Class

This class provides a complete interface to CSV files and data. It offers tools to enable you to read and write to and from Strings or IO objects, as needed.

Reading

From a File

A Line at a Time

CSV.foreach("path/to/file.csv") do |row|
  # use row here...
end

All at Once

arr_of_arrs = CSV.read("path/to/file.csv")

From a String

A Line at a Time

CSV.parse("CSV,data,String") do |row|
  # use row here...
end

All at Once

arr_of_arrs = CSV.parse("CSV,data,String")

Writing

To a File

CSV.open("path/to/file.csv", "wb") do |csv|
  csv << ["row", "of", "CSV", "data"]
  csv << ["another", "row"]
  # ...
end

To a String

csv_string = CSV.generate do |csv|
  csv << ["row", "of", "CSV", "data"]
  csv << ["another", "row"]
  # ...
end

Convert a Single Line

csv_string = ["CSV", "data"].to_csv   # to CSV
csv_array  = "CSV,String".parse_csv   # from CSV

Shortcut Interface

CSV             { |csv_out| csv_out << %w{my data here} }  # to $stdout
CSV(csv = "")   { |csv_str| csv_str << %w{my data here} }  # to a String
CSV($stderr)    { |csv_err| csv_err << %w{my data here} }  # to $stderr
CSV($stdin)     { |csv_in|  csv_in.each { |row| p row } }  # from $stdin

Advanced Usage

Wrap an IO Object

csv = CSV.new(io, options)
# ... read (with gets() or each()) from and write (with <<) to csv here ...

CSV and Character Encodings (M17n or Multilingualization)

This new CSV parser is m17n savvy. The parser works in the Encoding of the IO or String object being read from or written to. Your data is never transcoded (unless you ask Ruby to transcode it for you) and will literally be parsed in the Encoding it is in. Thus CSV will return Arrays or Rows of Strings in the Encoding of your data. This is accomplished by transcoding the parser itself into your Encoding.

Some transcoding must take place, of course, to accomplish this multiencoding support. For example, :col_sep, :row_sep, and :quote_char must be transcoded to match your data. Hopefully this makes the entire process feel transparent, since CSV's defaults should just magically work for your data. However, you can set these values manually in the target Encoding to avoid the translation.

It's also important to note that while all of CSV's core parser is now Encoding agnostic, some features are not. For example, the built-in converters will try to transcode data to UTF-8 before making conversions. Again, you can provide custom converters that are aware of your Encodings to avoid this translation. It's just too hard for me to support native conversions in all of Ruby's Encodings.

Anyway, the practical side of this is simple: make sure IO and String objects passed into CSV have the proper Encoding set and everything should just work. CSV methods that allow you to open IO objects (CSV::foreach(), CSV::open(), CSV::read(), and CSV::readlines()) do allow you to specify the Encoding.

One minor exception comes when generating CSV into a String with an Encoding that is not ASCII compatible. There's no existing data for CSV to use to prepare itself and thus you will probably need to manually specify the desired Encoding for most of those cases. It will try to guess using the fields in a row of output though, when using CSV::generate_line() or Array#to_csv().

I try to point out any other Encoding issues in the documentation of methods as they come up.

This has been tested to the best of my ability with all non-“dummy” Encodings Ruby ships with. However, it is brave new code and may have some bugs. Please feel free to report any issues you find with it.


Constants


The encoding used by all converters.

This Hash holds the built-in converters of CSV that can be accessed by name. You can select Converters with CSV.convert() or through the options Hash passed to CSV::new().

:integer

Converts any field Integer() accepts.

:float

Converts any field Float() accepts.

:numeric

A combination of :integer and :float.

:date

Converts any field Date::parse() accepts.

:date_time

Converts any field DateTime::parse() accepts.

:all

All built-in converters. A combination of :date_time and :numeric.

All built-in converters transcode field data to UTF-8 before attempting a conversion. If your data cannot be transcoded to UTF-8 the conversion will fail and the field will remain unchanged.

This Hash is intentionally left unfrozen and users should feel free to add values to it that can be accessed by all CSV objects.

To add a combo field, the value should be an Array of names. Combo fields can be nested with other combo fields.

The options used when no overrides are given by calling code. They are:

:col_sep

","

:row_sep

:auto

:quote_char

'"'

:field_size_limit

nil

:converters

nil

:unconverted_fields

nil

:headers

false

:return_headers

false

:header_converters

nil

:skip_blanks

false

:force_quotes

false

:skip_lines

nil

:liberal_parsing

false

A Regexp used to find and convert some common Date formats.

A Regexp used to find and convert some common DateTime formats.

