Class

A String object holds and manipulates an arbitrary sequence of bytes, typically representing characters. String objects may be created using String::new or as literals.

Because of aliasing issues, users of strings should be aware of the methods that modify the contents of a String object. Typically, methods with names ending in “!'' modify their receiver, while those without a “!'' return a new String. However, there are exceptions, such as String#[]=.

What's Here

First, what's elsewhere. Class String:

Here, class String provides methods that are useful for:

Methods for Creating a String

  • ::new

    Returns a new string.

  • ::try_convert

    Returns a new string created from a given object.

Methods for a Frozen/Unfrozen String

  • #+string

    Returns a string that is not frozen: self, if not frozen; self.dup otherwise.

  • #-string

    Returns a string that is frozen: self, if already frozen; self.freeze otherwise.

  • freeze

    Freezes self, if not already frozen; returns self.

Methods for Querying

Counts

  • length, size

    Returns the count of characters (not bytes).

  • empty?

    Returns true if self.length is zero; false otherwise.

  • bytesize

    Returns the count of bytes.

  • count

    Returns the count of substrings matching given strings.

Substrings

  • #=~

    Returns the index of the first substring that matches a given Regexp or other object; returns nil if no match is found.

  • index

    Returns the index of the first occurrence of a given substring; returns nil if none found.

  • rindex

    Returns the index of the last occurrence of a given substring; returns nil if none found.

  • include?

    Returns true if the string contains a given substring; false otherwise.

  • match

    Returns a MatchData object if the string matches a given Regexp; nil otherwise.

  • match?

    Returns true if the string matches a given Regexp; false otherwise.

  • start_with?

    Returns true if the string begins with any of the given substrings.

  • end_with?

    Returns true if the string ends with any of the given substrings.

Encodings

  • encoding

    Returns the Encoding object that represents the encoding of the string.

  • unicode_normalized?

    Returns true if the string is in Unicode normalized form; false otherwise.

  • valid_encoding?

    Returns true if the string contains only characters that are valid for its encoding.

  • ascii_only?

    Returns true if the string has only ASCII characters; false otherwise.

Other

  • sum

    Returns a basic checksum for the string: the sum of each byte.

  • hash

    Returns the integer hash code.

Methods for Comparing

  • #==, #===

    Returns true if a given other string has the same content as self.

  • eql?

    Returns true if the content is the same as the given other string.

  • #<=>

    Returns -1, 0, or 1 as a given other string is smaller than, equal to, or larger than self.

  • casecmp

    Ignoring case, returns -1, 0, or 1 as a given other string is smaller than, equal to, or larger than self.

  • casecmp?

    Returns true if the string is equal to a given string after Unicode case folding; false otherwise.

Methods for Modifying a String

Each of these methods modifies self.

Insertion

  • insert

    Returns self with a given string inserted at a given offset.

  • <<

    Returns self concatenated with a given string or integer.

Substitution

  • sub!

    Replaces the first substring that matches a given pattern with a given replacement string; returns self if any changes, nil otherwise.

  • gsub!

    Replaces each substring that matches a given pattern with a given replacement string; returns self if any changes, nil otherwise.

  • succ!, next!

    Returns self modified to become its own successor.

  • replace

    Returns self with its entire content replaced by a given string.

  • reverse!

    Returns self with its characters in reverse order.

  • setbyte

    Sets the byte at a given integer offset to a given value; returns the argument.

  • tr!

    Replaces specified characters in self with specified replacement characters; returns self if any changes, nil otherwise.

  • tr_s!

    Replaces specified characters in self with specified replacement characters, removing duplicates from the substrings that were modified; returns self if any changes, nil otherwise.

Casing

  • capitalize!

    Upcases the initial character and downcases all others; returns self if any changes, nil otherwise.

  • downcase!

    Downcases all characters; returns self if any changes, nil otherwise.

  • upcase!

    Upcases all characters; returns self if any changes, nil otherwise.

  • swapcase!

    Upcases each downcase character and downcases each upcase character; returns self if any changes, nil otherwise.

Encoding

  • encode!

    Returns self with all characters transcoded from one given encoding into another.

  • unicode_normalize!

    Unicode-normalizes self; returns self.

  • scrub!

    Replaces each invalid byte with a given character; returns self.

  • force_encoding

    Changes the encoding to a given encoding; returns self.

Deletion

  • clear

    Removes all content, so that self is empty; returns self.

  • slice!, []=

    Removes a substring determined by a given index, start/length, range, regexp, or substring.

  • squeeze!

    Removes contiguous duplicate characters; returns self.

  • delete!

    Removes characters as determined by the intersection of substring arguments.

  • lstrip!

    Removes leading whitespace; returns self if any changes, nil otherwise.

  • rstrip!

    Removes trailing whitespace; returns self if any changes, nil otherwise.

  • strip!

    Removes leading and trailing whitespace; returns self if any changes, nil otherwise.

  • chomp!

    Removes trailing record separator, if found; returns self if any changes, nil otherwise.

  • chop!

    Removes trailing whitespace if found, otherwise removes the last character; returns self if any changes, nil otherwise.

Methods for Converting to New String

Each of these methods returns a new String based on self, often just a modified copy of self.

Extension

  • *

    Returns the concatenation of multiple copies of self,

  • +

    Returns the concatenation of self and a given other string.

  • center

    Returns a copy of self centered between pad substring.

  • concat

    Returns the concatenation of self with given other strings.

  • prepend

    Returns the concatenation of a given other string with self.

  • ljust

    Returns a copy of self of a given length, right-padded with a given other string.

  • rjust

    Returns a copy of self of a given length, left-padded with a given other string.

Encoding

  • b

    Returns a copy of self with ASCII-8BIT encoding.

  • scrub

    Returns a copy of self with each invalid byte replaced with a given character.

  • unicode_normalize

    Returns a copy of self with each character Unicode-normalized.

  • encode

    Returns a copy of self with all characters transcoded from one given encoding into another.

Substitution

  • dump

    Returns a copy of +self with all non-printing characters replaced by xHH notation and all special characters escaped.

  • undump

    Returns a copy of +self with all \xNN notation replace by \uNNNN notation and all escaped characters unescaped.

  • sub

    Returns a copy of self with the first substring matching a given pattern replaced with a given replacement string;.

  • gsub

    Returns a copy of self with each substring that matches a given pattern replaced with a given replacement string.

  • succ, next

    Returns the string that is the successor to self.

  • reverse

    Returns a copy of self with its characters in reverse order.

  • tr

    Returns a copy of self with specified characters replaced with specified replacement characters.

  • tr_s

    Returns a copy of self with specified characters replaced with specified replacement characters, removing duplicates from the substrings that were modified.

  • %

    Returns the string resulting from formatting a given object into self

Casing

  • capitalize

    Returns a copy of self with the first character upcased and all other characters downcased.

  • downcase

    Returns a copy of self with all characters downcased.

  • upcase

    Returns a copy of self with all characters upcased.

  • swapcase

    Returns a copy of self with all upcase characters downcased and all downcase characters upcased.

Deletion

  • delete

    Returns a copy of self with characters removed

  • delete_prefix

    Returns a copy of self with a given prefix removed.

  • delete_suffix

    Returns a copy of self with a given suffix removed.

  • lstrip

    Returns a copy of self with leading whitespace removed.

  • rstrip

    Returns a copy of self with trailing whitespace removed.

  • strip

    Returns a copy of self with leading and trailing whitespace removed.

  • chomp

    Returns a copy of self with a trailing record separator removed, if found.

  • chop

    Returns a copy of self with trailing whitespace or the last character removed.

  • squeeze

    Returns a copy of self with contiguous duplicate characters removed.

  • [], slice

    Returns a substring determined by a given index, start/length, or range, or string.

  • byteslice

    Returns a substring determined by a given index, start/length, or range.

  • chr

    Returns the first character.

Duplication

  • to_s, $to_str

    If self is a subclass of String, returns self copied into a String; otherwise, returns self.

Methods for Converting to Non-String

Each of these methods converts the contents of self to a non-String.

Characters, Bytes, and Clusters

  • bytes

    Returns an array of the bytes in self.

  • chars

    Returns an array of the characters in self.

  • codepoints

    Returns an array of the integer ordinals in self.

  • getbyte

    Returns an integer byte as determined by a given index.

  • grapheme_clusters

    Returns an array of the grapheme clusters in self.

