Network Working Group Y. Shafranovich
Request for Comments: 4180 SolidMatrix Technologies, Inc.
Category: Informational October 2005
Common Format and MIME Type for Comma-Separated Values (CSV) Files
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This RFC documents the format used for Comma-Separated Values (CSV)
files and registers the associated MIME type "text/csv".
Table of Contents
1. Introduction ....................................................2
2. Definition of the CSV Format ....................................2
3. MIME Type Registration of text/csv ..............................4
4. IANA Considerations .............................................5
5. Security Considerations .........................................5
6. Acknowledgments .................................................6
7. References ......................................................6
7.1. Normative References .......................................6
7.2. Informative References .....................................6
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1. Introduction
The comma separated values format (CSV) has been used for exchanging
and converting data between various spreadsheet programs for quite
some time. Surprisingly, while this format is very common, it has
never been formally documented. Additionally, while the IANA MIME
registration tree includes a registration for
"text/tab-separated-values" type, no MIME types have ever been
registered with IANA for CSV. At the same time, various programs and
operating systems have begun to use different MIME types for this
format. This RFC documents the format of comma separated values
(CSV) files and formally registers the "text/csv" MIME type for CSV
in accordance with RFC 2048 [1].
2. Definition of the CSV Format
While there are various specifications and implementations for the
CSV format (for ex. [4], [5], [6] and [7]), there is no formal
specification in existence, which allows for a wide variety of
interpretations of CSV files. This section documents the format that
seems to be followed by most implementations:
1. Each record is located on a separate line, delimited by a line
break (CRLF). For example:
aaa,bbb,ccc CRLF
zzz,yyy,xxx CRLF
2. The last record in the file may or may not have an ending line
break. For example:
aaa,bbb,ccc CRLF
zzz,yyy,xxx
3. There maybe an optional header line appearing as the first line
of the file with the same format as normal record lines. This
header will contain names corresponding to the fields in the file
and should contain the same number of fields as the records in
the rest of the file (the presence or absence of the header line
should be indicated via the optional "header" parameter of this
MIME type). For example:
field_name,field_name,field_name CRLF
aaa,bbb,ccc CRLF
zzz,yyy,xxx CRLF
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4. Within the header and each record, there may be one or more
fields, separated by commas. Each line should contain the same
number of fields throughout the file. Spaces are considered part
of a field and should not be ignored. The last field in the
record must not be followed by a comma. For example:
aaa,bbb,ccc
5. Each field may or may not be enclosed in double quotes (however
some programs, such as Microsoft Excel, do not use double quotes
at all). If fields are not enclosed with double quotes, then
double quotes may not appear inside the fields. For example:
"aaa","bbb","ccc" CRLF
zzz,yyy,xxx
6. Fields containing line breaks (CRLF), double quotes, and commas
should be enclosed in double-quotes. For example:
"aaa","b CRLF
bb","ccc" CRLF
zzz,yyy,xxx
7. If double-quotes are used to enclose fields, then a double-quote
appearing inside a field must be escaped by preceding it with
another double quote. For example:
"aaa","b""bb","ccc"
The ABNF grammar [2] appears as follows:
file = [header CRLF] record *(CRLF record) [CRLF]
header = name *(COMMA name)
record = field *(COMMA field)
name = field
field = (escaped / non-escaped)
escaped = DQUOTE *(TEXTDATA / COMMA / CR / LF / 2DQUOTE) DQUOTE
non-escaped = *TEXTDATA
COMMA = %x2C
CR = %x0D ;as per section 6.1 of RFC 2234 [2]
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DQUOTE = %x22 ;as per section 6.1 of RFC 2234 [2]
LF = %x0A ;as per section 6.1 of RFC 2234 [2]
CRLF = CR LF ;as per section 6.1 of RFC 2234 [2]
TEXTDATA = %x20-21 / %x23-2B / %x2D-7E
3. MIME Type Registration of text/csv
This section provides the media-type registration application (as per
RFC 2048 [1].
To: ietf-types@iana.org
Subject: Registration of MIME media type text/csv
MIME media type name: text
MIME subtype name: csv
Required parameters: none
Optional parameters: charset, header
Common usage of CSV is US-ASCII, but other character sets defined
by IANA for the "text" tree may be used in conjunction with the
"charset" parameter.
The "header" parameter indicates the presence or absence of the
header line. Valid values are "present" or "absent".
Implementors choosing not to use this parameter must make their
own decisions as to whether the header line is present or absent.
Encoding considerations:
As per section 4.1.1. of RFC 2046 [3], this media type uses CRLF
to denote line breaks. However, implementors should be aware that
some implementations may use other values.
Security considerations:
CSV files contain passive text data that should not pose any
risks. However, it is possible in theory that malicious binary
data may be included in order to exploit potential buffer overruns
in the program processing CSV data. Additionally, private data
may be shared via this format (which of course applies to any text
data).
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Interoperability considerations:
Due to lack of a single specification, there are considerable
differences among implementations. Implementors should "be
conservative in what you do, be liberal in what you accept from
others" (RFC 793 [8]) when processing CSV files. An attempt at a
common definition can be found in Section 2.
Implementations deciding not to use the optional "header"
parameter must make their own decision as to whether the header is
absent or present.
Published specification:
While numerous private specifications exist for various programs
and systems, there is no single "master" specification for this
format. An attempt at a common definition can be found in Section
2.
Applications that use this media type:
Spreadsheet programs and various data conversion utilities
Additional information:
Magic number(s): none
File extension(s): CSV
Macintosh File Type Code(s): TEXT
Person & email address to contact for further information:
Yakov Shafranovich <ietf@shaftek.org>
Intended usage: COMMON
Author/Change controller: IESG
4. IANA Considerations
The IANA has registered the MIME type "text/csv" using the
application provided in Section 3 of this document.
5. Security Considerations
See discussion above in section 3.
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6. Acknowledgments
The author would like to thank Dave Crocker, Martin Duerst, Joel M.
Halpern, Clyde Ingram, Graham Klyne, Bruce Lilly, Chris Lilley, and
members of the IESG for their helpful suggestions. A special word of
thanks goes to Dave for helping with the ABNF grammar.
The author would also like to thank Henrik Lefkowetz, Marshall Rose,
and the folks at xml.resource.org for providing many of the tools
used for preparing RFCs and Internet drafts.
A special thank you goes to L.T.S.
7. References
7.1. Normative References
[1] Freed, N., Klensin, J., and J. Postel, "Multipurpose Internet
Mail Extensions (MIME) Part Four: Registration Procedures", BCP
13, RFC 2048, November 1996.
[2] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[3] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.
7.2. Informative References
[4] Repici, J., "HOW-TO: The Comma Separated Value (CSV) File
Format", 2004,
<http://www.creativyst.com/Doc/Articles/CSV/CSV01.htm>.
[5] Edoceo, Inc., "CSV Standard File Format", 2004,
<http://www.edoceo.com/utilis/csv-file-format.php>.
[6] Rodger, R. and O. Shanaghy, "Documentation for Ricebridge CSV
Manager", February 2005,
<http://www.ricebridge.com/products/csvman/reference.htm>.
[7] Raymond, E., "The Art of Unix Programming, Chapter 5", September
2003,
<http://www.catb.org/~esr/writings/taoup/html/ch05s02.html>.
[8] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
September 1981.
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Author's Address
Yakov Shafranovich
SolidMatrix Technologies, Inc.
EMail: ietf@shaftek.org
URI: http://www.shaftek.org
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RFC 4180 Common Format and MIME Type for CSV Files October 2005
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