A FieldInfo Struct contains details about a field's position in the data source it was read from. CSV will pass this Struct to some blocks that make decisions based on field structure. See CSV.convert_fields() for an example.

index

The zero-based index of the field in its row.

line

The line of the data source this row is from.

header

The header for the column, when available.

This Hash holds the built-in header converters of CSV that can be accessed by name. You can select HeaderConverters with CSV.header_convert() or through the options Hash passed to CSV::new().

:downcase

Calls downcase() on the header String.

:symbol

Leading/trailing spaces are dropped, string is downcased, remaining spaces are replaced with underscores, non-word characters are dropped, and finally to_sym() is called.

All built-in header converters transcode header data to UTF-8 before attempting a conversion. If your data cannot be transcoded to UTF-8 the conversion will fail and the header will remain unchanged.

This Hash is intentionally left unfrozen and users should feel free to add values to it that can be accessed by all CSV objects.

To add a combo field, the value should be an Array of names. Combo fields can be nested with other combo fields.

The version of the installed library.

Class Methods


This method is a convenience for building Unix-like filters for CSV data. Each row is yielded to the provided block which can alter it as needed. After the block returns, the row is appended to output altered or not.

The input and output arguments can be anything CSV::new() accepts (generally String or IO objects). If not given, they default to ARGF and $stdout.

The options parameter is also filtered down to CSV::new() after some clever key parsing. Any key beginning with :in_ or :input_ will have that leading identifier stripped and will only be used in the options Hash for the input object. Keys starting with :out_ or :output_ affect only output. All other keys are assigned to both objects.

The :output_row_sep option defaults to $INPUT_RECORD_SEPARATOR ($/).

This method is intended as the primary interface for reading CSV files. You pass a path and any options you wish to set for the read. Each row of file will be passed to the provided block in turn.

The options parameter can be anything CSV::new() understands. This method also understands an additional :encoding parameter that you can use to specify the Encoding of the data in the file to be read. You must provide this unless your data is in Encoding::default_external(). CSV will use this to determine how to parse the data. You may provide a second Encoding to have the data transcoded as it is read. For example, encoding: "UTF-32BE:UTF-8" would read UTF-32BE data from the file but transcode it to UTF-8 before CSV parses it.

This method wraps a String you provide, or an empty default String, in a CSV object which is passed to the provided block. You can use the block to append CSV rows to the String and when the block exits, the final String will be returned.

Note that a passed String is modified by this method. Call dup() before passing if you need a new String.

The options parameter can be anything CSV::new() understands. This method understands an additional :encoding parameter when not passed a String to set the base Encoding for the output. CSV needs this hint if you plan to output non-ASCII compatible data.

This method is a shortcut for converting a single row (Array) into a CSV String.

The options parameter can be anything CSV::new() understands. This method understands an additional :encoding parameter to set the base Encoding for the output. This method will try to guess your Encoding from the first non-nil field in row, if possible, but you may need to use this parameter as a backup plan.

The :row_sep option defaults to $INPUT_RECORD_SEPARATOR ($/) when calling this method.

This method will return a CSV instance, just like CSV::new(), but the instance will be cached and returned for all future calls to this method for the same data object (tested by Object#object_id()) with the same options.

If a block is given, the instance is passed to the block and the return value becomes the return value of the block.

This constructor will wrap either a String or IO object passed in data for reading and/or writing. In addition to the CSV instance methods, several IO methods are delegated. (See CSV::open() for a complete list.) If you pass a String for data, you can later retrieve it (after writing to it, for example) with CSV.string().

Note that a wrapped String will be positioned at the beginning (for reading). If you want it at the end (for writing), use CSV::generate(). If you want any other positioning, pass a preset StringIO object instead.

You may set any reading and/or writing preferences in the options Hash. Available options are:

:col_sep

The String placed between each field. This String will be transcoded into the data's Encoding before parsing.

:row_sep

The String appended to the end of each row. This can be set to the special :auto setting, which requests that CSV automatically discover this from the data. Auto-discovery reads ahead in the data looking for the next "\r\n", "\n", or "\r" sequence. A sequence will be selected even if it occurs in a quoted field, assuming that you would have the same line endings there. If none of those sequences is found, data is ARGF, STDIN, STDOUT, or STDERR, or the stream is only available for output, the default $INPUT_RECORD_SEPARATOR ($/) is used. Obviously, discovery takes a little time. Set manually if speed is important. Also note that IO objects should be opened in binary mode on Windows if this feature will be used as the line-ending translation can cause problems with resetting the document position to where it was before the read ahead. This String will be transcoded into the data's Encoding before parsing.

:quote_char

The character used to quote fields. This has to be a single character String. This is useful for application that incorrectly use ' as the quote character instead of the correct ". CSV will always consider a double sequence of this character to be an escaped quote. This String will be transcoded into the data's Encoding before parsing.

