class String

Overview

A String represents an immutable sequence of UTF-8 characters.

A String is typically created with a string literal, enclosing UTF-8 characters in double quotes:

"hello world"

A backslash can be used to denote some characters inside the string:

"\"" # double quote
"\\" # backslash
"\e" # escape
"\f" # form feed
"\n" # newline
"\r" # carriage return
"\t" # tab
"\v" # vertical tab

You can use a backslash followed by an u and four hexadecimal characters to denote a unicode codepoint written:

"\u0041" # == "A"

Or you can use curly braces and specify up to six hexadecimal numbers (0 to 10FFFF):

"\u{41}" # == "A"

A string can span multiple lines:

"hello
      world" # same as "hello\n      world"

Note that in the above example trailing and leading spaces, as well as newlines, end up in the resulting string. To avoid this, you can split a string into multiple lines by joining multiple literals with a backslash:

"hello " \
"world, " \
"no newlines" # same as "hello world, no newlines"

Alternatively, a backslash followed by a newline can be inserted inside the string literal:

"hello \
     world, \
     no newlines" # same as "hello world, no newlines"

In this case, leading whitespace is not included in the resulting string.

If you need to write a string that has many double quotes, parentheses, or similar characters, you can use alternative literals:

# Supports double quotes and nested parentheses
%(hello ("world")) # same as "hello (\"world\")"

# Supports double quotes and nested brackets
%[hello ["world"]] # same as "hello [\"world\"]"

# Supports double quotes and nested curlies
%{hello {"world"}} # same as "hello {\"world\"}"

# Supports double quotes and nested angles
%<hello <"world">> # same as "hello <\"world\">"

To create a String with embedded expressions, you can use string interpolation:

a = 1
b = 2
"sum = #{a + b}" # "sum = 3"

This ends up invoking Object#to_s(IO) on each expression enclosed by #{...}.

If you need to dynamically build a string, use String#build or IO::Memory.

Non UTF-8 valid strings

String might end up being conformed of bytes which are an invalid byte sequence according to UTF-8. This can happen if the string is created via one of the constructors that accept bytes, or when getting a string from String.build or IO::Memory. No exception will be raised, but invalid byte sequences, when asked as chars, will use the unicode replacement char (value 0xFFFD). For example:

# here 255 is not a valid byte value in the UTF-8 encoding
string = String.new(Bytes[255, 97])
string.valid_encoding? # => false

# The first char here is the unicode replacement char
string.chars # => ['�', 'a']

One can also create strings with specific byte value in them by using octal and hexadecimal escape sequences:

# Octal escape sequences
"\101" # # => "A"
"\12"  # # => "\n"
"\1"   # string with one character with code point 1
"\377" # string with one byte with value 255

# Hexadecimal escape sequences
"\x45" # # => "A"
"\xFF" # string with one byte with value 255

The reason for allowing strings that don't have a valid UTF-8 sequence is that the world is full of content that isn't properly encoded, and having a program raise an exception or stop because of this is not good. It's better if programs are more resilient, but show a replacement character when there's an error in incoming data.

Included Modules

Defined in:

Class Method Summary

Instance Method Summary

Instance methods inherited from module Comparable(self)

<(other : T) <, <=(other : T) <=, <=>(other : T) <=>, ==(other : T) ==, >(other : T) >, >=(other : T) >=

Instance methods inherited from class Reference

==(other : self)
==(other) ==, dup dup, hash hash, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference)
same?(other : Nil) same?, to_s(io : IO) : Nil to_s

Class methods inherited from class Reference

new new

Instance methods inherited from class Object

!=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other) ===, =~(other) =~, class class, dup dup, hash hash, inspect(io : IO)
inspect inspect, itself itself, not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, tap(&block) tap, to_json(io : IO)
to_json to_json, to_pretty_json(indent : String = " ")
to_pretty_json(io : IO, indent : String = " ") to_pretty_json, to_s
to_s(io : IO) to_s, to_yaml(io : IO)
to_yaml to_yaml, try(&block) try

Class methods inherited from class Object

from_json(string_or_io, root : String) : self
from_json(string_or_io) : self from_json, from_yaml(string_or_io) : self from_yaml

Class Method Detail

def self.build(capacity = 64, &block) : self #

Builds a String by creating a String::Builder with the given initial capacity, yielding it to the block and finally getting a String out of it. The String::Builder automatically resizes as needed.

str = String.build do |str|
  str << "hello "
  str << 1
end
str # => "hello 1"

def self.new(bytes : Bytes, encoding : String, invalid : Symbol? = nil) : String #

Creates a new String from the given bytes, which are encoded in the given encoding.

