Class

CSV

CSV (comma-separated variables) data is a text representation of a table:

  • A row separator delimits table rows. A common row separator is the newline character "\n".

  • A column separator delimits fields in a row. A common column separator is the comma character ",".

This CSV String, with row separator "\n" and column separator ",", has three rows and two columns:

"foo,0\nbar,1\nbaz,2\n"

Despite the name CSV, a CSV representation can use different separators.

For more about tables, see the Wikipedia article “Table (information)”, especially its section “Simple table

Class CSV

Class CSV provides methods for:

  • Parsing CSV data from a String object, a File (via its file path), or an IO object.

  • Generating CSV data to a String object.

To make CSV available:

require 'csv'

All examples here assume that this has been done.

Keeping It Simple

A CSV object has dozens of instance methods that offer fine-grained control of parsing and generating CSV data. For many needs, though, simpler approaches will do.

This section summarizes the singleton methods in CSV that allow you to parse and generate without explicitly creating CSV objects. For details, follow the links.

Simple Parsing

Parsing methods commonly return either of:

  • An Array of Arrays of Strings:

    • The outer Array is the entire “table”.

    • Each inner Array is a row.

    • Each String is a field.

  • A CSV::Table object. For details, see CSV with Headers.

Parsing a String

The input to be parsed can be a string:

string = "foo,0\nbar,1\nbaz,2\n"

Method CSV.parse returns the entire CSV data:

CSV.parse(string) # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Method CSV.parse_line returns only the first row:

CSV.parse_line(string) # => ["foo", "0"]

CSV extends class String with instance method String#parse_csv, which also returns only the first row:

string.parse_csv # => ["foo", "0"]

Parsing Via a File Path

The input to be parsed can be in a file:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Method CSV.read returns the entire CSV data:

CSV.read(path) # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Method CSV.foreach iterates, passing each row to the given block:

CSV.foreach(path) do |row|
  p row
end

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

Method CSV.table returns the entire CSV data as a CSV::Table object:

CSV.table(path) # => #<CSV::Table mode:col_or_row row_count:3>

Parsing from an Open IO Stream

The input to be parsed can be in an open IO stream:

Method CSV.read returns the entire CSV data:

File.open(path) do |file|
  CSV.read(file)
end # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

As does method CSV.parse:

File.open(path) do |file|
  CSV.parse(file)
end # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Method CSV.parse_line returns only the first row:

File.open(path) do |file|
 CSV.parse_line(file)
end # => ["foo", "0"]

Method CSV.foreach iterates, passing each row to the given block:

File.open(path) do |file|
  CSV.foreach(file) do |row|
    p row
  end
end

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

Method CSV.table returns the entire CSV data as a CSV::Table object:

File.open(path) do |file|
  CSV.table(file)
end # => #<CSV::Table mode:col_or_row row_count:3>

Simple Generating

Method CSV.generate returns a String; this example uses method CSV#<< to append the rows that are to be generated:

output_string = CSV.generate do |csv|
  csv << ['foo', 0]
  csv << ['bar', 1]
  csv << ['baz', 2]
end
output_string # => "foo,0\nbar,1\nbaz,2\n"

Method CSV.generate_line returns a String containing the single row constructed from an Array:

CSV.generate_line(['foo', '0']) # => "foo,0\n"

CSV extends class Array with instance method Array#to_csv, which forms an Array into a String:

['foo', '0'].to_csv # => "foo,0\n"

“Filtering” CSV

Method CSV.filter provides a Unix-style filter for CSV data. The input data is processed to form the output data:

in_string = "foo,0\nbar,1\nbaz,2\n"
out_string = ''
CSV.filter(in_string, out_string) do |row|
  row[0] = row[0].upcase
  row[1] *= 4
end
out_string # => "FOO,0000\nBAR,1111\nBAZ,2222\n"

CSV Objects

There are three ways to create a CSV object:

  • Method CSV.new returns a new CSV object.

  • Method CSV.instance returns a new or cached CSV object.

  • Method CSV() also returns a new or cached CSV object.

Instance Methods

CSV has three groups of instance methods:

  • Its own internally defined instance methods.

  • Methods included by module Enumerable.

  • Methods delegated to class IO. See below.

Delegated Methods

For convenience, a CSV object will delegate to many methods in class IO. (A few have wrapper “guard code” in CSV.) You may call:

Options

The default values for options are:

DEFAULT_OPTIONS = {
  # For both parsing and generating.
  col_sep:            ",",
  row_sep:            :auto,
  quote_char:         '"',
  # For parsing.
  field_size_limit:   nil,
  converters:         nil,
  unconverted_fields: nil,
  headers:            false,
  return_headers:     false,
  header_converters:  nil,
  skip_blanks:        false,
  skip_lines:         nil,
  liberal_parsing:    false,
  nil_value:          nil,
  empty_value:        "",
  # For generating.
  write_headers:      nil,
  quote_empty:        true,
  force_quotes:       false,
  write_converters:   nil,
  write_nil_value:    nil,
  write_empty_value:  "",
  strip:              false,
}

Options for Parsing

Options for parsing, described in detail below, include:

  • row_sep: Specifies the row separator; used to delimit rows.

  • col_sep: Specifies the column separator; used to delimit fields.

  • quote_char: Specifies the quote character; used to quote fields.

  • field_size_limit: Specifies the maximum field size allowed.

  • converters: Specifies the field converters to be used.

  • unconverted_fields: Specifies whether unconverted fields are to be available.

  • headers: Specifies whether data contains headers, or specifies the headers themselves.

  • return_headers: Specifies whether headers are to be returned.

  • header_converters: Specifies the header converters to be used.

  • skip_blanks: Specifies whether blanks lines are to be ignored.

  • skip_lines: Specifies how comments lines are to be recognized.

  • strip: Specifies whether leading and trailing whitespace are to be stripped from fields..

  • liberal_parsing: Specifies whether CSV should attempt to parse non-compliant data.

  • nil_value: Specifies the object that is to be substituted for each null (no-text) field.

  • empty_value: Specifies the object that is to be substituted for each empty field.

Option row_sep

Specifies the row separator, a String or the Symbol :auto (see below), to be used for both parsing and generating.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:row_sep) # => :auto

When row_sep is a String, that String becomes the row separator. The String will be transcoded into the data's Encoding before use.

Using "\n":

row_sep = "\n"
str = CSV.generate(row_sep: row_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0\nbar,1\nbaz,2\n"
ary = CSV.parse(str)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using | (pipe):

row_sep = '|'
str = CSV.generate(row_sep: row_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0|bar,1|baz,2|"
ary = CSV.parse(str, row_sep: row_sep)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using -- (two hyphens):

row_sep = '--'
str = CSV.generate(row_sep: row_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0--bar,1--baz,2--"
ary = CSV.parse(str, row_sep: row_sep)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using '' (empty string):

row_sep = ''
str = CSV.generate(row_sep: row_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0bar,1baz,2"
ary = CSV.parse(str, row_sep: row_sep)
ary # => [["foo", "0bar", "1baz", "2"]]

When row_sep is the Symbol :auto (the default), generating uses "\n" as the row separator:

str = CSV.generate do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0\nbar,1\nbaz,2\n"

Parsing, on the other hand, invokes auto-discovery of the row separator.

Auto-discovery reads ahead in the data looking for the next \r\n, \n, or \r sequence. The sequence will be selected even if it occurs in a quoted field, assuming that you would have the same line endings there.

Example:

str = CSV.generate do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0\nbar,1\nbaz,2\n"
ary = CSV.parse(str)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

The default $INPUT_RECORD_SEPARATOR ($/) is used if any of the following is true:

  • None of those sequences is found.

  • Data is ARGF, STDIN, STDOUT, or STDERR.

  • The stream is only available for output.

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.