Splitting

  • lines

    Returns an array of the lines in self, as determined by a given record separator.

  • partition

    Returns a 3-element array determined by the first substring that matches a given substring or regexp,

  • rpartition

    Returns a 3-element array determined by the last substring that matches a given substring or regexp,

  • split

    Returns an array of substrings determined by a given delimiter – regexp or string – or, if a block given, passes those substrings to the block.

Matching

  • scan

    Returns an array of substrings matching a given regexp or string, or, if a block given, passes each matching substring to the block.

  • unpack

    Returns an array of substrings extracted from self according to a given format.

  • unpack1

    Returns the first substring extracted from self according to a given format.

Numerics

  • hex

    Returns the integer value of the leading characters, interpreted as hexadecimal digits.

  • oct

    Returns the integer value of the leading characters, interpreted as octal digits.

  • ord

    Returns the integer ordinal of the first character in self.

  • to_i

    Returns the integer value of leading characters, interpreted as an integer.

  • to_f

    Returns the floating-point value of leading characters, interpreted as a floating-point number.

Strings and Symbols

  • inspect

    Returns copy of self, enclosed in double-quotes, with special characters escaped.

  • to_sym, intern

    Returns the symbol corresponding to self.

Methods for Iterating

  • each_byte

    Calls the given block with each successive byte in self.

  • each_char

    Calls the given block with each successive character in self.

  • each_codepoint

    Calls the given block with each successive integer codepoint in self.

  • each_grapheme_cluster

    Calls the given block with each successive grapheme cluster in self.

  • each_line

    Calls the given block with each successive line in self, as determined by a given record separator.

  • upto

    Calls the given block with each string value returned by successive calls to succ.


Class Methods


Returns a new String that is a copy of string.

With no arguments, returns the empty string with the Encoding ASCII-8BIT:

s = String.new
s # => ""
s.encoding # => #<Encoding:ASCII-8BIT>

With the single String argument string, returns a copy of string with the same encoding as string:

s = String.new("Que veut dire \u{e7}a?")
s # => "Que veut dire \u{e7}a?"
s.encoding # => #<Encoding:UTF-8>

Literal strings like "" or here-documents always use script encoding, unlike String.new.

With keyword encoding, returns a copy of str with the specified encoding:

s = String.new(encoding: 'ASCII')
s.encoding # => #<Encoding:US-ASCII>
s = String.new('foo', encoding: 'ASCII')
s.encoding # => #<Encoding:US-ASCII>

Note that these are equivalent:

s0 = String.new('foo', encoding: 'ASCII')
s1 = 'foo'.force_encoding('ASCII')
s0.encoding == s1.encoding # => true

With keyword capacity, returns a copy of str; the given capacity may set the size of the internal buffer, which may affect performance:

String.new(capacity: 1) # => ""
String.new(capacity: 4096) # => ""

The string, encoding, and capacity arguments may all be used together:

String.new('hello', encoding: 'UTF-8', capacity: 25)

If object is a String object, returns object.

Otherwise if object responds to :to_str, calls object.to_str and returns the result.

Returns nil if object does not respond to :to_str

Raises an exception unless object.to_str returns a String object.

Instance Methods


Returns the result of formatting object into the format specification self (see Kernel#sprintf for formatting details):

"%05d" % 123 # => "00123"

If self contains multiple substitutions, object must be an Array or Hash containing the values to be substituted:

"%-5s: %016x" % [ "ID", self.object_id ] # => "ID   : 00002b054ec93168"
"foo = %{foo}" % {foo: 'bar'} # => "foo = bar"
"foo = %{foo}, baz = %{baz}" % {foo: 'bar', baz: 'bat'} # => "foo = bar, baz = bat"

Returns a new String containing integer copies of self:

"Ho! " * 3 # => "Ho! Ho! Ho! "
"Ho! " * 0 # => ""

Returns a new String containing other_string concatenated to self:

"Hello from " + self.to_s # => "Hello from main"

Returns self if self is not frozen.

Otherwise. returns self.dup, which is not frozen.

Returns a frozen, possibly pre-existing copy of the string.

The returned String will be deduplicated as long as it does not have any instance variables set on it.

Returns a new String containing the concatenation of self and object:

s = 'foo'
s << 'bar' # => "foobar"

If object is an Integer, the value is considered a codepoint and converted to a character before concatenation:

s = 'foo'
s << 33 # => "foo!"

Related: String#concat, which takes multiple arguments.

Compares self and other_string, returning:

  • -1 if other_string is larger.

  • 0 if the two are equal.

  • 1 if other_string is smaller.

  • nil if the two are incomparable.

Examples:

'foo' <=> 'foo' # => 0
'foo' <=> 'food' # => -1
'food' <=> 'foo' # => 1
'FOO' <=> 'foo' # => -1
'foo' <=> 'FOO' # => 1
'foo' <=> 1 # => nil

Returns true if object has the same length and content; as self; false otherwise:

s = 'foo'
s == 'foo' # => true
s == 'food' # => false
s == 'FOO' # => false

Returns false if the two strings' encodings are not compatible:

"\u{e4 f6 fc}".encode("ISO-8859-1") == ("\u{c4 d6 dc}") # => false

If object is not an instance of String but responds to to_str, then the two strings are compared using object.==.

Returns the Integer index of the first substring that matches the given regexp, or nil if no match found:

'foo' =~ /f/ # => 0
'foo' =~ /o/ # => 1
'foo' =~ /x/ # => nil

Note: also updates Regexp-related global variables.

If the given object is not a Regexp, returns the value returned by object =~ self.

Note that string =~ regexp is different from regexp =~ string (see Regexp#=~):

number= nil
"no. 9" =~ /(?<number>\d+)/
number # => nil (not assigned)
/(?<number>\d+)/ =~ "no. 9"
number #=> "9"

Returns the substring of self specified by the arguments.

When the single Integer argument index is given, returns the 1-character substring found in self at offset index:

'bar'[2] # => "r"

Counts backward from the end of self if index is negative:

'foo'[-3] # => "f"

Returns nil if index is out of range:

'foo'[3] # => nil
'foo'[-4] # => nil

When the two Integer arguments start and length are given, returns the substring of the given length found in self at offset start:

'foo'[0, 2] # => "fo"
'foo'[0, 0] # => ""

Counts backward from the end of self if start is negative:

'foo'[-2, 2] # => "oo"

Special case: returns a new empty String if start is equal to the length of self:

'foo'[3, 2] # => ""

Returns nil if start is out of range:

'foo'[4, 2] # => nil
'foo'[-4, 2] # => nil

Returns the trailing substring of self if length is large:

'foo'[1, 50] # => "oo"

Returns nil if length is negative:

'foo'[0, -1] # => nil

When the single Range argument range is given, derives start and length values from the given range, and returns values as above:

  • 'foo'[0..1] is equivalent to 'foo'[0, 2].

  • 'foo'[0...1] is equivalent to 'foo'[0, 1].

When the Regexp argument regexp is given, and the capture argument is 0, returns the first matching substring found in self, or nil if none found:

'foo'[/o/] # => "o"
'foo'[/x/] # => nil
s = 'hello there'
s[/[aeiou](.)\1/] # => "ell"
s[/[aeiou](.)\1/, 0] # => "ell"

If argument capture is given and not 0, it should be either an Integer capture group index or a String or Symbol capture group name; the method call returns only the specified capture (see Regexp Capturing):

s = 'hello there'
s[/[aeiou](.)\1/, 1] # => "l"
s[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, "non_vowel"] # => "l"
s[/(?<vowel>[aeiou])(?<non_vowel>[^aeiou])/, :vowel] # => "e"

If an invalid capture group index is given, nil is returned. If an invalid capture group name is given, IndexError is raised.

When the single String argument substring is given, returns the substring from self if found, otherwise nil:

'foo'['oo'] # => "oo"
'foo'['xx'] # => nil

String#slice is an alias for String#[].

Element Assignment—Replaces some or all of the content of str. The portion of the string affected is determined using the same criteria as String#[]. If the replacement string is not the same length as the text it is replacing, the string will be adjusted accordingly. If the regular expression or string is used as the index doesn't match a position in the string, IndexError is raised. If the regular expression form is used, the optional second Integer allows you to specify which portion of the match to replace (effectively using the MatchData indexing rules. The forms that take an Integer will raise an IndexError if the value is out of range; the Range form will raise a RangeError, and the Regexp and String will raise an IndexError on negative match.