The invalid argument can be:

  • nil: an exception is raised on invalid byte sequences
  • :skip: invalid byte sequences are ignored
slice = Slice.new(2, 0_u8)
slice[0] = 186_u8
slice[1] = 195_u8
String.new(slice, "GB2312") # => "好"

def self.new(chars : Pointer(UInt8), bytesize, size = 0) #

Creates a new String from a pointer, indicating its bytesize count and, optionally, the UTF-8 codepoints count (size). Bytes will be copied from the pointer.

If the given size is zero, the amount of UTF-8 codepoints will be lazily computed when needed.

ptr = Pointer.malloc(4) { |i| ('a'.ord + i).to_u8 }
String.new(ptr, 2) # => "ab"

def self.new(slice : Bytes) #

Creates a String from the given slice. Bytes will be copied from the slice.

This method is always safe to call, and the resulting string will have the contents and size of the slice.

slice = Slice.new(4) { |i| ('a'.ord + i).to_u8 }
String.new(slice) # => "abcd"

def self.new(chars : Pointer(UInt8)) #

Creates a String from a pointer. Bytes will be copied from the pointer.

This method is unsafe: the pointer must point to data that eventually contains a zero byte that indicates the ends of the string. Otherwise, the result of this method is undefined and might cause a segmentation fault.

This method is typically used in C bindings, where you get a char* from a library and the library guarantees that this pointer eventually has an ending zero byte.

ptr = Pointer.malloc(5) { |i| i == 4 ? 0_u8 : ('a'.ord + i).to_u8 }
String.new(ptr) # => "abcd"

def self.new(capacity : Int, &block) #

Creates a new String by allocating a buffer (Pointer(UInt8)) with the given capacity, then yielding that buffer. The block must return a tuple with the bytesize and size (UTF-8 codepoints count) of the String. If the returned size is zero, the UTF-8 codepoints count will be lazily computed.

The bytesize returned by the block must be less than or equal to the capacity given to this String, otherwise ArgumentError is raised.

If you need to build a String where the maximum capacity is unknown, use String#build.

str = String.new(4) do |buffer|
  buffer[0] = 'a'.ord.to_u8
  buffer[1] = 'b'.ord.to_u8
  {2, 2}
end
str # => "ab"

def self.new(pull : JSON::PullParser) #

def self.new(pull : YAML::PullParser) #

Instance Method Detail

def %(other) #

Interpolates other into the string using Kernel#sprintf.

"Party like it's %d!!!" % 1999 # => "Party like it's 1999!!!"

def *(times : Int) #

Makes a new String by adding str to itself times times.

"Developers! " * 4
# => "Developers! Developers! Developers! Developers!"

def +(other : self) #

Concatenates str and other.

"abc" + "def" # => "abcdef"
"abc" + 'd'   # => "abcd"

def +(char : Char) #

Concatenates str and other.

"abc" + "def" # => "abcdef"
"abc" + 'd'   # => "abcd"

def <=>(other : self) #

Compares this string with other, returning -1, 0 or +1 depending on whether this string is less, equal or greater than other.

Comparison is done byte-per-byte: if a byte is less then the other corresponding byte, -1 is returned and so on.

If the strings are of different lengths, and the strings are equal when compared up to the shortest length, then the longer string is considered greater than the shorter one.

"abcdef" <=> "abcde"   # => 1
"abcdef" <=> "abcdef"  # => 0
"abcdef" <=> "abcdefg" # => -1
"abcdef" <=> "ABCDEF"  # => 1

def ==(other : self) #

def =~(other) #

Tests whether str matches regex. If successful, it returns the position of the first match. If unsuccessful, it returns nil.

If the argument isn't a Regex, it returns nil.

"Haystack" =~ /ay/ # => 1
"Haystack" =~ /z/  # => nil

"Haystack" =~ 45 # => nil

def =~(regex : Regex) #

Tests whether str matches regex. If successful, it returns the position of the first match. If unsuccessful, it returns nil.