Raises an exception if the given value is not String-convertible:

row_sep = BasicObject.new
# Raises NoMethodError (undefined method `to_s' for #<BasicObject:>)
CSV.generate(ary, row_sep: row_sep)
# Raises NoMethodError (undefined method `to_s' for #<BasicObject:>)
CSV.parse(str, row_sep: row_sep)
Option col_sep

Specifies the String field separator to be used for both parsing and generating. The String will be transcoded into the data's Encoding before use.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:col_sep) # => "," (comma)

Using the default (comma):

str = CSV.generate do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0\nbar,1\nbaz,2\n"
ary = CSV.parse(str)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using : (colon):

col_sep = ':'
str = CSV.generate(col_sep: col_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo:0\nbar:1\nbaz:2\n"
ary = CSV.parse(str, col_sep: col_sep)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using :: (two colons):

col_sep = '::'
str = CSV.generate(col_sep: col_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo::0\nbar::1\nbaz::2\n"
ary = CSV.parse(str, col_sep: col_sep)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using '' (empty string):

col_sep = ''
str = CSV.generate(col_sep: col_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo0\nbar1\nbaz2\n"

Raises an exception if parsing with the empty String:

col_sep = ''
# Raises ArgumentError (:col_sep must be 1 or more characters: "")
CSV.parse("foo0\nbar1\nbaz2\n", col_sep: col_sep)

Raises an exception if the given value is not String-convertible:

col_sep = BasicObject.new
# Raises NoMethodError (undefined method `to_s' for #<BasicObject:>)
CSV.generate(line, col_sep: col_sep)
# Raises NoMethodError (undefined method `to_s' for #<BasicObject:>)
CSV.parse(str, col_sep: col_sep)
Option quote_char

Specifies the character (String of length 1) used used to quote fields in both parsing and generating. This String will be transcoded into the data's Encoding before use.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:quote_char) # => "\"" (double quote)

This is useful for an application that incorrectly uses ' (single-quote) to quote fields, instead of the correct " (double-quote).

Using the default (double quote):

str = CSV.generate do |csv|
  csv << ['foo', 0]
  csv << ["'bar'", 1]
  csv << ['"baz"', 2]
end
str # => "foo,0\n'bar',1\n\"\"\"baz\"\"\",2\n"
ary = CSV.parse(str)
ary # => [["foo", "0"], ["'bar'", "1"], ["\"baz\"", "2"]]

Using ' (single-quote):

quote_char = "'"
str = CSV.generate(quote_char: quote_char) do |csv|
  csv << ['foo', 0]
  csv << ["'bar'", 1]
  csv << ['"baz"', 2]
end
str # => "foo,0\n'''bar''',1\n\"baz\",2\n"
ary = CSV.parse(str, quote_char: quote_char)
ary # => [["foo", "0"], ["'bar'", "1"], ["\"baz\"", "2"]]

Raises an exception if the String length is greater than 1:

# Raises ArgumentError (:quote_char has to be nil or a single character String)
CSV.new('', quote_char: 'xx')

Raises an exception if the value is not a String:

# Raises ArgumentError (:quote_char has to be nil or a single character String)
CSV.new('', quote_char: :foo)
Option field_size_limit

Specifies the Integer field size limit.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:field_size_limit) # => nil

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; therefore the default value is nil (no limit).

For the examples in this section:

str = <<~EOT
  "a","b"
  "
  2345
  ",""
EOT
str # => "\"a\",\"b\"\n\"\n2345\n\",\"\"\n"

Using the default nil:

ary = CSV.parse(str)
ary # => [["a", "b"], ["\n2345\n", ""]]

Using 50:

field_size_limit = 50
ary = CSV.parse(str, field_size_limit: field_size_limit)
ary # => [["a", "b"], ["\n2345\n", ""]]

Raises an exception if a field is too long:

big_str = "123456789\n" * 1024
# Raises CSV::MalformedCSVError (Field size exceeded in line 1.)
CSV.parse('valid,fields,"' + big_str + '"', field_size_limit: 2048)
Option converters

Specifies converters to be used in parsing fields. See Field Converters

Default value:

CSV::DEFAULT_OPTIONS.fetch(:converters) # => nil

The value may be a field converter name (see Stored Converters):

str = '1,2,3'
# Without a converter
array = CSV.parse_line(str)
array # => ["1", "2", "3"]
# With built-in converter :integer
array = CSV.parse_line(str, converters: :integer)
array # => [1, 2, 3]

The value may be a converter list (see Converter Lists):

str = '1,3.14159'
# Without converters
array = CSV.parse_line(str)
array # => ["1", "3.14159"]
# With built-in converters
array = CSV.parse_line(str, converters: [:integer, :float])
array # => [1, 3.14159]

The value may be a Proc custom converter: (see Custom Field Converters):

str = ' foo  ,  bar  ,  baz  '
# Without a converter
array = CSV.parse_line(str)
array # => [" foo  ", "  bar  ", "  baz  "]
# With a custom converter
array = CSV.parse_line(str, converters: proc {|field| field.strip })
array # => ["foo", "bar", "baz"]

See also Custom Field Converters


Raises an exception if the converter is not a converter name or a Proc:

str = 'foo,0'
# Raises NoMethodError (undefined method `arity' for nil:NilClass)
CSV.parse(str, converters: :foo)
Option unconverted_fields

Specifies the boolean that determines whether unconverted field values are to be available.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:unconverted_fields) # => nil

The unconverted field values are those found in the source data, prior to any conversions performed via option converters.

When option unconverted_fields is true, each returned row (Array or CSV::Row) has an added method, unconverted_fields, that returns the unconverted field values:

str = <<-EOT
foo,0
bar,1
baz,2
EOT
# Without unconverted_fields
csv = CSV.parse(str, converters: :integer)
csv # => [["foo", 0], ["bar", 1], ["baz", 2]]
csv.first.respond_to?(:unconverted_fields) # => false
# With unconverted_fields
csv = CSV.parse(str, converters: :integer, unconverted_fields: true)
csv # => [["foo", 0], ["bar", 1], ["baz", 2]]
csv.first.respond_to?(:unconverted_fields) # => true
csv.first.unconverted_fields # => ["foo", "0"]
Option headers

Specifies a boolean, Symbol, Array, or String to be used to define column headers.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:headers) # => false

Without headers:

str = <<-EOT
Name,Count
foo,0
bar,1
bax,2
EOT
csv = CSV.new(str)
csv # => #<CSV io_type:StringIO encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">
csv.headers # => nil
csv.shift # => ["Name", "Count"]

If set to true or the Symbol :first_row, the first row of the data is treated as a row of headers:

str = <<-EOT
Name,Count
foo,0
bar,1
bax,2
EOT
csv = CSV.new(str, headers: true)
csv # => #<CSV io_type:StringIO encoding:UTF-8 lineno:2 col_sep:"," row_sep:"\n" quote_char:"\"" headers:["Name", "Count"]>
csv.headers # => ["Name", "Count"]
csv.shift # => #<CSV::Row "Name":"bar" "Count":"1">

If set to an Array, the Array elements are treated as headers:

str = <<-EOT
foo,0
bar,1
bax,2
EOT
csv = CSV.new(str, headers: ['Name', 'Count'])
csv
csv.headers # => ["Name", "Count"]
csv.shift # => #<CSV::Row "Name":"bar" "Count":"1">

If set to a String str, method CSV::parse_line(str, options) is called with the current options, and the returned Array is treated as headers:

str = <<-EOT
foo,0
bar,1
bax,2
EOT
csv = CSV.new(str, headers: 'Name,Count')
csv
csv.headers # => ["Name", "Count"]
csv.shift # => #<CSV::Row "Name":"bar" "Count":"1">
Option return_headers

Specifies the boolean that determines whether method shift returns or ignores the header row.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:return_headers) # => false

Examples:

str = <<-EOT
Name,Count
foo,0
bar,1
bax,2
EOT
# Without return_headers first row is str.
csv = CSV.new(str, headers: true)
csv.shift # => #<CSV::Row "Name":"foo" "Count":"0">
# With return_headers first row is headers.
csv = CSV.new(str, headers: true, return_headers: true)
csv.shift # => #<CSV::Row "Name":"Name" "Count":"Count">
Option header_converters

Specifies converters to be used in parsing headers. See Header Converters

Default value:

CSV::DEFAULT_OPTIONS.fetch(:header_converters) # => nil

Identical in functionality to option converters except that:

  • The converters apply only to the header row.

  • The built-in header converters are :downcase and :symbol.