Returns true for a string which has only ASCII characters.

"abc".force_encoding("UTF-8").ascii_only?          #=> true
"abc\u{6666}".force_encoding("UTF-8").ascii_only?  #=> false

Returns a copied string whose encoding is ASCII-8BIT.

Returns an array of bytes in str. This is a shorthand for str.each_byte.to_a.

If a block is given, which is a deprecated form, works the same as each_byte.

Returns the count of bytes in self:

"\x80\u3042".bytesize # => 4
"hello".bytesize # => 5

Related: String#length.

Byte Reference—If passed a single Integer, returns a substring of one byte at that position. If passed two Integer objects, returns a substring starting at the offset given by the first, and a length given by the second. If given a Range, a substring containing bytes at offsets given by the range is returned. In all three cases, if an offset is negative, it is counted from the end of str. Returns nil if the initial offset falls outside the string, the length is negative, or the beginning of the range is greater than the end. The encoding of the resulted string keeps original encoding.

"hello".byteslice(1)     #=> "e"
"hello".byteslice(-1)    #=> "o"
"hello".byteslice(1, 2)  #=> "el"
"\x80\u3042".byteslice(1, 3) #=> "\u3042"
"\x03\u3042\xff".byteslice(1..3) #=> "\u3042"

Returns a copy of str with the first character converted to uppercase and the remainder to lowercase.

See String#downcase for meaning of options and use with different encodings.

"hello".capitalize    #=> "Hello"
"HELLO".capitalize    #=> "Hello"
"123ABC".capitalize   #=> "123abc"

Modifies str by converting the first character to uppercase and the remainder to lowercase. Returns nil if no changes are made. There is an exception for modern Georgian (mkhedruli/MTAVRULI), where the result is the same as for String#downcase, to avoid mixed case.

See String#downcase for meaning of options and use with different encodings.

a = "hello"
a.capitalize!   #=> "Hello"
a               #=> "Hello"
a.capitalize!   #=> nil

Compares self and other_string, ignoring case, and returning:

  • -1 if other_string is larger.

  • 0 if the two are equal.

  • 1 if other_string is smaller.

  • nil if the two are incomparable.

Examples:

'foo'.casecmp('foo') # => 0
'foo'.casecmp('food') # => -1
'food'.casecmp('foo') # => 1
'FOO'.casecmp('foo') # => 0
'foo'.casecmp('FOO') # => 0
'foo'.casecmp(1) # => nil

Returns true if self and other_string are equal after Unicode case folding, otherwise false:

'foo'.casecmp?('foo') # => true
'foo'.casecmp?('food') # => false
'food'.casecmp?('foo') # => false
'FOO'.casecmp?('foo') # => true
'foo'.casecmp?('FOO') # => true

Returns nil if the two values are incomparable:

'foo'.casecmp?(1) # => nil

Centers str in width. If width is greater than the length of str, returns a new String of length width with str centered and padded with padstr; otherwise, returns str.

"hello".center(4)         #=> "hello"
"hello".center(20)        #=> "       hello        "
"hello".center(20, '123') #=> "1231231hello12312312"

Returns an array of characters in str. This is a shorthand for str.each_char.to_a.

If a block is given, which is a deprecated form, works the same as each_char.

Returns a new String with the given record separator removed from the end of str (if present). If $/ has not been changed from the default Ruby record separator, then chomp also removes carriage return characters (that is, it will remove \n, \r, and \r\n). If $/ is an empty string, it will remove all trailing newlines from the string.

"hello".chomp                #=> "hello"
"hello\n".chomp              #=> "hello"
"hello\r\n".chomp            #=> "hello"
"hello\n\r".chomp            #=> "hello\n"
"hello\r".chomp              #=> "hello"
"hello \n there".chomp       #=> "hello \n there"
"hello".chomp("llo")         #=> "he"
"hello\r\n\r\n".chomp('')    #=> "hello"
"hello\r\n\r\r\n".chomp('')  #=> "hello\r\n\r"

Modifies str in place as described for String#chomp, returning str, or nil if no modifications were made.

Returns a new String with the last character removed. If the string ends with \r\n, both characters are removed. Applying chop to an empty string returns an empty string. String#chomp is often a safer alternative, as it leaves the string unchanged if it doesn't end in a record separator.

"string\r\n".chop   #=> "string"
"string\n\r".chop   #=> "string\n"
"string\n".chop     #=> "string"
"string".chop       #=> "strin"
"x".chop.chop       #=> ""

Processes str as for String#chop, returning str, or nil if str is the empty string. See also String#chomp!.

Returns a one-character string at the beginning of the string.

a = "abcde"
a.chr    #=> "a"

Makes string empty.

a = "abcde"
a.clear    #=> ""

Returns an array of the Integer ordinals of the characters in str. This is a shorthand for str.each_codepoint.to_a.

If a block is given, which is a deprecated form, works the same as each_codepoint.

Returns a new String containing the concatenation of self and all objects in objects:

s = 'foo'
s.concat('bar', 'baz') # => "foobarbaz"

For each given object object that is an Integer, the value is considered a codepoint and converted to a character before concatenation:

s = 'foo'
s.concat(32, 'bar', 32, 'baz') # => "foo bar baz"

Related: String#<<, which takes a single argument.

Each other_str parameter defines a set of characters to count. The intersection of these sets defines the characters to count in str. Any other_str that starts with a caret ^ is negated. The sequence c1-c2 means all characters between c1 and c2. The backslash character \ can be used to escape ^ or - and is otherwise ignored unless it appears at the end of a sequence or the end of a other_str.

a = "hello world"
a.count "lo"                   #=> 5
a.count "lo", "o"              #=> 2
a.count "hello", "^l"          #=> 4
a.count "ej-m"                 #=> 4

"hello^world".count "\\^aeiou" #=> 4
"hello-world".count "a\\-eo"   #=> 4

c = "hello world\\r\\n"
c.count "\\"                   #=> 2
c.count "\\A"                  #=> 0
c.count "X-\\w"                #=> 3

Returns the string generated by calling crypt(3) standard library function with str and salt_str, in this order, as its arguments. Please do not use this method any longer. It is legacy; provided only for backward compatibility with ruby scripts in earlier days. It is bad to use in contemporary programs for several reasons:

  • Behaviour of C's crypt(3) depends on the OS it is run. The generated string lacks data portability.

  • On some OSes such as Mac OS, crypt(3) never fails (i.e. silently ends up in unexpected results).

  • On some OSes such as Mac OS, crypt(3) is not thread safe.

  • So-called “traditional” usage of crypt(3) is very very very weak. According to its manpage, Linux's traditional crypt(3) output has only 2**56 variations; too easy to brute force today. And this is the default behaviour.

  • In order to make things robust some OSes implement so-called “modular” usage. To go through, you have to do a complex build-up of the salt_str parameter, by hand. Failure in generation of a proper salt string tends not to yield any errors; typos in parameters are normally not detectable.

    • For instance, in the following example, the second invocation of String#crypt is wrong; it has a typo in “round=” (lacks “s”). However the call does not fail and something unexpected is generated.

      "foo".crypt("$5$rounds=1000$salt$") # OK, proper usage
      "foo".crypt("$5$round=1000$salt$")  # Typo not detected
      
  • Even in the “modular” mode, some hash functions are considered archaic and no longer recommended at all; for instance module $1$ is officially abandoned by its author: see phk.freebsd.dk/sagas/md5crypt_eol/ . For another instance module $3$ is considered completely broken: see the manpage of FreeBSD.

  • On some OS such as Mac OS, there is no modular mode. Yet, as written above, crypt(3) on Mac OS never fails. This means even if you build up a proper salt string it generates a traditional DES hash anyways, and there is no way for you to be aware of.

    "foo".crypt("$5$rounds=1000$salt$") # => "$5fNPQMxC5j6."
    

If for some reason you cannot migrate to other secure contemporary password hashing algorithms, install the string-crypt gem and require 'string/crypt' to continue using it.

Returns a copy of str with all characters in the intersection of its arguments deleted. Uses the same rules for building the set of characters as String#count.

"hello".delete "l","lo"        #=> "heo"
"hello".delete "lo"            #=> "he"
"hello".delete "aeiou", "^e"   #=> "hell"
"hello".delete "ej-m"          #=> "ho"

Performs a delete operation in place, returning str, or nil if str was not modified.