:field_size_limit

This is a maximum size CSV will read ahead looking for the closing quote for a field. (In truth, it reads to the first line ending beyond this size.) If a quote cannot be found within the limit CSV will raise a MalformedCSVError, assuming the data is faulty. You can use this limit to prevent what are effectively DoS attacks on the parser. However, this limit can cause a legitimate parse to fail and thus is set to nil, or off, by default.

:converters

An Array of names from the Converters Hash and/or lambdas that handle custom conversion. A single converter doesn't have to be in an Array. All built-in converters try to transcode fields to UTF-8 before converting. The conversion will fail if the data cannot be transcoded, leaving the field unchanged.

:unconverted_fields

If set to true, an unconverted_fields() method will be added to all returned rows (Array or CSV::Row) that will return the fields as they were before conversion. Note that :headers supplied by Array or String were not fields of the document and thus will have an empty Array attached.

:headers

If set to :first_row or true, the initial row of the CSV file will be treated as a row of headers. If set to an Array, the contents will be used as the headers. If set to a String, the String is run through a call of CSV::parse_line() with the same :col_sep, :row_sep, and :quote_char as this instance to produce an Array of headers. This setting causes CSV#shift() to return rows as CSV::Row objects instead of Arrays and CSV#read() to return CSV::Table objects instead of an Array of Arrays.

:return_headers

When false, header rows are silently swallowed. If set to true, header rows are returned in a CSV::Row object with identical headers and fields (save that the fields do not go through the converters).

:write_headers

When true and :headers is set, a header row will be added to the output.

:header_converters

Identical in functionality to :converters save that the conversions are only made to header rows. All built-in converters try to transcode headers to UTF-8 before converting. The conversion will fail if the data cannot be transcoded, leaving the header unchanged.

:skip_blanks

When set to a true value, CSV will skip over any empty rows. Note that this setting will not skip rows that contain column separators, even if the rows contain no actual data. If you want to skip rows that contain separators but no content, consider using :skip_lines, or inspecting fields.compact.empty? on each row.

:force_quotes

When set to a true value, CSV will quote all CSV fields it creates.

:skip_lines

When set to an object responding to match, every line matching it is considered a comment and ignored during parsing. When set to a String, it is first converted to a Regexp. When set to nil no line is considered a comment. If the passed object does not respond to match, ArgumentError is thrown.

:liberal_parsing

When set to a true value, CSV will attempt to parse input not conformant with RFC 4180, such as double quotes in unquoted fields.

See CSV::DEFAULT_OPTIONS for the default settings.

Options cannot be overridden in the instance methods for performance reasons, so be sure to set what you want here.

This method opens an IO object, and wraps that with CSV. This is intended as the primary interface for writing a CSV file.

You must pass a filename and may optionally add a mode for Ruby's open(). You may also pass an optional Hash containing any options CSV::new() understands as the final argument.

This method works like Ruby's open() call, in that it will pass a CSV object to a provided block and close it when the block terminates, or it will return the CSV object when no block is provided. (Note: This is different from the Ruby 1.8 CSV library which passed rows to the block. Use CSV::foreach() for that behavior.)

You must provide a mode with an embedded Encoding designator unless your data is in Encoding::default_external(). CSV will check the Encoding of the underlying IO object (set by the mode you pass) to determine how to parse the data. You may provide a second Encoding to have the data transcoded as it is read just as you can with a normal call to IO::open(). For example, "rb:UTF-32BE:UTF-8" would read UTF-32BE data from the file but transcode it to UTF-8 before CSV parses it.

An opened CSV object will delegate to many IO methods for convenience. You may call:

  • binmode()

  • binmode?()

  • close()

  • close_read()

  • close_write()

  • closed?()

  • eof()

  • eof?()

  • external_encoding()

  • fcntl()

  • fileno()

  • flock()

  • flush()

  • fsync()

  • internal_encoding()

  • ioctl()

  • isatty()

  • path()

  • pid()

  • pos()

  • pos=()

  • reopen()

  • seek()

  • stat()

  • sync()

  • sync=()

  • tell()

  • to_i()

  • to_io()

  • truncate()

  • tty?()

This method can be used to easily parse CSV out of a String. You may either provide a block which will be called with each row of the String in turn, or just use the returned Array of Arrays (when no block is given).

You pass your str to read from, and an optional options Hash containing anything CSV::new() understands.

This method is a shortcut for converting a single line of a CSV String into an Array. Note that if line contains multiple rows, anything beyond the first row is ignored.

The options parameter can be anything CSV::new() understands.