This section assumes prior execution of:

str = <<-EOT
Name,Value
foo,0
bar,1
baz,2
EOT
# With no header converter
table = CSV.parse(str, headers: true)
table.headers # => ["Name", "Value"]

The value may be a header converter name (see Stored Converters):

table = CSV.parse(str, headers: true, header_converters: :downcase)
table.headers # => ["name", "value"]

The value may be a converter list (see Converter Lists):

header_converters = [:downcase, :symbol]
table = CSV.parse(str, headers: true, header_converters: header_converters)
table.headers # => [:name, :value]

The value may be a Proc custom converter (see Custom Header Converters):

upcase_converter = proc {|field| field.upcase }
table = CSV.parse(str, headers: true, header_converters: upcase_converter)
table.headers # => ["NAME", "VALUE"]

See also Custom Header Converters

Option skip_blanks

Specifies a boolean that determines whether blank lines in the input will be ignored; a line that contains a column separator is not considered to be blank.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:skip_blanks) # => false

See also option skiplines.

For examples in this section:

str = <<-EOT
foo,0

bar,1
baz,2

,
EOT

Using the default, false:

ary = CSV.parse(str)
ary # => [["foo", "0"], [], ["bar", "1"], ["baz", "2"], [], [nil, nil]]

Using true:

ary = CSV.parse(str, skip_blanks: true)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"], [nil, nil]]

Using a truthy value:

ary = CSV.parse(str, skip_blanks: :foo)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"], [nil, nil]]
Option skip_lines

Specifies an object to use in identifying comment lines in the input that are to be ignored:

  • If a Regexp, ignores lines that match it.

  • If a String, converts it to a Regexp, ignores lines that match it.

  • If nil, no lines are considered to be comments.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:skip_lines) # => nil

For examples in this section:

str = <<-EOT
# Comment
foo,0
bar,1
baz,2
# Another comment
EOT
str # => "# Comment\nfoo,0\nbar,1\nbaz,2\n# Another comment\n"

Using the default, nil:

ary = CSV.parse(str)
ary # => [["# Comment"], ["foo", "0"], ["bar", "1"], ["baz", "2"], ["# Another comment"]]

Using a Regexp:

ary = CSV.parse(str, skip_lines: /^#/)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using a String:

ary = CSV.parse(str, skip_lines: '#')
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Raises an exception if given an object that is not a Regexp, a String, or nil:

# Raises ArgumentError (:skip_lines has to respond to #match: 0)
CSV.parse(str, skip_lines: 0)
Option strip

Specifies the boolean value that determines whether whitespace is stripped from each input field.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:strip) # => false

With default value false:

ary = CSV.parse_line(' a , b ')
ary # => [" a ", " b "]

With value true:

ary = CSV.parse_line(' a , b ', strip: true)
ary # => ["a", "b"]
Option liberal_parsing

Specifies the boolean value that determines whether CSV will attempt to parse input not conformant with RFC 4180, such as double quotes in unquoted fields.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:liberal_parsing) # => false

For examples in this section:

str = 'is,this "three, or four",fields'

Without liberal_parsing:

# Raises CSV::MalformedCSVError (Illegal quoting in str 1.)
CSV.parse_line(str)

With liberal_parsing:

ary = CSV.parse_line(str, liberal_parsing: true)
ary # => ["is", "this \"three", " or four\"", "fields"]
Option nil_value

Specifies the object that is to be substituted for each null (no-text) field.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:nil_value) # => nil

With the default, nil:

CSV.parse_line('a,,b,,c') # => ["a", nil, "b", nil, "c"]

With a different object:

CSV.parse_line('a,,b,,c', nil_value: 0) # => ["a", 0, "b", 0, "c"]
Option empty_value

Specifies the object that is to be substituted for each field that has an empty String.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:empty_value) # => "" (empty string)

With the default, "":

CSV.parse_line('a,"",b,"",c') # => ["a", "", "b", "", "c"]

With a different object:

CSV.parse_line('a,"",b,"",c', empty_value: 'x') # => ["a", "x", "b", "x", "c"]

Options for Generating

Options for generating, described in detail below, include:

  • row_sep: Specifies the row separator; used to delimit rows.

  • col_sep: Specifies the column separator; used to delimit fields.

  • quote_char: Specifies the quote character; used to quote fields.

  • write_headers: Specifies whether headers are to be written.

  • force_quotes: Specifies whether each output field is to be quoted.

  • quote_empty: Specifies whether each empty output field is to be quoted.

  • write_converters: Specifies the field converters to be used in writing.

  • write_nil_value: Specifies the object that is to be substituted for each nil-valued field.

  • write_empty_value: Specifies the object that is to be substituted for each empty field.

Option row_sep

Specifies the row separator, a String or the Symbol :auto (see below), to be used for both parsing and generating.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:row_sep) # => :auto

When row_sep is a String, that String becomes the row separator. The String will be transcoded into the data's Encoding before use.

Using "\n":

row_sep = "\n"
str = CSV.generate(row_sep: row_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0\nbar,1\nbaz,2\n"
ary = CSV.parse(str)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using | (pipe):

row_sep = '|'
str = CSV.generate(row_sep: row_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0|bar,1|baz,2|"
ary = CSV.parse(str, row_sep: row_sep)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using -- (two hyphens):

row_sep = '--'
str = CSV.generate(row_sep: row_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0--bar,1--baz,2--"
ary = CSV.parse(str, row_sep: row_sep)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using '' (empty string):

row_sep = ''
str = CSV.generate(row_sep: row_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0bar,1baz,2"
ary = CSV.parse(str, row_sep: row_sep)
ary # => [["foo", "0bar", "1baz", "2"]]

When row_sep is the Symbol :auto (the default), generating uses "\n" as the row separator:

str = CSV.generate do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0\nbar,1\nbaz,2\n"

Parsing, on the other hand, invokes auto-discovery of the row separator.

Auto-discovery reads ahead in the data looking for the next \r\n, \n, or \r sequence. The sequence will be selected even if it occurs in a quoted field, assuming that you would have the same line endings there.

Example:

str = CSV.generate do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0\nbar,1\nbaz,2\n"
ary = CSV.parse(str)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

The default $INPUT_RECORD_SEPARATOR ($/) is used if any of the following is true:

  • None of those sequences is found.

  • Data is ARGF, STDIN, STDOUT, or STDERR.

  • The stream is only available for output.

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.


Raises an exception if the given value is not String-convertible:

row_sep = BasicObject.new
# Raises NoMethodError (undefined method `to_s' for #<BasicObject:>)
CSV.generate(ary, row_sep: row_sep)
# Raises NoMethodError (undefined method `to_s' for #<BasicObject:>)
CSV.parse(str, row_sep: row_sep)
Option col_sep

Specifies the String field separator to be used for both parsing and generating. The String will be transcoded into the data's Encoding before use.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:col_sep) # => "," (comma)

Using the default (comma):

str = CSV.generate do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo,0\nbar,1\nbaz,2\n"
ary = CSV.parse(str)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using : (colon):

col_sep = ':'
str = CSV.generate(col_sep: col_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo:0\nbar:1\nbaz:2\n"
ary = CSV.parse(str, col_sep: col_sep)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using :: (two colons):

col_sep = '::'
str = CSV.generate(col_sep: col_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo::0\nbar::1\nbaz::2\n"
ary = CSV.parse(str, col_sep: col_sep)
ary # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Using '' (empty string):

col_sep = ''
str = CSV.generate(col_sep: col_sep) do |csv|
  csv << [:foo, 0]
  csv << [:bar, 1]
  csv << [:baz, 2]
end
str # => "foo0\nbar1\nbaz2\n"

Raises an exception if parsing with the empty String:

col_sep = ''
# Raises ArgumentError (:col_sep must be 1 or more characters: "")
CSV.parse("foo0\nbar1\nbaz2\n", col_sep: col_sep)

Raises an exception if the given value is not String-convertible:

col_sep = BasicObject.new
# Raises NoMethodError (undefined method `to_s' for #<BasicObject:>)
CSV.generate(line, col_sep: col_sep)
# Raises NoMethodError (undefined method `to_s' for #<BasicObject:>)
CSV.parse(str, col_sep: col_sep)
Option quote_char

Specifies the character (String of length 1) used used to quote fields in both parsing and generating. This String will be transcoded into the data's Encoding before use.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:quote_char) # => "\"" (double quote)

This is useful for an application that incorrectly uses ' (single-quote) to quote fields, instead of the correct " (double-quote).