Returns a copy of str with leading prefix deleted.

"hello".delete_prefix("hel") #=> "lo"
"hello".delete_prefix("llo") #=> "hello"

Deletes leading prefix from str, returning nil if no change was made.

"hello".delete_prefix!("hel") #=> "lo"
"hello".delete_prefix!("llo") #=> nil

Returns a copy of str with trailing suffix deleted.

"hello".delete_suffix("llo") #=> "he"
"hello".delete_suffix("hel") #=> "hello"

Deletes trailing suffix from str, returning nil if no change was made.

"hello".delete_suffix!("llo") #=> "he"
"hello".delete_suffix!("hel") #=> nil

Returns a copy of str with all uppercase letters replaced with their lowercase counterparts. Which letters exactly are replaced, and by which other letters, depends on the presence or absence of options, and on the encoding of the string.

The meaning of the options is as follows:

No option

Full Unicode case mapping, suitable for most languages (see :turkic and :lithuanian options below for exceptions). Context-dependent case mapping as described in Table 3-14 of the Unicode standard is currently not supported.

:ascii

Only the ASCII region, i.e. the characters “A'' to “Z'' and “a'' to “z'', are affected. This option cannot be combined with any other option.

:turkic

Full Unicode case mapping, adapted for Turkic languages (Turkish, Azerbaijani, …). This means that upper case I is mapped to lower case dotless i, and so on.

:lithuanian

Currently, just full Unicode case mapping. In the future, full Unicode case mapping adapted for Lithuanian (keeping the dot on the lower case i even if there is an accent on top).

:fold

Only available on downcase and downcase!. Unicode case folding, which is more far-reaching than Unicode case mapping. This option currently cannot be combined with any other option (i.e. there is currently no variant for turkic languages).

Please note that several assumptions that are valid for ASCII-only case conversions do not hold for more general case conversions. For example, the length of the result may not be the same as the length of the input (neither in characters nor in bytes), some roundtrip assumptions (e.g. str.downcase == str.upcase.downcase) may not apply, and Unicode normalization (i.e. String#unicode_normalize) is not necessarily maintained by case mapping operations.

Non-ASCII case mapping/folding is currently supported for UTF-8, UTF-16BE/LE, UTF-32BE/LE, and ISO-8859-1~16 Strings/Symbols. This support will be extended to other encodings.

"hEllO".downcase   #=> "hello"

Downcases the contents of str, returning nil if no changes were made.

See String#downcase for meaning of options and use with different encodings.

Returns a quoted version of the string with all non-printing characters replaced by \xHH notation and all special characters escaped.

This method can be used for round-trip: if the resulting new_str is eval'ed, it will produce the original string.

"hello \n ''".dump     #=> "\"hello \\n ''\""
"\f\x00\xff\\\"".dump  #=> "\"\\f\\x00\\xFF\\\\\\\"\""

See also String#undump.

Passes each byte in str to the given block, or returns an enumerator if no block is given.

"hello".each_byte {|c| print c, ' ' }

produces:

104 101 108 108 111

Passes each character in str to the given block, or returns an enumerator if no block is given.

"hello".each_char {|c| print c, ' ' }

produces:

h e l l o

Passes the Integer ordinal of each character in str, also known as a codepoint when applied to Unicode strings to the given block. For encodings other than UTF-8/UTF-16(BE|LE)/UTF-32(BE|LE), values are directly derived from the binary representation of each character.

If no block is given, an enumerator is returned instead.

"hello\u0639".each_codepoint {|c| print c, ' ' }

produces:

104 101 108 108 111 1593

Passes each grapheme cluster in str to the given block, or returns an enumerator if no block is given. Unlike String#each_char, this enumerates by grapheme clusters defined by Unicode Standard Annex #29 unicode.org/reports/tr29/

"a\u0300".each_char.to_a.size #=> 2
"a\u0300".each_grapheme_cluster.to_a.size #=> 1

Splits str using the supplied parameter as the record separator ($/ by default), passing each substring in turn to the supplied block. If a zero-length record separator is supplied, the string is split into paragraphs delimited by multiple successive newlines.

If chomp is true, separator will be removed from the end of each line.

If no block is given, an enumerator is returned instead.

"hello\nworld".each_line {|s| p s}
# prints:
#   "hello\n"
#   "world"

"hello\nworld".each_line('l') {|s| p s}
# prints:
#   "hel"
#   "l"
#   "o\nworl"
#   "d"

"hello\n\n\nworld".each_line('') {|s| p s}
# prints
#   "hello\n\n"
#   "world"

"hello\nworld".each_line(chomp: true) {|s| p s}
# prints:
#   "hello"
#   "world"

"hello\nworld".each_line('l', chomp: true) {|s| p s}
# prints:
#   "he"
#   ""
#   "o\nwor"
#   "d"

Returns true if the length of self is zero, false otherwise:

"hello".empty? # => false
" ".empty? # => false
"".empty? # => true

The first form returns a copy of str transcoded to encoding encoding. The second form returns a copy of str transcoded from src_encoding to dst_encoding. The last form returns a copy of str transcoded to Encoding.default_internal.

By default, the first and second form raise Encoding::UndefinedConversionError for characters that are undefined in the destination encoding, and Encoding::InvalidByteSequenceError for invalid byte sequences in the source encoding. The last form by default does not raise exceptions but uses replacement strings.

The options keyword arguments give details for conversion. The arguments are:

:invalid

If the value is :replace, encode replaces invalid byte sequences in str with the replacement character. The default is to raise the Encoding::InvalidByteSequenceError exception

:undef

If the value is :replace, encode replaces characters which are undefined in the destination encoding with the replacement character. The default is to raise the Encoding::UndefinedConversionError.

:replace

Sets the replacement string to the given value. The default replacement string is “uFFFD” for Unicode encoding forms, and “?” otherwise.

:fallback

Sets the replacement string by the given object for undefined character. The object should be a Hash, a Proc, a Method, or an object which has [] method. Its key is an undefined character encoded in the source encoding of current transcoder. Its value can be any encoding until it can be converted into the destination encoding of the transcoder.

:xml

The value must be :text or :attr. If the value is :text encode replaces undefined characters with their (upper-case hexadecimal) numeric character references. '&', '<', and '>' are converted to “&amp;”, “&lt;”, and “&gt;”, respectively. If the value is :attr, encode also quotes the replacement result (using '“'), and replaces '”' with “&quot;”.

:cr_newline

Replaces LF (“n”) with CR (“r”) if value is true.

:crlf_newline

Replaces LF (“n”) with CRLF (“rn”) if value is true.

:universal_newline

Replaces CRLF (“rn”) and CR (“r”) with LF (“n”) if value is true.

The first form transcodes the contents of str from str.encoding to encoding. The second form transcodes the contents of str from src_encoding to dst_encoding. The options keyword arguments give details for conversion. See String#encode for details. Returns the string even if no changes were made.

Returns the Encoding object that represents the encoding of obj.

Returns true if str ends with one of the suffixes given.

"hello".end_with?("ello")               #=> true

# returns true if one of the +suffixes+ matches.
"hello".end_with?("heaven", "ello")     #=> true
"hello".end_with?("heaven", "paradise") #=> false

Returns true if object has the same length and content; as self; false otherwise:

s = 'foo'
s.eql?('foo') # => true
s.eql?('food') # => false
s.eql?('FOO') # => false

Returns false if the two strings' encodings are not compatible:

"\u{e4 f6 fc}".encode("ISO-8859-1").eql?("\u{c4 d6 dc}") # => false

Changes the encoding to encoding and returns self.

No documentation available

returns the indexth byte as an integer.

Returns an array of grapheme clusters in str. This is a shorthand for str.each_grapheme_cluster.to_a.

If a block is given, which is a deprecated form, works the same as each_grapheme_cluster.

Returns a copy of str with all occurrences of pattern substituted for the second argument. The pattern is typically a Regexp; if given as a String, any regular expression metacharacters it contains will be interpreted literally, e.g. \d will match a backslash followed by 'd', instead of a digit.

If replacement is a String it will be substituted for the matched text. It may contain back-references to the pattern's capture groups of the form \d, where d is a group number, or \k<n>, where n is a group name. Similarly, \&, \', \`, and + correspond to special variables, $&, $', $`, and $+, respectively. (See regexp.rdoc for details.) \0 is the same as \&. \\ is interpreted as an escape, i.e., a single backslash. Note that, within replacement the special match variables, such as $&, will not refer to the current match.

