c: Copyright (C) 1998 - 2022, Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Long: form
Short: F
Arg: <name=content>
Help: Specify multipart MIME data
Protocols: HTTP SMTP IMAP
Mutexed: data head upload-file
Category: http upload
Example: --form "name=curl" --form "file=@loadthis" $URL
Added: 5.0
See-also: data form-string form-escape
Multi: append
---
For HTTP protocol family, this lets curl emulate a filled-in form in which a
user has pressed the submit button. This causes curl to POST data using the
Content-Type multipart/form-data according to RFC 2388.

For SMTP and IMAP protocols, this is the means to compose a multipart mail
message to transmit.

This enables uploading of binary files etc. To force the 'content' part to be
a file, prefix the file name with an @ sign. To just get the content part from
a file, prefix the file name with the symbol <. The difference between @ and <
is then that @ makes a file get attached in the post as a file upload, while
the < makes a text field and just get the contents for that text field from a
file.

Tell curl to read content from stdin instead of a file by using - as
filename. This goes for both @ and < constructs. When stdin is used, the
contents is buffered in memory first by curl to determine its size and allow a
possible resend. Defining a part's data from a named non-regular file (such
as a named pipe or similar) is unfortunately not subject to buffering and will
be effectively read at transmission time; since the full size is unknown
before the transfer starts, such data is sent as chunks by HTTP and rejected
by IMAP.

Example: send an image to an HTTP server, where 'profile' is the name of the
form-field to which the file portrait.jpg will be the input:

 curl -F profile=@portrait.jpg https://example.com/upload.cgi

Example: send your name and shoe size in two text fields to the server:

 curl -F name=John -F shoesize=11 https://example.com/

Example: send your essay in a text field to the server. Send it as a plain
text field, but get the contents for it from a local file:

 curl -F "story=<hugefile.txt" https://example.com/

You can also tell curl what Content-Type to use by using 'type=', in a manner
similar to:

 curl -F "web=@index.html;type=text/html" example.com

or

 curl -F "name=daniel;type=text/foo" example.com

You can also explicitly change the name field of a file upload part by setting
filename=, like this:

 curl -F "file=@localfile;filename=nameinpost" example.com

If filename/path contains ',' or ';', it must be quoted by double-quotes like:

 curl -F "file=@\\"local,file\\";filename=\\"name;in;post\\"" example.com

or

 curl -F 'file=@"local,file";filename="name;in;post"' example.com

Note that if a filename/path is quoted by double-quotes, any double-quote
or backslash within the filename must be escaped by backslash.

Quoting must also be applied to non-file data if it contains semicolons,
leading/trailing spaces or leading double quotes:

 curl -F 'colors="red; green; blue";type=text/x-myapp' example.com

You can add custom headers to the field by setting headers=, like

  curl -F "submit=OK;headers=\\"X-submit-type: OK\\"" example.com

or

  curl -F "submit=OK;headers=@headerfile" example.com

The headers= keyword may appear more that once and above notes about quoting
apply. When headers are read from a file, Empty lines and lines starting
with '#' are comments and ignored; each header can be folded by splitting
between two words and starting the continuation line with a space; embedded
carriage-returns and trailing spaces are stripped.
Here is an example of a header file contents:

  # This file contain two headers.
  X-header-1: this is a header

  # The following header is folded.
  X-header-2: this is
   another header

To support sending multipart mail messages, the syntax is extended as follows:
.br
- name can be omitted: the equal sign is the first character of the argument,
.br
- if data starts with '(', this signals to start a new multipart: it can be
followed by a content type specification.
.br
- a multipart can be terminated with a '=)' argument.

Example: the following command sends an SMTP mime email consisting in an
inline part in two alternative formats: plain text and HTML. It attaches a
text file:

 curl -F '=(;type=multipart/alternative' \\
      -F '=plain text message' \\
      -F '= <body>HTML message</body>;type=text/html' \\
      -F '=)' -F '=@textfile.txt' ...  smtp://example.com

Data can be encoded for transfer using encoder=. Available encodings are
*binary* and *8bit* that do nothing else than adding the corresponding
Content-Transfer-Encoding header, *7bit* that only rejects 8-bit characters
with a transfer error, *quoted-printable* and *base64* that encodes data
according to the corresponding schemes, limiting lines length to 76
characters.

Example: send multipart mail with a quoted-printable text message and a
base64 attached file:

 curl -F '=text message;encoder=quoted-printable' \\
      -F '=@localfile;encoder=base64' ... smtp://example.com

See further examples and details in the MANUAL.