Using the default (double quote):

str = CSV.generate do |csv|
  csv << ['foo', 0]
  csv << ["'bar'", 1]
  csv << ['"baz"', 2]
end
str # => "foo,0\n'bar',1\n\"\"\"baz\"\"\",2\n"
ary = CSV.parse(str)
ary # => [["foo", "0"], ["'bar'", "1"], ["\"baz\"", "2"]]

Using ' (single-quote):

quote_char = "'"
str = CSV.generate(quote_char: quote_char) do |csv|
  csv << ['foo', 0]
  csv << ["'bar'", 1]
  csv << ['"baz"', 2]
end
str # => "foo,0\n'''bar''',1\n\"baz\",2\n"
ary = CSV.parse(str, quote_char: quote_char)
ary # => [["foo", "0"], ["'bar'", "1"], ["\"baz\"", "2"]]

Raises an exception if the String length is greater than 1:

# Raises ArgumentError (:quote_char has to be nil or a single character String)
CSV.new('', quote_char: 'xx')

Raises an exception if the value is not a String:

# Raises ArgumentError (:quote_char has to be nil or a single character String)
CSV.new('', quote_char: :foo)
Option write_headers

Specifies the boolean that determines whether a header row is included in the output; ignored if there are no headers.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:write_headers) # => nil

Without write_headers:

file_path = 't.csv'
CSV.open(file_path,'w',
    :headers => ['Name','Value']
  ) do |csv|
    csv << ['foo', '0']
end
CSV.open(file_path) do |csv|
  csv.shift
end # => ["foo", "0"]

With write_headers“:

CSV.open(file_path,'w',
    :write_headers=> true,
    :headers => ['Name','Value']
  ) do |csv|
    csv << ['foo', '0']
end
CSV.open(file_path) do |csv|
  csv.shift
end # => ["Name", "Value"]
Option force_quotes

Specifies the boolean that determines whether each output field is to be double-quoted.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:force_quotes) # => false

For examples in this section:

ary = ['foo', 0, nil]

Using the default, false:

str = CSV.generate_line(ary)
str # => "foo,0,\n"

Using true:

str = CSV.generate_line(ary, force_quotes: true)
str # => "\"foo\",\"0\",\"\"\n"
Option quote_empty

Specifies the boolean that determines whether an empty value is to be double-quoted.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:quote_empty) # => true

With the default true:

CSV.generate_line(['"', ""]) # => "\"\"\"\",\"\"\n"

With false:

CSV.generate_line(['"', ""], quote_empty: false) # => "\"\"\"\",\n"
Option write_converters

Specifies converters to be used in generating fields. See Write Converters

Default value:

CSV::DEFAULT_OPTIONS.fetch(:write_converters) # => nil

With no write converter:

str = CSV.generate_line(["\na\n", "\tb\t", " c "])
str # => "\"\na\n\",\tb\t, c \n"

With a write converter:

strip_converter = proc {|field| field.strip }
str = CSV.generate_line(["\na\n", "\tb\t", " c "], write_converters: strip_converter)
str # => "a,b,c\n"

With two write converters (called in order):

upcase_converter = proc {|field| field.upcase }
downcase_converter = proc {|field| field.downcase }
write_converters = [upcase_converter, downcase_converter]
str = CSV.generate_line(['a', 'b', 'c'], write_converters: write_converters)
str # => "a,b,c\n"

See also Write Converters


Raises an exception if the converter returns a value that is neither nil nor String-convertible:

bad_converter = proc {|field| BasicObject.new }
# Raises NoMethodError (undefined method `is_a?' for #<BasicObject:>)
CSV.generate_line(['a', 'b', 'c'], write_converters: bad_converter)#
Option write_nil_value

Specifies the object that is to be substituted for each nil-valued field.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:write_nil_value) # => nil

Without the option:

str = CSV.generate_line(['a', nil, 'c', nil])
str # => "a,,c,\n"

With the option:

str = CSV.generate_line(['a', nil, 'c', nil], write_nil_value: "x")
str # => "a,x,c,x\n"
Option write_empty_value

Specifies the object that is to be substituted for each field that has an empty String.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:write_empty_value) # => ""

Without the option:

str = CSV.generate_line(['a', '', 'c', ''])
str # => "a,\"\",c,\"\"\n"

With the option:

str = CSV.generate_line(['a', '', 'c', ''], write_empty_value: "x")
str # => "a,x,c,x\n"

CSV with Headers

CSV allows to specify column names of CSV file, whether they are in data, or provided separately. If headers are specified, reading methods return an instance of CSV::Table, consisting of CSV::Row.

# Headers are part of data
data = CSV.parse(<<~ROWS, headers: true)
  Name,Department,Salary
  Bob,Engineering,1000
  Jane,Sales,2000
  John,Management,5000
ROWS

data.class      #=> CSV::Table
data.first      #=> #<CSV::Row "Name":"Bob" "Department":"Engineering" "Salary":"1000">
data.first.to_h #=> {"Name"=>"Bob", "Department"=>"Engineering", "Salary"=>"1000"}

# Headers provided by developer
data = CSV.parse('Bob,Engineering,1000', headers: %i[name department salary])
data.first      #=> #<CSV::Row name:"Bob" department:"Engineering" salary:"1000">

Converters

By default, each value (field or header) parsed by CSV is formed into a String. You can use a field converter or header converter to intercept and modify the parsed values:

Also by default, each value to be written during generation is written 'as-is'. You can use a write converter to modify values before writing.

Specifying Converters

You can specify converters for parsing or generating in the options argument to various CSV methods:

  • Option converters for converting parsed field values.

  • Option header_converters for converting parsed header values.

  • Option write_converters for converting values to be written (generated).

There are three forms for specifying converters:

  • A converter proc: executable code to be used for conversion.

  • A converter name: the name of a stored converter.

  • A converter list: an array of converter procs, converter names, and converter lists.

Converter Procs

This converter proc, strip_converter, accepts a value field and returns field.strip:

strip_converter = proc {|field| field.strip }

In this call to CSV.parse, the keyword argument converters: string_converter specifies that:

  • Proc string_converter is to be called for each parsed field.

  • The converter's return value is to replace the field value.

Example:

string = " foo , 0 \n bar , 1 \n baz , 2 \n"
array = CSV.parse(string, converters: strip_converter)
array # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

A converter proc can receive a second argument, field_info, that contains details about the field. This modified strip_converter displays its arguments:

strip_converter = proc do |field, field_info|
  p [field, field_info]
  field.strip
end
string = " foo , 0 \n bar , 1 \n baz , 2 \n"
array = CSV.parse(string, converters: strip_converter)
array # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Output:

[" foo ", #<struct CSV::FieldInfo index=0, line=1, header=nil>]
[" 0 ", #<struct CSV::FieldInfo index=1, line=1, header=nil>]
[" bar ", #<struct CSV::FieldInfo index=0, line=2, header=nil>]
[" 1 ", #<struct CSV::FieldInfo index=1, line=2, header=nil>]
[" baz ", #<struct CSV::FieldInfo index=0, line=3, header=nil>]
[" 2 ", #<struct CSV::FieldInfo index=1, line=3, header=nil>]

Each CSV::Info object shows:

  • The 0-based field index.

  • The 1-based line index.

  • The field header, if any.

Stored Converters

A converter may be given a name and stored in a structure where the parsing methods can find it by name.

The storage structure for field converters is the Hash CSV::Converters. It has several built-in converter procs:

  • :integer: converts each String-embedded integer into a true Integer.

  • :float: converts each String-embedded float into a true Float.

  • :date: converts each String-embedded date into a true Date.

  • :date_time: converts each String-embedded date-time into a true DateTime

. This example creates a converter proc, then stores it:

strip_converter = proc {|field| field.strip }
CSV::Converters[:strip] = strip_converter

Then the parsing method call can refer to the converter by its name, :strip:

string = " foo , 0 \n bar , 1 \n baz , 2 \n"
array = CSV.parse(string, converters: :strip)
array # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

The storage structure for header converters is the Hash CSV::HeaderConverters, which works in the same way. It also has built-in converter procs:

  • :downcase: Downcases each header.