If the second argument is a Hash, and the matched text is one of its keys, the corresponding value is the replacement string.

In the block form, the current match string is passed in as a parameter, and variables such as $1, $2, $`, $&, and $' will be set appropriately. (See regexp.rdoc for details.) The value returned by the block will be substituted for the match on each call.

When neither a block nor a second argument is supplied, an Enumerator is returned.

"hello".gsub(/[aeiou]/, '*')                  #=> "h*ll*"
"hello".gsub(/([aeiou])/, '<\1>')             #=> "h<e>ll<o>"
"hello".gsub(/./) {|s| s.ord.to_s + ' '}      #=> "104 101 108 108 111 "
"hello".gsub(/(?<foo>[aeiou])/, '{\k<foo>}')  #=> "h{e}ll{o}"
'hello'.gsub(/[eo]/, 'e' => 3, 'o' => '*')    #=> "h3ll*"

Note that a string literal consumes backslashes. (See syntax/literals.rdoc for details on string literals.) Back-references are typically preceded by an additional backslash. For example, if you want to write a back-reference \& in replacement with a double-quoted string literal, you need to write: "..\\&..". If you want to write a non-back-reference string \& in replacement, you need first to escape the backslash to prevent this method from interpreting it as a back-reference, and then you need to escape the backslashes again to prevent a string literal from consuming them: "..\\\\&..". You may want to use the block form to avoid a lot of backslashes.

Performs the substitutions of String#gsub in place, returning str, or nil if no substitutions were performed. If no block and no replacement is given, an enumerator is returned instead.

Returns the integer hash value for self. The value is based on the length, content and encoding of self.

Related: Object#hash

Treats leading characters from str as a string of hexadecimal digits (with an optional sign and an optional 0x) and returns the corresponding number. Zero is returned on error.

"0x0a".hex     #=> 10
"-1234".hex    #=> -4660
"0".hex        #=> 0
"wombat".hex   #=> 0

Returns true if str contains the given string or character.

"hello".include? "lo"   #=> true
"hello".include? "ol"   #=> false
"hello".include? ?h     #=> true

Returns the Integer index of the first occurrence of the given substring, or nil if none found:

'foo'.index('f') # => 0
'foo'.index('o') # => 1
'foo'.index('oo') # => 1
'foo'.index('ooo') # => nil

Returns the Integer index of the first match for the given Regexp regexp, or nil if none found:

'foo'.index(/f/) # => 0
'foo'.index(/o/) # => 1
'foo'.index(/oo/) # => 1
'foo'.index(/ooo/) # => nil

Integer argument offset, if given, specifies the position in the string to begin the search:

'foo'.index('o', 1) # => 1
'foo'.index('o', 2) # => 2
'foo'.index('o', 3) # => nil

If offset is negative, counts backward from the end of self:

'foo'.index('o', -1) # => 2
'foo'.index('o', -2) # => 1
'foo'.index('o', -3) # => 1
'foo'.index('o', -4) # => nil

Related: String#rindex

Replaces the contents of str with the corresponding values in other_str.

s = "hello"         #=> "hello"
s.replace "world"   #=> "world"

Inserts the given other_string into self; returns self.

If the Integer index is positive, inserts other_string at offset index:

'foo'.insert(1, 'bar') # => "fbaroo"

If the Integer index is negative, counts backward from the end of self and inserts other_string at offset index+1 (that is, after self[index]):

'foo'.insert(-2, 'bar') # => "fobaro"

Returns a printable version of str, surrounded by quote marks, with special characters escaped.

str = "hello"
str[3] = "\b"
str.inspect       #=> "\"hel\\bo\""

Returns the Symbol corresponding to str, creating the symbol if it did not previously exist. See Symbol#id2name.

"Koala".intern         #=> :Koala
s = 'cat'.to_sym       #=> :cat
s == :cat              #=> true
s = '@cat'.to_sym      #=> :@cat
s == :@cat             #=> true

This can also be used to create symbols that cannot be represented using the :xxx notation.

'cat and dog'.to_sym   #=> :"cat and dog"

Returns whether self's encoding is EUC-JP or not.

Returns whether self's encoding is ISO-2022-JP or not.

Returns whether self's encoding is Shift_JIS or not.

Returns whether self's encoding is UTF-8 or not.

Convert self to to_enc. to_enc and from_enc are given as constants of Kconv or Encoding objects.

Returns the count of characters (not bytes) in self:

"\x80\u3042".length # => 2
"hello".length # => 5

String#size is an alias for String#length.

Related: String#bytesize.

Returns an array of lines in str split using the supplied record separator ($/ by default). This is a shorthand for str.each_line(separator, getline_args).to_a.

If chomp is true, separator will be removed from the end of each line.

"hello\nworld\n".lines              #=> ["hello\n", "world\n"]
"hello  world".lines(' ')           #=> ["hello ", " ", "world"]
"hello\nworld\n".lines(chomp: true) #=> ["hello", "world"]

If a block is given, which is a deprecated form, works the same as each_line.

If integer is greater than the length of str, returns a new String of length integer with str left justified and padded with padstr; otherwise, returns str.

"hello".ljust(4)            #=> "hello"
"hello".ljust(20)           #=> "hello               "
"hello".ljust(20, '1234')   #=> "hello123412341234123"

Returns a copy of the receiver with leading whitespace removed. See also String#rstrip and String#strip.

Refer to String#strip for the definition of whitespace.

"  hello  ".lstrip   #=> "hello  "
"hello".lstrip       #=> "hello"

Removes leading whitespace from the receiver. Returns the altered receiver, or nil if no change was made. See also String#rstrip! and String#strip!.

Refer to String#strip for the definition of whitespace.

"  hello  ".lstrip!  #=> "hello  "
"hello  ".lstrip!    #=> nil
"hello".lstrip!      #=> nil

Returns a Matchdata object (or nil) based on self and the given pattern.

Note: also updates Regexp-related global variables.

  • Computes regexp by converting pattern (if not already a Regexp).

    regexp = Regexp.new(pattern)
    
  • Computes matchdata, which will be either a MatchData object or nil (see Regexp#match):

    matchdata = <tt>regexp.match(self)

With no block given, returns the computed matchdata:

'foo'.match('f') # => #<MatchData "f">
'foo'.match('o') # => #<MatchData "o">
'foo'.match('x') # => nil

If Integer argument offset is given, the search begins at index offset:

'foo'.match('f', 1) # => nil
'foo'.match('o', 1) # => #<MatchData "o">

With a block given, calls the block with the computed matchdata and returns the block's return value:

'foo'.match(/o/) {|matchdata| matchdata } # => #<MatchData "o">
'foo'.match(/x/) {|matchdata| matchdata } # => nil
'foo'.match(/f/, 1) {|matchdata| matchdata } # => nil

Returns true or false based on whether a match is found for self and pattern.

Note: does not update Regexp-related global variables.

Computes regexp by converting pattern (if not already a Regexp).

regexp = Regexp.new(pattern)

Returns true if self+.match(regexp) returns a Matchdata object, false otherwise:

'foo'.match?(/o/) # => true
'foo'.match?('o') # => true
'foo'.match?(/x/) # => false

If Integer argument offset is given, the search begins at index offset:

'foo'.match?('f', 1) # => false
'foo'.match?('o', 1) # => true
An alias for succ
An alias for succ!

Treats leading characters of str as a string of octal digits (with an optional sign) and returns the corresponding number. Returns 0 if the conversion fails.

"123".oct       #=> 83
"-377".oct      #=> -255
"bad".oct       #=> 0
"0377bad".oct   #=> 255

If str starts with 0, radix indicators are honored. See Kernel#Integer.

Returns the Integer ordinal of a one-character string.

"a".ord         #=> 97

Searches sep or pattern (regexp) in the string and returns the part before it, the match, and the part after it. If it is not found, returns two empty strings and str.

"hello".partition("l")         #=> ["he", "l", "lo"]
"hello".partition("x")         #=> ["hello", "", ""]
"hello".partition(/.l/)        #=> ["h", "el", "lo"]

Returns a new String containing the concatenation of all given other_strings and self:

s = 'foo'
s.prepend('bar', 'baz') # => "barbazfoo"

Related: String#concat.

Returns a new string with the characters from str in reverse order.

"stressed".reverse   #=> "desserts"

Reverses str in place.