If the argument isn't a Regex, it returns nil.

"Haystack" =~ /ay/ # => 1
"Haystack" =~ /z/  # => nil

"Haystack" =~ 45 # => nil

def [](start : Int, count : Int) #

Returns a substring starting from the start character of size count.

The start argument can be negative to start counting from the end of the string.

Raises IndexError if start isn't in range.

Raises ArgumentError if count is negative.


def [](regex : Regex, group) #

def [](index : Int) #

Returns the Char at the given index, or raises IndexError if out of bounds.

Negative indices can be used to start counting from the end of the string.

"hello"[0]  # 'h'
"hello"[1]  # 'e'
"hello"[-1] # 'o'
"hello"[-2] # 'l'
"hello"[5]  # raises IndexError

def [](range : Range(Int, Int)) #

Returns a substring by using a Range's begin and end as character indices. Indices can be negative to start counting from the end of the string.

Raises IndexError if the range's start is not in range.

"hello"[0..2]   # "hel"
"hello"[0...2]  # "he"
"hello"[1..-1]  # "ello"
"hello"[1...-1] # "ell"

def [](str : String | Char) #

def [](regex : Regex) #

def []?(regex : Regex) #

def []?(index : Int) #

def []?(regex : Regex, group) #

def []?(str : String | Char) #

def ascii_only? #

Returns true if this String is comprised in its entirety by ASCII characters.

"hello".ascii_only? # => true
"你好".ascii_only?    # => false

def at(index : Int) #

def at(index : Int, &block) #

def blank? #

Returns true if this string consists exclusively of unicode whitespace.

"".blank?        # => true
"   ".blank?     # => true
"   a   ".blank? # => false

def byte_at(index, &block) #

def byte_at(index) #

def byte_at?(index) #

def byte_index(string : String, offset = 0) #

def byte_index(byte : Int, offset = 0) #

def byte_index_to_char_index(index) #

Returns the char index of a byte index, or nil if out of bounds.

It is valid to pass #bytesize to index, and in this case the answer will be the size of this string.


def byte_slice(start : Int, count : Int) #

def byte_slice(start : Int) #

def bytes #

Returns this string's bytes as an Array(UInt8).

"hello".bytes # => [104, 101, 108, 108, 111]
"你好".bytes    # => [228, 189, 160, 229, 165, 189]

def bytesize : Int32 #

Returns the number of bytes in this string.

"hello".bytesize # => 5
"你好".bytesize    # => 6

def camelcase #

Converts underscores to camelcase boundaries.

"eiffel_tower".camelcase # => "EiffelTower"

def capitalize(options = Unicode::CaseOptions::None) #

Returns a new String with the first letter converted to uppercase and every subsequent letter converted to lowercase.

"hEllO".capitalize # => "Hello"

def char_at(index) #

def char_index_to_byte_index(index) #

Returns the byte index of a char index, or nil if out of bounds.

It is valid to pass #size to index, and in this case the answer will be the bytesize of this string.

"hello".char_index_to_byte_index(1) # => 1
"hello".char_index_to_byte_index(5) # => 5
"こんにちは".char_index_to_byte_index(1) # => 3
"こんにちは".char_index_to_byte_index(5) # => 15

def chars #

Returns an Array of all characters in the string.

"ab☃".chars # => ['a', 'b', '☃']

def check_no_null_byte #

Raises an ArgumentError if self has null bytes. Returns self otherwise.

This method should sometimes be called before passing a String to a C function.


def chomp #

Returns a new String with the last carriage return removed (that is, it will remove \n, \r, and \r\n).

"string\r\n".chomp # => "string"
"string\n\r".chomp # => "string\n"
"string\n".chomp   # => "string"
"string".chomp     # => "string"
"x".chomp.chomp    # => "x"

def chomp(suffix : String) #

Returns a new String with suffix removed from the end of the string. If suffix is "\n" then "\r\n" is also removed if the string ends with it,

"hello".chomp("llo") # => "he"
"hello".chomp("ol")  # => "hello"

def chomp(suffix : Char) #

Returns a new String with suffix removed from the end of the string. If suffix is '\n' then "\r\n" is also removed if the string ends with it,

"hello".chomp('o') # => "hell"
"hello".chomp('a') # => "hello"

def clone #

def codepoint_at(index) #

def codepoints #

Returns an Array of the codepoints that make the string.