  • :symbol: Converts each header to a Symbol.

There is no such storage structure for write headers.

Converter Lists

A converter list is an Array that may include any assortment of:

  • Converter procs.

  • Names of stored converters.

  • Nested converter lists.

Examples:

numeric_converters = [:integer, :float]
date_converters = [:date, :date_time]
[numeric_converters, strip_converter]
[strip_converter, date_converters, :float]

Like a converter proc, a converter list may be named and stored in either CSV::Converters or CSV::HeaderConverters:

CSV::Converters[:custom] = [strip_converter, date_converters, :float]
CSV::HeaderConverters[:custom] = [:downcase, :symbol]

There are two built-in converter lists:

CSV::Converters[:numeric] # => [:integer, :float]
CSV::Converters[:all] # => [:date_time, :numeric]

Field Converters

With no conversion, all parsed fields in all rows become Strings:

string = "foo,0\nbar,1\nbaz,2\n"
ary = CSV.parse(string)
ary # => # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

When you specify a field converter, each parsed field is passed to the converter; its return value becomes the stored value for the field. A converter might, for example, convert an integer embedded in a String into a true Integer. (In fact, that's what built-in field converter :integer does.)

There are three ways to use field converters.

  • Using option converters with a parsing method:

    ary = CSV.parse(string, converters: :integer)
    ary # => [0, 1, 2] # => [["foo", 0], ["bar", 1], ["baz", 2]]
    
  • Using option converters with a new CSV instance:

    csv = CSV.new(string, converters: :integer)
    # Field converters in effect:
    csv.converters # => [:integer]
    csv.read # => [["foo", 0], ["bar", 1], ["baz", 2]]
    
  • Using method convert to add a field converter to a CSV instance:

    csv = CSV.new(string)
    # Add a converter.
    csv.convert(:integer)
    csv.converters # => [:integer]
    csv.read # => [["foo", 0], ["bar", 1], ["baz", 2]]
    

Installing a field converter does not affect already-read rows:

csv = CSV.new(string)
csv.shift # => ["foo", "0"]
# Add a converter.
csv.convert(:integer)
csv.converters # => [:integer]
csv.read # => [["bar", 1], ["baz", 2]]

There are additional built-in converters, and custom converters are also supported.

Built-In Field Converters

The built-in field converters are in Hash CSV::Converters:

  • Each key is a field converter name.

  • Each value is one of:

    • A Proc field converter.

    • An Array of field converter names.

Display:

CSV::Converters.each_pair do |name, value|
  if value.kind_of?(Proc)
    p [name, value.class]
  else
    p [name, value]
  end
end

Output:

[:integer, Proc]
[:float, Proc]
[:numeric, [:integer, :float]]
[:date, Proc]
[:date_time, Proc]
[:all, [:date_time, :numeric]]

Each of these converters transcodes values to UTF-8 before attempting conversion. If a value cannot be transcoded to UTF-8 the conversion will fail and the value will remain unconverted.

Converter :integer converts each field that Integer() accepts:

data = '0,1,2,x'
# Without the converter
csv = CSV.parse_line(data)
csv # => ["0", "1", "2", "x"]
# With the converter
csv = CSV.parse_line(data, converters: :integer)
csv # => [0, 1, 2, "x"]

Converter :float converts each field that Float() accepts:

data = '1.0,3.14159,x'
# Without the converter
csv = CSV.parse_line(data)
csv # => ["1.0", "3.14159", "x"]
# With the converter
csv = CSV.parse_line(data, converters: :float)
csv # => [1.0, 3.14159, "x"]

Converter :numeric converts with both :integer and :float..

Converter :date converts each field that Date::parse accepts:

data = '2001-02-03,x'
# Without the converter
csv = CSV.parse_line(data)
csv # => ["2001-02-03", "x"]
# With the converter
csv = CSV.parse_line(data, converters: :date)
csv # => [#<Date: 2001-02-03 ((2451944j,0s,0n),+0s,2299161j)>, "x"]

Converter :date_time converts each field that DateTime::parse accepts:

data = '2020-05-07T14:59:00-05:00,x'
# Without the converter
csv = CSV.parse_line(data)
csv # => ["2020-05-07T14:59:00-05:00", "x"]
# With the converter
csv = CSV.parse_line(data, converters: :date_time)
csv # => [#<DateTime: 2020-05-07T14:59:00-05:00 ((2458977j,71940s,0n),-18000s,2299161j)>, "x"]

Converter :numeric converts with both :date_time and :numeric..

As seen above, method convert adds converters to a CSV instance, and method converters returns an Array of the converters in effect:

csv = CSV.new('0,1,2')
csv.converters # => []
csv.convert(:integer)
csv.converters # => [:integer]
csv.convert(:date)
csv.converters # => [:integer, :date]
Custom Field Converters

You can define a custom field converter:

strip_converter = proc {|field| field.strip }
string = " foo , 0 \n bar , 1 \n baz , 2 \n"
array = CSV.parse(string, converters: strip_converter)
array # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

You can register the converter in Converters Hash, which allows you to refer to it by name:

CSV::Converters[:strip] = strip_converter
string = " foo , 0 \n bar , 1 \n baz , 2 \n"
array = CSV.parse(string, converters: :strip)
array # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Header Converters

Header converters operate only on headers (and not on other rows).

There are three ways to use header converters; these examples use built-in header converter :dowhcase, which downcases each parsed header.

  • Option header_converters with a singleton parsing method:

    string = "Name,Count\nFoo,0\n,Bar,1\nBaz,2"
    tbl = CSV.parse(string, headers: true, header_converters: :downcase)
    tbl.class # => CSV::Table
    tbl.headers # => ["name", "count"]
    
  • Option header_converters with a new CSV instance:

    csv = CSV.new(string, header_converters: :downcase)
    # Header converters in effect:
    csv.header_converters # => [:downcase]
    tbl = CSV.parse(string, headers: true)
    tbl.headers # => ["Name", "Count"]
    
  • Method header_convert adds a header converter to a CSV instance:

    csv = CSV.new(string)
    # Add a header converter.
    csv.header_convert(:downcase)
    csv.header_converters # => [:downcase]
    tbl = CSV.parse(string, headers: true)
    tbl.headers # => ["Name", "Count"]
    
Built-In Header Converters

The built-in header converters are in Hash CSV::HeaderConverters. The keys there are the names of the converters:

CSV::HeaderConverters.keys # => [:downcase, :symbol]

Converter :downcase converts each header by downcasing it:

string = "Name,Count\nFoo,0\n,Bar,1\nBaz,2"
tbl = CSV.parse(string, headers: true, header_converters: :downcase)
tbl.class # => CSV::Table
tbl.headers # => ["name", "count"]

Converter :symbol converts each header by making it into a Symbol:

string = "Name,Count\nFoo,0\n,Bar,1\nBaz,2"
tbl = CSV.parse(string, headers: true, header_converters: :symbol)
tbl.headers # => [:name, :count]

Details:

  • Strips leading and trailing whitespace.

  • Downcases the header.

  • Replaces embedded spaces with underscores.

  • Removes non-word characters.

  • Makes the string into a Symbol.

Custom Header Converters

You can define a custom header converter:

upcase_converter = proc {|header| header.upcase }
string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
table = CSV.parse(string, headers: true, header_converters: upcase_converter)
table # => #<CSV::Table mode:col_or_row row_count:4>
table.headers # => ["NAME", "VALUE"]

You can register the converter in HeaderConverters Hash, which allows you to refer to it by name:

CSV::HeaderConverters[:upcase] = upcase_converter
table = CSV.parse(string, headers: true, header_converters: :upcase)
table # => #<CSV::Table mode:col_or_row row_count:4>
table.headers # => ["NAME", "VALUE"]
Write Converters

When you specify a write converter for generating CSV, each field to be written is passed to the converter; its return value becomes the new value for the field. A converter might, for example, strip whitespace from a field.

