a user that something actually is happening. The different fields in the output have the following meaning:. The - option will display a totally different progress bar that does not need much explanation! Curl allows the user to set the transfer speed conditions that must be met to let the transfer keep going.
By using the switch -y and -Y you can make curl abort transfers if the transfer speed is below the specified lowest limit for a specified time. To have curl abort the download if the speed is slower than bytes per second for 1 minute, run:. This can be used in combination with the overall time limit, so that the above operation must be completed in whole within 30 minutes:.
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To demonstrate the usage of the curl program, first, we need a dummy file to download. Any online file will work for this, as long as you have the direct download link. For this guide, I will use the small file provided by think broadband. This is a very basic way of using curl.
We will download the dummy file. With this flag, the file will be downloaded and saved at the current working directory. Need to download multiple files? Follow the command structure shown below. Curl allows you to limit the download speed. Here, the download speed is limited to 1mb. It is also possible to manage an FTP server using curl. Downloading files from an FTP server is like the method shown before.
However, assuming the FTP server requires user authentication, use the following command structure:. In certain situations, the URL that you are trying to access may be blocked due to a lack of a proper user agent.
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