Returns the Integer index of the last occurrence of the given substring, or nil if none found:

'foo'.rindex('f') # => 0
'foo'.rindex('o') # => 2
'foo'.rindex('oo') # => 1
'foo'.rindex('ooo') # => nil

Returns the Integer index of the last match for the given Regexp regexp, or nil if none found:

'foo'.rindex(/f/) # => 0
'foo'.rindex(/o/) # => 2
'foo'.rindex(/oo/) # => 1
'foo'.rindex(/ooo/) # => nil

Integer argument offset, if given and non-negative, specifies the maximum starting position in the

string to _end_ the search:
 'foo'.rindex('o', 0) # => nil
 'foo'.rindex('o', 1) # => 1
 'foo'.rindex('o', 2) # => 2
 'foo'.rindex('o', 3) # => 2

If offset is a negative Integer, the maximum starting position in the string to end the search is the sum of the string's length and offset:

'foo'.rindex('o', -1) # => 2
'foo'.rindex('o', -2) # => 1
'foo'.rindex('o', -3) # => nil
'foo'.rindex('o', -4) # => nil

Related: String#index

If integer is greater than the length of str, returns a new String of length integer with str right justified and padded with padstr; otherwise, returns str.

"hello".rjust(4)            #=> "hello"
"hello".rjust(20)           #=> "               hello"
"hello".rjust(20, '1234')   #=> "123412341234123hello"

Searches sep or pattern (regexp) in the string from the end of the string, and returns the part before it, the match, and the part after it. If it is not found, returns two empty strings and str.

"hello".rpartition("l")         #=> ["hel", "l", "o"]
"hello".rpartition("x")         #=> ["", "", "hello"]
"hello".rpartition(/.l/)        #=> ["he", "ll", "o"]

Returns a copy of the receiver with trailing whitespace removed. See also String#lstrip and String#strip.

Refer to String#strip for the definition of whitespace.

"  hello  ".rstrip   #=> "  hello"
"hello".rstrip       #=> "hello"

Removes trailing whitespace from the receiver. Returns the altered receiver, or nil if no change was made. See also String#lstrip! and String#strip!.

Refer to String#strip for the definition of whitespace.

"  hello  ".rstrip!  #=> "  hello"
"  hello".rstrip!    #=> nil
"hello".rstrip!      #=> nil

Both forms iterate through str, matching the pattern (which may be a Regexp or a String). For each match, a result is generated and either added to the result array or passed to the block. If the pattern contains no groups, each individual result consists of the matched string, $&. If the pattern contains groups, each individual result is itself an array containing one entry per group.

a = "cruel world"
a.scan(/\w+/)        #=> ["cruel", "world"]
a.scan(/.../)        #=> ["cru", "el ", "wor"]
a.scan(/(...)/)      #=> [["cru"], ["el "], ["wor"]]
a.scan(/(..)(..)/)   #=> [["cr", "ue"], ["l ", "wo"]]

And the block form:

a.scan(/\w+/) {|w| print "<<#{w}>> " }
print "\n"
a.scan(/(.)(.)/) {|x,y| print y, x }
print "\n"

produces:

<<cruel>> <<world>>
rceu lowlr

If the string is invalid byte sequence then replace invalid bytes with given replacement character, else returns self. If block is given, replace invalid bytes with returned value of the block.

"abc\u3042\x81".scrub #=> "abc\u3042\uFFFD"
"abc\u3042\x81".scrub("*") #=> "abc\u3042*"
"abc\u3042\xE3\x80".scrub{|bytes| '<'+bytes.unpack('H*')[0]+'>' } #=> "abc\u3042<e380>"

If the string is invalid byte sequence then replace invalid bytes with given replacement character, else returns self. If block is given, replace invalid bytes with returned value of the block.

"abc\u3042\x81".scrub! #=> "abc\u3042\uFFFD"
"abc\u3042\x81".scrub!("*") #=> "abc\u3042*"
"abc\u3042\xE3\x80".scrub!{|bytes| '<'+bytes.unpack('H*')[0]+'>' } #=> "abc\u3042<e380>"

modifies the indexth byte as integer.

Escapes str so that it can be safely used in a Bourne shell command line.

See Shellwords.shellescape for details.

Splits str into an array of tokens in the same way the UNIX Bourne shell does.

See Shellwords.shellsplit for details.

An alias for length
An alias for []

Deletes the specified portion from str, and returns the portion deleted.

string = "this is a string"
string.slice!(2)        #=> "i"
string.slice!(3..6)     #=> " is "
string.slice!(/s.*t/)   #=> "sa st"
string.slice!("r")      #=> "r"
string                  #=> "thing"

Divides str into substrings based on a delimiter, returning an array of these substrings.

If pattern is a String, then its contents are used as the delimiter when splitting str. If pattern is a single space, str is split on whitespace, with leading and trailing whitespace and runs of contiguous whitespace characters ignored.

If pattern is a Regexp, str is divided where the pattern matches. Whenever the pattern matches a zero-length string, str is split into individual characters. If pattern contains groups, the respective matches will be returned in the array as well.

If pattern is nil, the value of $; is used. If $; is nil (which is the default), str is split on whitespace as if ' ' were specified.

If the limit parameter is omitted, trailing null fields are suppressed. If limit is a positive number, at most that number of split substrings will be returned (captured groups will be returned as well, but are not counted towards the limit). If limit is 1, the entire string is returned as the only entry in an array. If negative, there is no limit to the number of fields returned, and trailing null fields are not suppressed.

When the input str is empty an empty Array is returned as the string is considered to have no fields to split.

" now's  the time ".split       #=> ["now's", "the", "time"]
" now's  the time ".split(' ')  #=> ["now's", "the", "time"]
" now's  the time".split(/ /)   #=> ["", "now's", "", "the", "time"]
"1, 2.34,56, 7".split(%r{,\s*}) #=> ["1", "2.34", "56", "7"]
"hello".split(//)               #=> ["h", "e", "l", "l", "o"]
"hello".split(//, 3)            #=> ["h", "e", "llo"]
"hi mom".split(%r{\s*})         #=> ["h", "i", "m", "o", "m"]

"mellow yellow".split("ello")   #=> ["m", "w y", "w"]
"1,2,,3,4,,".split(',')         #=> ["1", "2", "", "3", "4"]
"1,2,,3,4,,".split(',', 4)      #=> ["1", "2", "", "3,4,,"]
"1,2,,3,4,,".split(',', -4)     #=> ["1", "2", "", "3", "4", "", ""]

"1:2:3".split(/(:)()()/, 2)     #=> ["1", ":", "", "", "2:3"]

"".split(',', -1)               #=> []

If a block is given, invoke the block with each split substring.

Builds a set of characters from the other_str parameter(s) using the procedure described for String#count. Returns a new string where runs of the same character that occur in this set are replaced by a single character. If no arguments are given, all runs of identical characters are replaced by a single character.

"yellow moon".squeeze                  #=> "yelow mon"
"  now   is  the".squeeze(" ")         #=> " now is the"
"putters shoot balls".squeeze("m-z")   #=> "puters shot balls"

Squeezes str in place, returning either str, or nil if no changes were made.

Returns true if str starts with one of the prefixes given. Each of the prefixes should be a String or a Regexp.

"hello".start_with?("hell")               #=> true
"hello".start_with?(/H/i)                 #=> true

# returns true if one of the prefixes matches.
"hello".start_with?("heaven", "hell")     #=> true
"hello".start_with?("heaven", "paradise") #=> false

Returns a copy of the receiver with leading and trailing whitespace removed.

Whitespace is defined as any of the following characters: null, horizontal tab, line feed, vertical tab, form feed, carriage return, space.

"    hello    ".strip   #=> "hello"
"\tgoodbye\r\n".strip   #=> "goodbye"
"\x00\t\n\v\f\r ".strip #=> ""
"hello".strip           #=> "hello"

Removes leading and trailing whitespace from the receiver. Returns the altered receiver, or nil if there was no change.

Refer to String#strip for the definition of whitespace.

"  hello  ".strip!  #=> "hello"
"hello".strip!      #=> nil

Returns a copy of str with the first occurrence of pattern replaced by the second argument. The pattern is typically a Regexp; if given as a String, any regular expression metacharacters it contains will be interpreted literally, e.g. \d will match a backslash followed by 'd', instead of a digit.