Using no write converter (all fields unmodified):

output_string = CSV.generate do |csv|
  csv << [' foo ', 0]
  csv << [' bar ', 1]
  csv << [' baz ', 2]
end
output_string # => " foo ,0\n bar ,1\n baz ,2\n"

Using option write_converters with two custom write converters:

strip_converter = proc {|field| field.respond_to?(:strip) ? field.strip : field }
upcase_converter = proc {|field| field.respond_to?(:upcase) ? field.upcase : field }
write_converters = [strip_converter, upcase_converter]
output_string = CSV.generate(write_converters: write_converters) do |csv|
  csv << [' foo ', 0]
  csv << [' bar ', 1]
  csv << [' baz ', 2]
end
output_string # => "FOO,0\nBAR,1\nBAZ,2\n"

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.

A Hash containing the names and Procs for the built-in field converters. See Built-In Field Converters.

This Hash is intentionally left unfrozen, and may be extended with custom field converters. See Custom Field Converters.

Default values for method options.

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.

A Hash containing the names and Procs for the built-in header converters. See Built-In Header Converters.

This Hash is intentionally left unfrozen, and may be extended with custom field converters. See Custom Header Converters.

The version of the installed library.

Class Methods


Reads CSV input and writes CSV output.

For each input row:

  • Forms the data into:

    • A CSV::Row object, if headers are in use.

    • An Array of Arrays, otherwise.

  • Calls the block with that object.

  • Appends the block's return value to the output.

Arguments:

  • CSV source:

    • Argument in_string, if given, should be a String object; it will be put into a new StringIO object positioned at the beginning.

    • Argument in_io, if given, should be an IO object that is open for reading; on return, the IO object will be closed.

    • If neither in_string nor in_io is given, the input stream defaults to ARGF.

  • CSV output:

    • Argument out_string, if given, should be a String object; it will be put into a new StringIO object positioned at the beginning.

    • Argument out_io, if given, should be an IO object that is ppen for writing; on return, the IO object will be closed.

    • If neither out_string nor out_io is given, the output stream defaults to $stdout.

  • Argument options should be keyword arguments.

    • Each argument name that is prefixed with in_ or input_ is stripped of its prefix and is treated as an option for parsing the input. Option input_row_sep defaults to $INPUT_RECORD_SEPARATOR.

    • Each argument name that is prefixed with out_ or output_ is stripped of its prefix and is treated as an option for generating the output. Option output_row_sep defaults to $INPUT_RECORD_SEPARATOR.

    • Each argument not prefixed as above is treated as an option both for parsing the input and for generating the output.

    • See Options for Parsing and Options for Generating.

Example:

in_string = "foo,0\nbar,1\nbaz,2\n"
out_string = ''
CSV.filter(in_string, out_string) do |row|
  row[0] = row[0].upcase
  row[1] *= 4
end
out_string # => "FOO,0000\nBAR,1111\nBAZ,2222\n"

Calls the block with each row read from source path or io.

  • Argument path, if given, must be the path to a file.

  • Argument io should be an IO object that is:

    • Open for reading; on return, the IO object will be closed.

    • Positioned at the beginning. To position at the end, for appending, use method CSV.generate. For any other positioning, pass a preset StringIO object instead.

  • Argument mode, if given, must be a File mode See Open Mode.

  • Arguments **options must be keyword options. See Options for Parsing.

  • This method optionally accepts an additional :encoding option that you can use to specify the Encoding of the data read from path or io. You must provide this unless your data is in the encoding given by Encoding::default_external. Parsing 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 parsing.

Without Option headers

Without option headers, returns each row as an Array object.

These examples assume prior execution of:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Read rows from a file at path:

CSV.foreach(path) {|row| p row }

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

Read rows from an IO object:

File.open(path) do |file|
  CSV.foreach(file) {|row| p row }
end

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

Returns a new Enumerator if no block given:

CSV.foreach(path) # => #<Enumerator: CSV:foreach("t.csv", "r")>
CSV.foreach(File.open(path)) # => #<Enumerator: CSV:foreach(#<File:t.csv>, "r")>

Issues a warning if an encoding is unsupported:

CSV.foreach(File.open(path), encoding: 'foo:bar') {|row| }

Output:

warning: Unsupported encoding foo ignored
warning: Unsupported encoding bar ignored
With Option headers

With option headers, returns each row as a CSV::Row object.

These examples assume prior execution of:

string = "Name,Count\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Read rows from a file at path:

CSV.foreach(path, headers: true) {|row| p row }

Output:

#<CSV::Row "Name":"foo" "Count":"0">
#<CSV::Row "Name":"bar" "Count":"1">
#<CSV::Row "Name":"baz" "Count":"2">

Read rows from an IO object:

File.open(path) do |file|
  CSV.foreach(file, headers: true) {|row| p row }
end

Output:

#<CSV::Row "Name":"foo" "Count":"0">
#<CSV::Row "Name":"bar" "Count":"1">
#<CSV::Row "Name":"baz" "Count":"2">

Raises an exception if path is a String, but not the path to a readable file:

# Raises Errno::ENOENT (No such file or directory @ rb_sysopen - nosuch.csv):
CSV.foreach('nosuch.csv') {|row| }

Raises an exception if io is an IO object, but not open for reading:

io = File.open(path, 'w') {|row| }
# Raises TypeError (no implicit conversion of nil into String):
CSV.foreach(io) {|row| }

Raises an exception if mode is invalid:

# Raises ArgumentError (invalid access mode nosuch):
CSV.foreach(path, 'nosuch') {|row| }
  • Argument csv_string, if given, must be a String object; defaults to a new empty String.

  • Arguments options, if given, should be generating options. See Options for Generating.


Creates a new CSV object via CSV.new(csv_string, **options); calls the block with the CSV object, which the block may modify; returns the String generated from the CSV object.

Note that a passed String is modified by this method. Pass csv_string.dup if the String must be preserved.

This method has one additional option: :encoding, which sets the base Encoding for the output if no no str is specified. CSV needs this hint if you plan to output non-ASCII compatible data.


Add lines:

input_string = "foo,0\nbar,1\nbaz,2\n"
output_string = CSV.generate(input_string) do |csv|
  csv << ['bat', 3]
  csv << ['bam', 4]
end
output_string # => "foo,0\nbar,1\nbaz,2\nbat,3\nbam,4\n"
input_string # => "foo,0\nbar,1\nbaz,2\nbat,3\nbam,4\n"
output_string.equal?(input_string) # => true # Same string, modified

Add lines into new string, preserving old string:

input_string = "foo,0\nbar,1\nbaz,2\n"
output_string = CSV.generate(input_string.dup) do |csv|
  csv << ['bat', 3]
  csv << ['bam', 4]
end
output_string # => "foo,0\nbar,1\nbaz,2\nbat,3\nbam,4\n"
input_string # => "foo,0\nbar,1\nbaz,2\n"
output_string.equal?(input_string) # => false # Different strings

Create lines from nothing:

output_string = CSV.generate do |csv|
  csv << ['foo', 0]
  csv << ['bar', 1]
  csv << ['baz', 2]
end
output_string # => "foo,0\nbar,1\nbaz,2\n"

Raises an exception if csv_string is not a String object:

# Raises TypeError (no implicit conversion of Integer into String)
CSV.generate(0)

Returns the String created by generating CSV from ary using the specified options.

Argument ary must be an Array.

Special options:

  • Option :row_sep defaults to $INPUT_RECORD_SEPARATOR ($/).:

    $INPUT_RECORD_SEPARATOR # => "\n"
    
  • This method accepts an additional option, :encoding, which sets 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.

For other options, see Options for Generating.


Returns the String generated from an Array:

CSV.generate_line(['foo', '0']) # => "foo,0\n"

Raises an exception if ary is not an Array:

# Raises NoMethodError (undefined method `find' for :foo:Symbol)
CSV.generate_line(:foo)

Creates or retrieves cached CSV objects. For arguments and options, see CSV.new.


With no block given, returns a CSV object.