"ab☃".codepoints # => [97, 98, 9731]

See also: Char#ord.


def compare(other : String, case_insensitive = false) #

Compares this string with other, returning -1, 0 or +1 depending on whether this string is less, equal or greater than other, optionally in a case_insensitive manner.

If case_insitive is false, this method delegates to #<=>. Otherwise, the strings are compared char-by-char, and ASCII characters are compared in a case-insensitive way.

"abcdef".compare("abcde")   # => 1
"abcdef".compare("abcdef")  # => 0
"abcdef".compare("abcdefg") # => -1
"abcdef".compare("ABCDEF")  # => 1

"abcdef".compare("ABCDEF", case_insensitive: true) # => 0
"abcdef".compare("ABCDEG", case_insensitive: true) # => -1

def count(&block) #

Yields each char in this string to the block, returns the number of times the block returned a truthy value.

"aabbcc".count { |c| ['a', 'b'].includes?(c) } # => 4

def count(other : Char) #

Counts the occurrences of other char in this string.

"aabbcc".count('a') # => 2

def count(*sets) #

Sets should be a list of strings following the rules described at Char#in_set?. Returns the number of characters in this string that match the given set.


def delete(&block) #

Yields each char in this string to the block. Returns a new String with all characters for which the block returned a truthy value removed.

"aabbcc".delete { |c| ['a', 'b'].includes?(c) } # => "cc"

def delete(char : Char) #

Returns a new String with all occurrences of char removed.

"aabbcc".delete('b') # => "aacc"

def delete(*sets) #

Sets should be a list of strings following the rules described at Char#in_set?. Returns a new String with all characters that match the given set removed.

"aabbccdd".delete("a-c") # => "dd"

def downcase(options = Unicode::CaseOptions::None) #

Returns a new String with each uppercase letter replaced with its lowercase counterpart.

"hEllO".downcase # => "hello"

def dump(io) #

def dump #

def dump_unquoted(io) #

def dump_unquoted #

def dup #

def each_byte #

Returns an Iterator over each byte in the string.

bytes = "ab☃".each_byte
bytes.next # => 97
bytes.next # => 98
bytes.next # => 226
bytes.next # => 152
bytes.next # => 131

def each_byte(&block) #

Yields each byte in the string to the block.

array = [] of UInt8
"ab☃".each_byte do |byte|
  array << byte
end
array # => [97, 98, 226, 152, 131]

def each_char #

Returns an Iterator over each character in the string.

chars = "ab☃".each_char
chars.next # => 'a'
chars.next # => 'b'
chars.next # => '☃'

def each_char(&block) : Nil #

Yields each character in the string to the block.

array = [] of Char
"ab☃".each_char do |char|
  array << char
end
array # => ['a', 'b', '☃']

def each_char_with_index(&block) #

Yields each character and its index in the string to the block.

array = [] of Tuple(Char, Int32)
"ab☃".each_char_with_index do |char, index|
  array << {char, index}
end
array # => [{'a', 0}, {'b', 1}, {'☃', 2}]

def each_codepoint(&block) #

Yields each codepoint to the block.

array = [] of Int32
"ab☃".each_codepoint do |codepoint|
  array << codepoint
end
array # => [97, 98, 9731]

See also: Char#ord.


def each_codepoint #

Returns an Iterator for each codepoint.

codepoints = "ab☃".each_codepoint
codepoints.next # => 97
codepoints.next # => 98
codepoints.next # => 9731

See also: Char#ord.


def each_line(chomp = true) #

Returns an Iterator which yields each line of this string (see String#each_line).


def each_line(chomp = true, &block) : Nil #

Splits the string after each newline and yields each line to a block.

haiku = "the first cold shower
even the monkey seems to want
a little coat of straw"
haiku.each_line do |stanza|
  puts stanza.upcase
end
# => THE FIRST COLD SHOWER
# => EVEN THE MONKEY SEEMS TO WANT
# => A LITTLE COAT OF STRAW

def empty? #

Returns true if this is the empty string, "".


def encode(encoding : String, invalid : Symbol? = nil) : Bytes #

Returns a slice of bytes containing this string encoded in the given encoding.