Use to slurp a CSV file into an Array of Arrays. Pass the path to the file and any options CSV::new() understands. This method also understands an additional :encoding parameter that you can use to specify the Encoding of the data in the file to be read. You must provide this unless your data is in Encoding::default_external(). CSV will use this to determine how to parse the data. You may provide a second Encoding to have the data transcoded as it is read. For example, encoding: "UTF-32BE:UTF-8" would read UTF-32BE data from the file but transcode it to UTF-8 before CSV parses it.

Alias for CSV::read().

A shortcut for:

CSV.read( path, { headers:           true,
                  converters:        :numeric,
                  header_converters: :symbol }.merge(options) )

Instance Methods


The primary write method for wrapped Strings and IOs, row (an Array or CSV::Row) is converted to CSV and appended to the data source. When a CSV::Row is passed, only the row's fields() are appended to the output.

The data source must be open for writing.

The actual work method for adding converters, used by both CSV.convert() and CSV.header_convert().

This method requires the var_name of the instance variable to place the converters in, the const Hash to lookup named converters in, and the normal parameters of the CSV.convert() and CSV.header_convert() methods.

An alias for <<

This method injects an instance variable unconverted_fields into row and an accessor method for row called unconverted_fields(). The variable is set to the contents of fields.

You can use this method to install a CSV::Converters built-in, or provide a block that handles a custom conversion.

If you provide a block that takes one argument, it will be passed the field and is expected to return the converted value or the field itself. If your block takes two arguments, it will also be passed a CSV::FieldInfo Struct, containing details about the field. Again, the block should return a converted field or the field itself.

Processes fields with @converters, or @header_converters if headers is passed as true, returning the converted field set. Any converter that changes the field into something other than a String halts the pipeline of conversion for that field. This is primarily an efficiency shortcut.

Returns the current list of converters in effect. See CSV::new for details. Built-in converters will be returned by name, while others will be returned as is.

Yields each row of the data source in turn.

Support for Enumerable.

The data source must be open for reading.

Builds a regular expression in @encoding. All chunks will be transcoded to that encoding.

Builds a String in @encoding. All chunks will be transcoded to that encoding.

This method is an encoding safe version of Regexp::escape(). It will escape any characters that would change the meaning of a regular expression in the encoding of str. Regular expression characters that cannot be transcoded to the target encoding will be skipped and no escaping will be performed if a backslash cannot be transcoded.

Returns true if all output fields are quoted. See CSV::new for details.

An alias for shift

Identical to CSV#convert(), but for header rows.

Note that this method must be called before header rows are read to have any effect.

Returns the current list of converters in effect for headers. See CSV::new for details. Built-in converters will be returned by name, while others will be returned as is.

Returns true if the next row read will be a header row.

Returns nil if headers will not be used, true if they will but have not yet been read, or the actual headers after they have been read. See CSV::new for details.

Stores the pattern of comments to skip from the provided options.

The pattern must respond to .match, else ArgumentError is raised. Strings are converted to a Regexp.

See also CSV.new

Loads any converters requested during construction.

If field_name is set :converters (the default) field converters are set. When field_name is :header_converters header converters are added instead.

The :unconverted_fields option is also activated for :converters calls, if requested.

Stores header row settings and loads header converters, if needed.

Pre-compiles parsers and stores them by name for access during reads.

Stores the indicated separators for later use.

If auto-discovery was requested for @row_sep, this method will read ahead in the @io and try to find one. ARGF, STDIN, STDOUT, STDERR and any stream open for output only with a default @row_sep of $INPUT_RECORD_SEPARATOR ($/).

This method also establishes the quoting rules used for CSV output.

Returns a simplified description of the key CSV attributes in an ASCII compatible String.

Returns true if illegal input is handled. See CSV::new for details.

This method is used to turn a finished row into a CSV::Row. Header rows are also dealt with here, either by returning a CSV::Row with identical headers and fields (save that the fields do not go through the converters) or by reading past them to return a field row. Headers are also saved in @headers for use in future rows.

When nil, row is assumed to be a header row not based on an actual row of the stream.

An alias for <<

Returns the encoding of the internal IO object or the default if the encoding cannot be determined.

Slurps the remaining rows and returns an Array of Arrays.

The data source must be open for reading.

An alias for shift
An alias for read

Returns true if headers will be returned as a row of results. See CSV::new for details.

Rewinds the underlying IO object and resets CSV's lineno() counter.

The primary read method for wrapped Strings and IOs, a single row is pulled from the data source, parsed and returned as an Array of fields (if header rows are not used) or a CSV::Row (when header rows are used).

The data source must be open for reading.

Returns true blank lines are skipped by the parser. See CSV::new for details.

Returns true if unconverted_fields() to parsed results. See CSV::new for details.

Returns true if headers are written in output. See CSV::new for details.