The first call to instance creates and caches a CSV object:

s0 = 's0'
csv0 = CSV.instance(s0)
csv0.class # => CSV

Subsequent calls to instance with that same string or io retrieve that same cached object:

csv1 = CSV.instance(s0)
csv1.class # => CSV
csv1.equal?(csv0) # => true # Same CSV object

A subsequent call to instance with a different string or io creates and caches a different CSV object.

s1 = 's1'
csv2 = CSV.instance(s1)
csv2.equal?(csv0) # => false # Different CSV object

All the cached objects remains available:

csv3 = CSV.instance(s0)
csv3.equal?(csv0) # true # Same CSV object
csv4 = CSV.instance(s1)
csv4.equal?(csv2) # true # Same CSV object

When a block is given, calls the block with the created or retrieved CSV object; returns the block's return value:

CSV.instance(s0) {|csv| :foo } # => :foo

Returns the new CSV object created using string or io and the specified options.

  • Argument string should be a String object; it will be put into a new StringIO object positioned at the beginning.

  • Argument io should be an IO object that is:

    • Open for reading; on return, the IO object will be closed.

    • Positioned at the beginning. To position at the end, for appending, use method CSV.generate. For any other positioning, pass a preset StringIO object instead.

  • Argument options: See:

    For performance reasons, the options cannot be overridden in a CSV object, so those specified here will endure.

In addition to the CSV instance methods, several IO methods are delegated. See Delegated Methods.


Create a CSV object from a String object:

csv = CSV.new('foo,0')
csv # => #<CSV io_type:StringIO encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Create a CSV object from a File object:

File.write('t.csv', 'foo,0')
csv = CSV.new(File.open('t.csv'))
csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Raises an exception if the argument is nil:

# Raises ArgumentError (Cannot parse nil as CSV):
CSV.new(nil)

possible options elements:

hash form:
  :invalid => nil      # raise error on invalid byte sequence (default)
  :invalid => :replace # replace invalid byte sequence
  :undef => :replace   # replace undefined conversion
  :replace => string   # replacement string ("?" or "\uFFFD" if not specified)
  • Argument path, if given, must be the path to a file.

  • Argument io should be an IO object that is:

    • Open for reading; on return, the IO object will be closed.

    • Positioned at the beginning. To position at the end, for appending, use method CSV.generate. For any other positioning, pass a preset StringIO object instead.

  • Argument mode, if given, must be a File mode See Open Mode.

  • Arguments **options must be keyword options. See Options for Generating.

  • This method optionally accepts an additional :encoding option that you can use to specify the Encoding of the data read from path or io. You must provide this unless your data is in the encoding given by Encoding::default_external. Parsing 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 parsing.


These examples assume prior execution of:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

With no block given, returns a new CSV object.

Create a CSV object using a file path:

csv = CSV.open(path)
csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Create a CSV object using an open File:

csv = CSV.open(File.open(path))
csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

With a block given, calls the block with the created CSV object; returns the block's return value:

Using a file path:

csv = CSV.open(path) {|csv| p csv}
csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Output:

#<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Using an open File:

csv = CSV.open(File.open(path)) {|csv| p csv}
csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Output:

#<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Raises an exception if the argument is not a String object or IO object:

# Raises TypeError (no implicit conversion of Symbol into String)
CSV.open(:foo)

Parses string or io using the specified options.

  • Argument string should be a String object; it will be put into a new StringIO object positioned at the beginning.

  • Argument io should be an IO object that is:

    • Open for reading; on return, the IO object will be closed.

    • Positioned at the beginning. To position at the end, for appending, use method CSV.generate. For any other positioning, pass a preset StringIO object instead.

  • Argument options: see Options for Parsing

Without Option headers

Without option headers case.

These examples assume prior execution of:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

With no block given, returns an Array of Arrays formed from the source.

Parse a String:

a_of_a = CSV.parse(string)
a_of_a # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Parse an open File:

a_of_a = File.open(path) do |file|
  CSV.parse(file)
end
a_of_a # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

With a block given, calls the block with each parsed row:

Parse a String:

CSV.parse(string) {|row| p row }

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

Parse an open File:

File.open(path) do |file|
  CSV.parse(file) {|row| p row }
end

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]
With Option headers

With option headers case.

These examples assume prior execution of:

string = "Name,Count\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

With no block given, returns a CSV::Table object formed from the source.

Parse a String:

csv_table = CSV.parse(string, headers: ['Name', 'Count'])
csv_table # => #<CSV::Table mode:col_or_row row_count:5>

Parse an open File:

csv_table = File.open(path) do |file|
  CSV.parse(file, headers: ['Name', 'Count'])
end
csv_table # => #<CSV::Table mode:col_or_row row_count:4>

With a block given, calls the block with each parsed row, which has been formed into a CSV::Row object:

Parse a String:

CSV.parse(string, headers: ['Name', 'Count']) {|row| p row }

Output:

# <CSV::Row "Name":"foo" "Count":"0">
# <CSV::Row "Name":"bar" "Count":"1">
# <CSV::Row "Name":"baz" "Count":"2">

Parse an open File:

File.open(path) do |file|
  CSV.parse(file, headers: ['Name', 'Count']) {|row| p row }
end

Output:

# <CSV::Row "Name":"foo" "Count":"0">
# <CSV::Row "Name":"bar" "Count":"1">
# <CSV::Row "Name":"baz" "Count":"2">

Raises an exception if the argument is not a String object or IO object:

# Raises NoMethodError (undefined method `close' for :foo:Symbol)
CSV.parse(:foo)

Returns the data created by parsing the first line of string or io using the specified options.

  • Argument string should be a String object; it will be put into a new StringIO object positioned at the beginning.

  • Argument io should be an IO object that is:

    • Open for reading; on return, the IO object will be closed.

    • Positioned at the beginning. To position at the end, for appending, use method CSV.generate. For any other positioning, pass a preset StringIO object instead.

  • Argument options: see Options for Parsing

Without Option headers

Without option headers, returns the first row as a new Array.

These examples assume prior execution of:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Parse the first line from a String object:

CSV.parse_line(string) # => ["foo", "0"]

Parse the first line from a File object:

File.open(path) do |file|
  CSV.parse_line(file) # => ["foo", "0"]
end # => ["foo", "0"]

Returns nil if the argument is an empty String:

CSV.parse_line('') # => nil
With Option headers

With option headers, returns the first row as a CSV::Row object.

These examples assume prior execution of:

string = "Name,Count\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Parse the first line from a String object:

CSV.parse_line(string, headers: true) # => #<CSV::Row "Name":"foo" "Count":"0">

Parse the first line from a File object:

File.open(path) do |file|
  CSV.parse_line(file, headers: true)
end # => #<CSV::Row "Name":"foo" "Count":"0">

Raises an exception if the argument is nil:

# Raises ArgumentError (Cannot parse nil as CSV):
CSV.parse_line(nil)

Opens the given source with the given options (see CSV.open), reads the source (see CSV#read), and returns the result, which will be either an Array of Arrays or a CSV::Table.

Without headers:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
CSV.read(path) # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

With headers:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
CSV.read(path, headers: true) # => #<CSV::Table mode:col_or_row row_count:4>

Alias for CSV.read.

Calls CSV.read with source, options, and certain default options:

  • headers: true

  • converbers: :numeric

  • header_converters: :symbol

Returns a CSV::Table object.

Example:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
CSV.table(path) # => #<CSV::Table mode:col_or_row row_count:4>

Instance Methods


Appends a row to self.

  • Argument row must be an Array object or a CSV::Row object.

  • The output stream must be open for writing.


Append Arrays:

CSV.generate do |csv|
  csv << ['foo', 0]
  csv << ['bar', 1]
  csv << ['baz', 2]
end # => "foo,0\nbar,1\nbaz,2\n"

Append CSV::Rows:

headers = []
CSV.generate do |csv|
  csv << CSV::Row.new(headers, ['foo', 0])
  csv << CSV::Row.new(headers, ['bar', 1])
  csv << CSV::Row.new(headers, ['baz', 2])
end # => "foo,0\nbar,1\nbaz,2\n"

Headers in CSV::Row objects are not appended:

headers = ['Name', 'Count']
CSV.generate do |csv|
  csv << CSV::Row.new(headers, ['foo', 0])
  csv << CSV::Row.new(headers, ['bar', 1])
  csv << CSV::Row.new(headers, ['baz', 2])
end # => "foo,0\nbar,1\nbaz,2\n"

Raises an exception if row is not an Array or CSV::Row:

CSV.generate do |csv|
  # Raises NoMethodError (undefined method `collect' for :foo:Symbol)
  csv << :foo
end

Raises an exception if the output stream is not opened for writing:

path = 't.csv'
File.write(path, '')
File.open(path) do |file|
  CSV.open(file) do |csv|
    # Raises IOError (not opened for writing)
    csv << ['foo', 0]
  end
end
An alias for <<
No documentation available
No documentation available
No documentation available
No documentation available
No documentation available

Returns the encoded column separator; used for parsing and writing; see Option col_sep:

CSV.new('').col_sep # => ","
  • With no block, installs a field converter (a Proc).