The invalid argument can be:

  • nil: an exception is raised on invalid byte sequences
  • :skip: invalid byte sequences are ignored
"好".encode("GB2312") # => Bytes[186, 195]
"好".bytes            # => [229, 165, 189]

def ends_with?(char : Char) #

def ends_with?(str : String) #

def gsub(string : String, &block) #

Returns a String where all occurrences of the given string are replaced with the block's value.

"hello yellow".gsub("ll") { "dd" } # => "heddo yeddow"

def gsub(&block : Char -> _) #

Returns a String where each character yielded to the given block is replaced by the block's return value.

"hello".gsub { |char| char + 1 } # => "ifmmp"
"hello".gsub { "hi" }            # => "hihihihihi"

def gsub(char : Char, replacement) #

Returns a String where all occurrences of the given char are replaced with the given replacement.

"hello".gsub('l', "lo")      # => "heloloo"
"hello world".gsub('o', 'a') # => "hella warld"

def gsub(pattern : Regex, hash : Hash(String, _) | NamedTuple) #

Returns a String where all occurrences of the given pattern are replaced with a hash of replacements. If the hash contains the matched pattern, the corresponding value is used as a replacement. Otherwise the match is not included in the returned string.

# "he" and "l" are matched and replaced,
# but "o" is not and so is not included
"hello".gsub(/(he|l|o)/, {"he": "ha", "l": "la"}) # => "halala"

def gsub(pattern : Regex, replacement, backreferences = true) #

Returns a String where all occurrences of the given pattern are replaced with the given replacement.

"hello".gsub(/[aeiou]/, '*') # => "h*ll*"

Within replacement, the special match variable $~ will not refer to the current match.

If backreferences is true (the default value), replacement can include backreferences:

"hello".gsub(/[aeiou]/, "(\\0)") # => "h(e)ll(o)"

When substitution is performed, any backreferences found in replacement will be replaced with the contents of the corresponding capture group in pattern. Backreferences to capture groups that were not present in pattern or that did not match will be skipped. See Regex for information about capture groups.

Backreferences are expressed in the form "\\d", where d is a group number, or "\\k" where name is the name of a named capture group. A sequence of literal characters resembling a backreference can be expressed by placing "\\" before the sequence.

"foo".gsub(/o/, "x\\0x")                  # => "fxoxxox"
"foofoo".gsub(/(?<bar>oo)/, "|\\k<bar>|") # => "f|oo|f|oo|"
"foo".gsub(/o/, "\\\\0")                  # => "f\\0\\0"

Raises ArgumentError if an incomplete named back-reference is present in replacement.

Raises IndexError if a named group referenced in replacement is not present in pattern.


def gsub(string : String, replacement) #

Returns a String where all occurrences of the given string are replaced with the given replacement.

"hello yellow".gsub("ll", "dd") # => "heddo yeddow"

def gsub(hash : Hash(Char, _)) #

Returns a String where all chars in the given hash are replaced by the corresponding hash values.

"hello".gsub({'e' => 'a', 'l' => 'd'}) # => "haddo"

def gsub(tuple : NamedTuple) #

Returns a String where all chars in the given named tuple are replaced by the corresponding tuple values.

"hello".gsub({e: 'a', l: 'd'}) # => "haddo"

def gsub(pattern : Regex, &block) #

Returns a String where all occurrences of the given pattern are replaced by the block value's value.

"hello".gsub(/./) { |s| s[0].ord.to_s + ' ' } # => "104 101 108 108 111 "

def has_back_references? #

This returns true if this string has '\\' in it. It might not be a back reference, but '\\' is probably used for back references, so this check is faster than parsing the whole thing.


def hash #

Returns a hash based on this string’s size and content.

See also: Object#hash.


def hexbytes : Bytes #

Interprets this string as containing a sequence of hexadecimal values and decodes it as a slice of bytes. Two consecutive bytes in the string represent a byte in the returned slice.

Raises ArgumentError if this string does not denote an hexstring.

"0102031aff".hexbytes  # => Bytes[1, 2, 3, 26, 255]
"1".hexbytes           # raises ArgumentError
"hello world".hexbytes # raises ArgumentError

def hexbytes? : Bytes? #

Interprets this string as containing a sequence of hexadecimal values and decodes it as a slice of bytes. Two consecutive bytes in the string represent a byte in the returned slice.