If replacement is a String it will be substituted for the matched text. It may contain back-references to the pattern's capture groups of the form \d, where d is a group number, or \k<n>, where n is a group name. Similarly, \&, \', \`, and + correspond to special variables, $&, $', $`, and $+, respectively. (See regexp.rdoc for details.) \0 is the same as \&. \\ is interpreted as an escape, i.e., a single backslash. Note that, within replacement the special match variables, such as $&, will not refer to the current match.

If the second argument is a Hash, and the matched text is one of its keys, the corresponding value is the replacement string.

In the block form, the current match string is passed in as a parameter, and variables such as $1, $2, $`, $&, and $' will be set appropriately. (See regexp.rdoc for details.) The value returned by the block will be substituted for the match on each call.

"hello".sub(/[aeiou]/, '*')                  #=> "h*llo"
"hello".sub(/([aeiou])/, '<\1>')             #=> "h<e>llo"
"hello".sub(/./) {|s| s.ord.to_s + ' ' }     #=> "104 ello"
"hello".sub(/(?<foo>[aeiou])/, '*\k<foo>*')  #=> "h*e*llo"
'Is SHELL your preferred shell?'.sub(/[[:upper:]]{2,}/, ENV)
 #=> "Is /bin/bash your preferred shell?"

Note that a string literal consumes backslashes. (See syntax/literals.rdoc for details about string literals.) Back-references are typically preceded by an additional backslash. For example, if you want to write a back-reference \& in replacement with a double-quoted string literal, you need to write: "..\\&..". If you want to write a non-back-reference string \& in replacement, you need first to escape the backslash to prevent this method from interpreting it as a back-reference, and then you need to escape the backslashes again to prevent a string literal from consuming them: "..\\\\&..". You may want to use the block form to avoid a lot of backslashes.

Performs the same substitution as String#sub in-place.

Returns str if a substitution was performed or nil if no substitution was performed.

Returns the successor to self. The successor is calculated by incrementing characters.

The first character to be incremented is the rightmost alphanumeric: or, if no alphanumerics, the rightmost character:

'THX1138'.succ # => "THX1139"
'<<koala>>'.succ # => "<<koalb>>"
'***'.succ # => '**+'

The successor to a digit is another digit, “carrying” to the next-left character for a “rollover” from 9 to 0, and prepending another digit if necessary:

'00'.succ # => "01"
'09'.succ # => "10"
'99'.succ # => "100"

The successor to a letter is another letter of the same case, carrying to the next-left character for a rollover, and prepending another same-case letter if necessary:

'aa'.succ # => "ab"
'az'.succ # => "ba"
'zz'.succ # => "aaa"
'AA'.succ # => "AB"
'AZ'.succ # => "BA"
'ZZ'.succ # => "AAA"

The successor to a non-alphanumeric character is the next character in the underlying character set's collating sequence, carrying to the next-left character for a rollover, and prepending another character if necessary:

s = 0.chr * 3
s # => "\x00\x00\x00"
s.succ # => "\x00\x00\x01"
s = 255.chr * 3
s # => "\xFF\xFF\xFF"
s.succ # => "\x01\x00\x00\x00"

Carrying can occur between and among mixtures of alphanumeric characters:

s = 'zz99zz99'
s.succ # => "aaa00aa00"
s = '99zz99zz'
s.succ # => "100aa00aa"

The successor to an empty String is a new empty String:

''.succ # => ""

String#next is an alias for String#succ.

Equivalent to String#succ, but modifies self in place; returns self.

String#next! is an alias for String#succ!.

Returns a basic n-bit checksum of the characters in str, where n is the optional Integer parameter, defaulting to 16. The result is simply the sum of the binary value of each byte in str modulo 2**n - 1. This is not a particularly good checksum.

Returns a copy of str with uppercase alphabetic characters converted to lowercase and lowercase characters converted to uppercase.

See String#downcase for meaning of options and use with different encodings.

"Hello".swapcase          #=> "hELLO"
"cYbEr_PuNk11".swapcase   #=> "CyBeR_pUnK11"

Equivalent to String#swapcase, but modifies the receiver in place, returning str, or nil if no changes were made.

See String#downcase for meaning of options and use with different encodings.

Returns a complex which denotes the string form. The parser ignores leading whitespaces and trailing garbage. Any digit sequences can be separated by an underscore. Returns zero for null or garbage string.

'9'.to_c           #=> (9+0i)
'2.5'.to_c         #=> (2.5+0i)
'2.5/1'.to_c       #=> ((5/2)+0i)
'-3/2'.to_c        #=> ((-3/2)+0i)
'-i'.to_c          #=> (0-1i)
'45i'.to_c         #=> (0+45i)
'3-4i'.to_c        #=> (3-4i)
'-4e2-4e-2i'.to_c  #=> (-400.0-0.04i)
'-0.0-0.0i'.to_c   #=> (-0.0-0.0i)
'1/2+3/4i'.to_c    #=> ((1/2)+(3/4)*i)
'ruby'.to_c        #=> (0+0i)

See Kernel.Complex.

Returns the result of interpreting leading characters in str as a BigDecimal.

require 'bigdecimal'
require 'bigdecimal/util'

"0.5".to_d             # => 0.5e0
"123.45e1".to_d        # => 0.12345e4
"45.67 degrees".to_d   # => 0.4567e2

See also BigDecimal::new.

Returns the result of interpreting leading characters in str as a floating point number. Extraneous characters past the end of a valid number are ignored. If there is not a valid number at the start of str, 0.0 is returned. This method never raises an exception.

"123.45e1".to_f        #=> 1234.5
"45.67 degrees".to_f   #=> 45.67
"thx1138".to_f         #=> 0.0

Returns the result of interpreting leading characters in str as an integer base base (between 2 and 36). Extraneous characters past the end of a valid number are ignored. If there is not a valid number at the start of str, 0 is returned. This method never raises an exception when base is valid.

"12345".to_i             #=> 12345
"99 red balloons".to_i   #=> 99
"0a".to_i                #=> 0
"0a".to_i(16)            #=> 10
"hello".to_i             #=> 0
"1100101".to_i(2)        #=> 101
"1100101".to_i(8)        #=> 294977
"1100101".to_i(10)       #=> 1100101
"1100101".to_i(16)       #=> 17826049

Returns the result of interpreting leading characters in str as a rational. Leading whitespace and extraneous characters past the end of a valid number are ignored. Digit sequences can be separated by an underscore. If there is not a valid number at the start of str, zero is returned. This method never raises an exception.

'  2  '.to_r       #=> (2/1)
'300/2'.to_r       #=> (150/1)
'-9.2'.to_r        #=> (-46/5)
'-9.2e2'.to_r      #=> (-920/1)
'1_234_567'.to_r   #=> (1234567/1)
'21 June 09'.to_r  #=> (21/1)
'21/06/09'.to_r    #=> (7/2)
'BWV 1079'.to_r    #=> (0/1)

NOTE: “0.3”.to_r isn't the same as 0.3.to_r. The former is equivalent to “3/10”.to_r, but the latter isn't so.

"0.3".to_r == 3/10r  #=> true
0.3.to_r   == 3/10r  #=> false

See also Kernel#Rational.

Returns self.

If called on a subclass of String, converts the receiver to a String object.

An alias for to_s

Convert self to EUC-JP

Convert self to ISO-2022-JP

Convert self to locale encoding

Convert self to Shift_JIS

Convert self to UTF-16

Convert self to UTF-32

Convert self to UTF-8

Returns a copy of str with the characters in from_str replaced by the corresponding characters in to_str. If to_str is shorter than from_str, it is padded with its last character in order to maintain the correspondence.

"hello".tr('el', 'ip')      #=> "hippo"
"hello".tr('aeiou', '*')    #=> "h*ll*"
"hello".tr('aeiou', 'AA*')  #=> "hAll*"

Both strings may use the c1-c2 notation to denote ranges of characters, and from_str may start with a ^, which denotes all characters except those listed.

"hello".tr('a-y', 'b-z')    #=> "ifmmp"
"hello".tr('^aeiou', '*')   #=> "*e**o"

The backslash character \ can be used to escape ^ or - and is otherwise ignored unless it appears at the end of a range or the end of the from_str or to_str:

"hello^world".tr("\\^aeiou", "*") #=> "h*ll**w*rld"
"hello-world".tr("a\\-eo", "*")   #=> "h*ll**w*rld"

"hello\r\nworld".tr("\r", "")   #=> "hello\nworld"
"hello\r\nworld".tr("\\r", "")  #=> "hello\r\nwold"
"hello\r\nworld".tr("\\\r", "") #=> "hello\nworld"

"X['\\b']".tr("X\\", "")   #=> "['b']"
"X['\\b']".tr("X-\\]", "") #=> "'b'"

Translates str in place, using the same rules as String#tr. Returns str, or nil if no changes were made.