  • With a block, defines and installs a custom field converter.

  • Returns the Array of installed field converters.

  • Argument converter_name, if given, should be the name of an existing field converter.

See Field Converters.


With no block, installs a field converter:

csv = CSV.new('')
csv.convert(:integer)
csv.convert(:float)
csv.convert(:date)
csv.converters # => [:integer, :float, :date]

The block, if given, is called for each field:

  • Argument field is the field value.

  • Argument field_info is a CSV::FieldInfo object containing details about the field.

The examples here assume the prior execution of:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Example giving a block:

csv = CSV.open(path)
csv.convert {|field, field_info| p [field, field_info]; field.upcase }
csv.read # => [["FOO", "0"], ["BAR", "1"], ["BAZ", "2"]]

Output:

["foo", #<struct CSV::FieldInfo index=0, line=1, header=nil>]
["0", #<struct CSV::FieldInfo index=1, line=1, header=nil>]
["bar", #<struct CSV::FieldInfo index=0, line=2, header=nil>]
["1", #<struct CSV::FieldInfo index=1, line=2, header=nil>]
["baz", #<struct CSV::FieldInfo index=0, line=3, header=nil>]
["2", #<struct CSV::FieldInfo index=1, line=3, header=nil>]

The block need not return a String object:

csv = CSV.open(path)
csv.convert {|field, field_info| field.to_sym }
csv.read # => [[:foo, :"0"], [:bar, :"1"], [:baz, :"2"]]

If converter_name is given, the block is not called:

csv = CSV.open(path)
csv.convert(:integer) {|field, field_info| fail 'Cannot happen' }
csv.read # => [["foo", 0], ["bar", 1], ["baz", 2]]

Raises a parse-time exception if converter_name is not the name of a built-in field converter:

csv = CSV.open(path)
csv.convert(:nosuch) => [nil]
# Raises NoMethodError (undefined method `arity' for nil:NilClass)
csv.read

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 an Array containing field converters; see Field Converters:

csv = CSV.new('')
csv.converters # => []
csv.convert(:integer)
csv.converters # => [:integer]
csv.convert(proc {|x| x.to_s })
csv.converters
No documentation available

Calls the block with each successive row. The data source must be opened for reading.

Without headers:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.each do |row|
  p row
end

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

With headers:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string, headers: true)
csv.each do |row|
  p row
end

Output:

<CSV::Row "Name":"foo" "Value":"0">
<CSV::Row "Name":"bar" "Value":"1">
<CSV::Row "Name":"baz" "Value":"2">

Raises an exception if the source is not opened for reading:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.close
# Raises IOError (not opened for reading)
csv.each do |row|
  p row
end
An alias for eof?
No documentation available

Returns the limit for field size; used for parsing; see Option field_size_limit:

CSV.new('').field_size_limit # => nil
No documentation available

Returns the value that determines whether all output fields are to be quoted; used for generating; see Option force_quotes:

CSV.new('').force_quotes? # => false
An alias for shift

The block need not return a String object:

csv = CSV.open(path, headers: true)
csv.header_convert {|header, field_info| header.to_sym }
table = csv.read
table.headers # => [:Name, :Value]

If converter_name is given, the block is not called:

csv = CSV.open(path, headers: true)
csv.header_convert(:downcase) {|header, field_info| fail 'Cannot happen' }
table = csv.read
table.headers # => ["name", "value"]

Raises a parse-time exception if converter_name is not the name of a built-in field converter:

csv = CSV.open(path, headers: true)
csv.header_convert(:nosuch)
# Raises NoMethodError (undefined method `arity' for nil:NilClass)
csv.read

Returns an Array containing header converters; used for parsing; see Header Converters:

CSV.new('').header_converters # => []
No documentation available

Returns true if the next row to be read is a header row; false otherwise.

Without headers:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.header_row? # => false

With headers:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string, headers: true)
csv.header_row? # => true
csv.shift # => #<CSV::Row "Name":"foo" "Value":"0">
csv.header_row? # => false

Raises an exception if the source is not opened for reading:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.close
# Raises IOError (not opened for reading)
csv.header_row?

Returns the value that determines whether headers are used; used for parsing; see Option headers:

CSV.new('').headers # => nil

Returns a String showing certain properties of self:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string, headers: true)
s = csv.inspect
s # => "#<CSV io_type:StringIO encoding:UTF-8 lineno:0 col_sep:\",\" row_sep:\"\\n\" quote_char:\"\\\"\" headers:true>"
No documentation available

Returns the value that determines whether illegal input is to be handled; used for parsing; see Option liberal_parsing:

CSV.new('').liberal_parsing? # => false

Returns the line most recently read:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
CSV.open(path) do |csv|
  csv.each do |row|
    p [csv.lineno, csv.line]
  end
end

Output:

[1, "foo,0\n"]
[2, "bar,1\n"]
[3, "baz,2\n"]

Returns the count of the rows parsed or generated.

Parsing:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
CSV.open(path) do |csv|
  csv.each do |row|
    p [csv.lineno, row]
  end
end

Output:

[1, ["foo", "0"]]
[2, ["bar", "1"]]
[3, ["baz", "2"]]

Generating:

CSV.generate do |csv|
  p csv.lineno; csv << ['foo', 0]
  p csv.lineno; csv << ['bar', 1]
  p csv.lineno; csv << ['baz', 2]
end

Output:

0
1
2
No documentation available
No documentation available
No documentation available
No documentation available
No documentation available
No documentation available
An alias for <<

Returns the encoded quote character; used for parsing and writing; see Option quote_char:

CSV.new('').quote_char # => "\""

Returns the encoding of the internal IO object.

Forms the remaining rows from self into:

  • A CSV::Table object, if headers are in use.

  • An Array of Arrays, otherwise.

The data source must be opened for reading.

Without headers:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
csv = CSV.open(path)
csv.read # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

With headers:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
csv = CSV.open(path, headers: true)
csv.read # => #<CSV::Table mode:col_or_row row_count:4>

Raises an exception if the source is not opened for reading:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.close
# Raises IOError (not opened for reading)
csv.read
An alias for shift
An alias for read

Returns the value that determines whether headers are to be returned; used for parsing; see Option return_headers:

CSV.new('').return_headers? # => false

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

Returns the encoded row separator; used for parsing and writing; see Option row_sep:

CSV.new('').row_sep # => "\n"

Returns the next row of data as:

  • An Array if no headers are used.

  • A CSV::Row object if headers are used.

The data source must be opened for reading.

Without headers:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.shift # => ["foo", "0"]
csv.shift # => ["bar", "1"]
csv.shift # => ["baz", "2"]
csv.shift # => nil

With headers:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string, headers: true)
csv.shift # => #<CSV::Row "Name":"foo" "Value":"0">
csv.shift # => #<CSV::Row "Name":"bar" "Value":"1">
csv.shift # => #<CSV::Row "Name":"baz" "Value":"2">
csv.shift # => nil

Raises an exception if the source is not opened for reading:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.close
# Raises IOError (not opened for reading)
csv.shift

Returns the value that determines whether blank lines are to be ignored; used for parsing; see Option skip_blanks:

CSV.new('').skip_blanks? # => false

Returns the Regexp used to identify comment lines; used for parsing; see Option skip_lines:

CSV.new('').skip_lines # => nil
No documentation available
No documentation available
No documentation available

Returns the value that determines whether unconverted fields are to be available; used for parsing; see Option unconverted_fields:

CSV.new('').unconverted_fields? # => nil

Returns the value that determines whether headers are to be written; used for generating; see Option write_headers:

CSV.new('').write_headers? # => nil
No documentation available
No documentation available
No documentation available