Returns nil if this string does not denote an hexstring.

"0102031aff".hexbytes?  # => Bytes[1, 2, 3, 26, 255]
"1".hexbytes?           # => nil
"hello world".hexbytes? # => nil

def includes?(search : Char | String) #

Returns true if the string contains search.

"Team".includes?('i')            # => false
"Dysfunctional".includes?("fun") # => true

def index(search : Regex, offset = 0) #

Returns the index of search in the string, or nil if the string is not present. If offset is present, it defines the position to start the search.

"Hello, World".index('o')    # => 4
"Hello, World".index('Z')    # => nil
"Hello, World".index("o", 5) # => 8
"Hello, World".index("H", 2) # => nil
"Hello, World".index(/[ ]+/) # => 6
"Hello, World".index(/\d+/)  # => nil

def index(search : String, offset = 0) #

Returns the index of search in the string, or nil if the string is not present. If offset is present, it defines the position to start the search.

"Hello, World".index('o')    # => 4
"Hello, World".index('Z')    # => nil
"Hello, World".index("o", 5) # => 8
"Hello, World".index("H", 2) # => nil
"Hello, World".index(/[ ]+/) # => 6
"Hello, World".index(/\d+/)  # => nil

def index(search : Char, offset = 0) #

Returns the index of search in the string, or nil if the string is not present. If offset is present, it defines the position to start the search.

"Hello, World".index('o')    # => 4
"Hello, World".index('Z')    # => nil
"Hello, World".index("o", 5) # => 8
"Hello, World".index("H", 2) # => nil
"Hello, World".index(/[ ]+/) # => 6
"Hello, World".index(/\d+/)  # => nil

def insert(index : Int, other : Char) #

Returns a new String that results of inserting other in self at index. Negative indices count from the end of the string, and insert after the given index.

Raises IndexError if the index is out of bounds.

"abcd".insert(0, 'X')  # => "Xabcd"
"abcd".insert(3, 'X')  # => "abcXd"
"abcd".insert(4, 'X')  # => "abcdX"
"abcd".insert(-3, 'X') # => "abXcd"
"abcd".insert(-1, 'X') # => "abcdX"

"abcd".insert(5, 'X')  # raises IndexError
"abcd".insert(-6, 'X') # raises IndexError

def insert(index : Int, other : String) #

Returns a new String that results of inserting other in self at index. Negative indices count from the end of the string, and insert after the given index.

Raises IndexError if the index is out of bounds.

"abcd".insert(0, "FOO")  # => "FOOabcd"
"abcd".insert(3, "FOO")  # => "abcFOOd"
"abcd".insert(4, "FOO")  # => "abcdFOO"
"abcd".insert(-3, "FOO") # => "abFOOcd"
"abcd".insert(-1, "FOO") # => "abcdFOO"

"abcd".insert(5, "FOO")  # raises IndexError
"abcd".insert(-6, "FOO") # raises IndexError

def inspect(io) #

def inspect_unquoted #

def inspect_unquoted(io) #

def lchop #

Returns a new String with the first char removed from it. Applying lchop to an empty string returns an empty string.

"hello".lchop # => "ello"
"".lchop      # => ""

def lchop(prefix : String) #

Returns a new String with prefix removed from the beginning of the string.

"hello".lchop("hel") # => "lo"
"hello".lchop("eh")  # => "hello"

def lchop(prefix : Char) #

Returns a new String with prefix removed from the beginning of the string.

"hello".lchop('h') # => "ello"
"hello".lchop('g') # => "hello"

def lines(chomp = true) #

def ljust(len, char : Char = ' ') #

Adds instances of char to right of the string until it is at least size of len.

"Purple".ljust(8)      # => "Purple  "
"Purple".ljust(8, '-') # => "Purple--"
"Aubergine".ljust(8)   # => "Aubergine"

def lstrip(char : Char) #

Returns a new string with leading occurrences of char removed.

"aaabcdaaa".lstrip('a') # => "bcdaaa"

def lstrip #

Returns a new String with leading whitespace removed.