Processes a copy of str as described under String#tr, then removes duplicate characters in regions that were affected by the translation.

"hello".tr_s('l', 'r')     #=> "hero"
"hello".tr_s('el', '*')    #=> "h*o"
"hello".tr_s('el', 'hx')   #=> "hhxo"

Performs String#tr_s processing on str in place, returning str, or nil if no changes were made.

Returns an unescaped version of the string. This does the inverse of String#dump.

"\"hello \\n ''\"".undump #=> "hello \n ''"

Unicode Normalization—Returns a normalized form of str, using Unicode normalizations NFC, NFD, NFKC, or NFKD. The normalization form used is determined by form, which can be any of the four values :nfc, :nfd, :nfkc, or :nfkd. The default is :nfc.

If the string is not in a Unicode Encoding, then an Exception is raised. In this context, 'Unicode Encoding' means any of UTF-8, UTF-16BE/LE, and UTF-32BE/LE, as well as GB18030, UCS_2BE, and UCS_4BE. Anything other than UTF-8 is implemented by converting to UTF-8, which makes it slower than UTF-8.

"a\u0300".unicode_normalize        #=> "\u00E0"
"a\u0300".unicode_normalize(:nfc)  #=> "\u00E0"
"\u00E0".unicode_normalize(:nfd)   #=> "a\u0300"
"\xE0".force_encoding('ISO-8859-1').unicode_normalize(:nfd)
                                   #=> Encoding::CompatibilityError raised

Destructive version of String#unicode_normalize, doing Unicode normalization in place.

Checks whether str is in Unicode normalization form form, which can be any of the four values :nfc, :nfd, :nfkc, or :nfkd. The default is :nfc.

If the string is not in a Unicode Encoding, then an Exception is raised. For details, see String#unicode_normalize.

"a\u0300".unicode_normalized?        #=> false
"a\u0300".unicode_normalized?(:nfd)  #=> true
"\u00E0".unicode_normalized?         #=> true
"\u00E0".unicode_normalized?(:nfd)   #=> false
"\xE0".force_encoding('ISO-8859-1').unicode_normalized?
                                     #=> Encoding::CompatibilityError raised

Decodes str (which may contain binary data) according to the format string, returning an array of each value extracted. The format string consists of a sequence of single-character directives, summarized in the table at the end of this entry. Each directive may be followed by a number, indicating the number of times to repeat with this directive. An asterisk (“*'') will use up all remaining elements. The directives sSiIlL may each be followed by an underscore (“_'') or exclamation mark (“!'') to use the underlying platform's native size for the specified type; otherwise, it uses a platform-independent consistent size. Spaces are ignored in the format string. See also String#unpack1, Array#pack.

"abc \0\0abc \0\0".unpack('A6Z6')   #=> ["abc", "abc "]
"abc \0\0".unpack('a3a3')           #=> ["abc", " \000\000"]
"abc \0abc \0".unpack('Z*Z*')       #=> ["abc ", "abc "]
"aa".unpack('b8B8')                 #=> ["10000110", "01100001"]
"aaa".unpack('h2H2c')               #=> ["16", "61", 97]
"\xfe\xff\xfe\xff".unpack('sS')     #=> [-2, 65534]
"now=20is".unpack('M*')             #=> ["now is"]
"whole".unpack('xax2aX2aX1aX2a')    #=> ["h", "e", "l", "l", "o"]

This table summarizes the various formats and the Ruby classes returned by each.

Integer       |         |
Directive     | Returns | Meaning
------------------------------------------------------------------
C             | Integer | 8-bit unsigned (unsigned char)
S             | Integer | 16-bit unsigned, native endian (uint16_t)
L             | Integer | 32-bit unsigned, native endian (uint32_t)
Q             | Integer | 64-bit unsigned, native endian (uint64_t)
J             | Integer | pointer width unsigned, native endian (uintptr_t)
              |         |
c             | Integer | 8-bit signed (signed char)
s             | Integer | 16-bit signed, native endian (int16_t)
l             | Integer | 32-bit signed, native endian (int32_t)
q             | Integer | 64-bit signed, native endian (int64_t)
j             | Integer | pointer width signed, native endian (intptr_t)
              |         |
S_ S!         | Integer | unsigned short, native endian
I I_ I!       | Integer | unsigned int, native endian
L_ L!         | Integer | unsigned long, native endian
Q_ Q!         | Integer | unsigned long long, native endian (ArgumentError
              |         | if the platform has no long long type.)
J!            | Integer | uintptr_t, native endian (same with J)
              |         |
s_ s!         | Integer | signed short, native endian
i i_ i!       | Integer | signed int, native endian
l_ l!         | Integer | signed long, native endian
q_ q!         | Integer | signed long long, native endian (ArgumentError
              |         | if the platform has no long long type.)
j!            | Integer | intptr_t, native endian (same with j)
              |         |
S> s> S!> s!> | Integer | same as the directives without ">" except
L> l> L!> l!> |         | big endian
I!> i!>       |         |
Q> q> Q!> q!> |         | "S>" is the same as "n"
J> j> J!> j!> |         | "L>" is the same as "N"
              |         |
S< s< S!< s!< | Integer | same as the directives without "<" except
L< l< L!< l!< |         | little endian
I!< i!<       |         |
Q< q< Q!< q!< |         | "S<" is the same as "v"
J< j< J!< j!< |         | "L<" is the same as "V"
              |         |
n             | Integer | 16-bit unsigned, network (big-endian) byte order
N             | Integer | 32-bit unsigned, network (big-endian) byte order
v             | Integer | 16-bit unsigned, VAX (little-endian) byte order
V             | Integer | 32-bit unsigned, VAX (little-endian) byte order
              |         |
U             | Integer | UTF-8 character
w             | Integer | BER-compressed integer (see Array#pack)

Float        |         |
Directive    | Returns | Meaning
-----------------------------------------------------------------
D d          | Float   | double-precision, native format
F f          | Float   | single-precision, native format
E            | Float   | double-precision, little-endian byte order
e            | Float   | single-precision, little-endian byte order
G            | Float   | double-precision, network (big-endian) byte order
g            | Float   | single-precision, network (big-endian) byte order

String       |         |
Directive    | Returns | Meaning
-----------------------------------------------------------------
A            | String  | arbitrary binary string (remove trailing nulls and ASCII spaces)
a            | String  | arbitrary binary string
Z            | String  | null-terminated string
B            | String  | bit string (MSB first)
b            | String  | bit string (LSB first)
H            | String  | hex string (high nibble first)
h            | String  | hex string (low nibble first)
u            | String  | UU-encoded string
M            | String  | quoted-printable, MIME encoding (see RFC2045)
m            | String  | base64 encoded string (RFC 2045) (default)
             |         | base64 encoded string (RFC 4648) if followed by 0
P            | String  | pointer to a structure (fixed-length string)
p            | String  | pointer to a null-terminated string

Misc.        |         |
Directive    | Returns | Meaning
-----------------------------------------------------------------
@            | ---     | skip to the offset given by the length argument
X            | ---     | skip backward one byte
x            | ---     | skip forward one byte

HISTORY

  • J, J! j, and j! are available since Ruby 2.3.

  • Q_, Q!, q_, and q! are available since Ruby 2.1.

  • I!<, i!<, I!>, and i!> are available since Ruby 1.9.3.

Decodes str (which may contain binary data) according to the format string, returning the first value extracted. See also String#unpack, Array#pack.

Contrast with String#unpack:

"abc \0\0abc \0\0".unpack('A6Z6')   #=> ["abc", "abc "]
"abc \0\0abc \0\0".unpack1('A6Z6')  #=> "abc"

In that case data would be lost but often it's the case that the array only holds one value, especially when unpacking binary data. For instance:

“xffx00x00x00”.unpack(“l”) #=> [255] “xffx00x00x00”.unpack1(“l”) #=> 255

Thus unpack1 is convenient, makes clear the intention and signals the expected return value to those reading the code.