"    hello    ".lstrip # => "hello    "
"\tgoodbye\r\n".lstrip # => "goodbye\r\n"

def lstrip(&block : Char -> _) #

Returns a new string where leading characters for which the block returns a truthy value are removed.

"bcadefcba".lstrip { |c| 'a' <= c <= 'c' } # => "defcba"

def lstrip(chars : String) #

Returns a new string where leading occurrences of any char in chars are removed. The chars argument is not a suffix; rather; all combinations of its values are stripped.

"bcadefcba".lstrip("abc") # => "defcba"

def match(regex : Regex, pos = 0) : Regex::MatchData? #

Finds match of regex, starting at pos.


def partition(search : Regex) : Tuple(String, String, String) #

Searches separator or pattern (Regex) in the string, and returns a Tuple with the part before it, the match, and the part after it. If it is not found, returns str followed by two empty strings.

"hello".partition("l") # => {"he", "l", "lo"}
"hello".partition("x") # => {"hello", "", ""}

def partition(search : Char | String) : Tuple(String, String, String) #

Searches separator or pattern (Regex) in the string, and returns a Tuple with the part before it, the match, and the part after it. If it is not found, returns str followed by two empty strings.

"hello".partition("l") # => {"he", "l", "lo"}
"hello".partition("x") # => {"hello", "", ""}

def pretty_print(pp) #

def rchop #

Returns a new String with the last character removed. Applying rchop to an empty string returns an empty string.

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

def rchop(suffix : String) #

Returns a new String with suffix removed from the end of the string.

"string".rchop("ing") # => "str"
"string".rchop("inx") # => "string"

def rchop(suffix : Char) #

Returns a new String with suffix removed from the end of the string.

"string".rchop('g') # => "strin"
"string".rchop('x') # => "string"

def reverse #

Reverses the order of characters in the string.

"Argentina".reverse # => "anitnegrA"
"racecar".reverse   # => "racecar"

def rindex(search : Char, offset = size - 1) #

Returns the index of the last appearance of search in the string, If offset is present, it defines the position to end the search (characters beyond this point are ignored).

"Hello, World".rindex('o')    # => 8
"Hello, World".rindex('Z')    # => nil
"Hello, World".rindex("o", 5) # => 4
"Hello, World".rindex("W", 2) # => nil

def rindex(search : String, offset = size - search.size) #

Returns the index of the last appearance of search in the string, If offset is present, it defines the position to end the search (characters beyond this point are ignored).

"Hello, World".rindex('o')    # => 8
"Hello, World".rindex('Z')    # => nil
"Hello, World".rindex("o", 5) # => 4
"Hello, World".rindex("W", 2) # => nil

def rindex(search : Regex, offset = 0) #

Returns the index of the last appearance of search in the string, If offset is present, it defines the position to end the search (characters beyond this point are ignored).

"Hello, World".rindex('o')    # => 8
"Hello, World".rindex('Z')    # => nil
"Hello, World".rindex("o", 5) # => 4
"Hello, World".rindex("W", 2) # => nil

def rjust(len, char : Char = ' ') #

Adds instances of char to left of the string until it is at least size of len.

"Purple".rjust(8)      # => "  Purple"
"Purple".rjust(8, '-') # => "--Purple"
"Aubergine".rjust(8)   # => "Aubergine"

def rpartition(search : Char | String) : Tuple(String, String, String) #

Searches separator or pattern (Regex) in the string from the end of the string, and returns a Tuple with 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"}

def rpartition(search : Regex) : Tuple(String, String, String) #

Searches separator or pattern (Regex) in the string from the end of the string, and returns a Tuple with 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"}

def rstrip #

Returns a new String with trailing whitespace removed.

"    hello    ".rstrip # => "    hello"
"\tgoodbye\r\n".rstrip # => "\tgoodbye"

def rstrip(chars : String) #

Returns a new string where trailing occurrences of any char in chars are removed. The chars argument is not a suffix; rather; all combinations of its values are stripped.

"abcdefcba".rstrip("abc") # => "abcdef"

def rstrip(char : Char) #

Returns a new string with trailing occurrences of char removed.

"aaabcdaaa".rstrip('a') # => "aaabcd"

def rstrip(&block : Char -> _) #

Returns a new string where trailing characters for which the block returns a truthy value are removed.

"bcadefcba".rstrip { |c| 'a' <= c <= 'c' } # => "bcadef"

def scan(pattern : String) #

Searches the string for instances of pattern, returning an array of the matched string for each match.


def scan(pattern : Regex, &block) #

Searches the string for instances of pattern, yielding a Regex::MatchData for each match.


def scan(pattern : Regex) #

Searches the string for instances of pattern, returning an Array of Regex::MatchData for each match.


def scan(pattern : String, &block) #

Searches the string for instances of pattern, yielding the matched string for each match.


def scrub(replacement = Char::REPLACEMENT) : String #

Returns a String where bytes that are invalid in the UTF-8 encoding are replaced with replacement.


def size #

Returns the number of unicode codepoints in this string.

"hello".size # => 5
"你好".size    # => 2

def split(separator : Regex, limit = nil, &block : String -> _) #

Makes an Array by splitting the string on separator (and removing instances of separator).

If limit is present, the array will be limited to limit items and the final item will contain the remainder of the string.

If separator is an empty regex (//), the string will be separated into one-character strings.

long_river_name = "Mississippi"
long_river_name.split(/s+/) # => ["Mi", "i", "ippi"]
long_river_name.split(//)   # => ["M", "i", "s", "s", "i", "s", "s", "i", "p", "p", "i"]

def split(separator : Regex, limit = nil) #

Splits the string after each regex separator and yields each part to a block.

If limit is present, the array will be limited to limit items and the final item will contain the remainder of the string.

If separator is an empty regex (//), the string will be separated into one-character strings.

ary = [] of String
long_river_name = "Mississippi"

long_river_name.split(/s+/) { |s| ary << s }
ary # => ["Mi", "i", "ippi"]
ary.clear

long_river_name.split(//) { |s| ary << s }
ary # => ["M", "i", "s", "s", "i", "s", "s", "i", "p", "p", "i"]

def split(separator : String, limit = nil, &block : String -> _) #

Splits the string after each string separator and yields each part to a block.

If limit is present, the array will be limited to limit items and the final item will contain the remainder of the string.

If separator is an empty string (""), the string will be separated into one-character strings.

ary = [] of String
long_river_name = "Mississippi"

long_river_name.split("ss") { |s| ary << s }
ary # => ["Mi", "i", "ippi"]
ary.clear

long_river_name.split("i") { |s| ary << s }
ary # => ["M", "ss", "ss", "pp", ""]
ary.clear

long_river_name.split("") { |s| ary << s }
ary # => ["M", "i", "s", "s", "i", "s", "s", "i", "p", "p", "i"]

def split(limit : Int32? = nil) #

Makes an array by splitting the string on any ASCII whitespace characters (and removing that whitespace).

If limit is present, up to limit new strings will be created, with the entire remainder added to the last string.

old_pond = "
  Old pond
  a frog leaps in
  water's sound
"
old_pond.split    # => ["Old", "pond", "a", "frog", "leaps", "in", "water's", "sound"]
old_pond.split(3) # => ["Old", "pond", "a frog leaps in\n  water's sound\n"]

def split(limit : Int32? = nil, &block : String -> _) #

Splits the string after any ASCII whitespace character and yields each part to a block.

If limit is present, up to limit new strings will be created, with the entire remainder added to the last string.

ary = [] of String
old_pond = "
  Old pond
  a frog leaps in
  water's sound
"

old_pond.split { |s| ary << s }
ary # => ["Old", "pond", "a", "frog", "leaps", "in", "water's", "sound"]
ary.clear

old_pond.split(3) { |s| ary << s }
ary # => ["Old", "pond", "a frog leaps in\n  water's sound\n"]

def split(separator : Char, limit = nil) #

Makes an Array by splitting the string on the given character separator (and removing that character).

If limit is present, up to limit new strings will be created, with the entire remainder added to the last string.

"foo,bar,baz".split(',')    # => ["foo", "bar", "baz"]
"foo,bar,baz".split(',', 2) # => ["foo", "bar,baz"]

def split(separator : String, limit = nil) #

Makes an Array by splitting the string on separator (and removing instances of separator).

If limit is present, the array will be limited to limit items and the final item will contain the remainder of the string.

If separator is an empty string (""), the string will be separated into one-character strings.

long_river_name = "Mississippi"
long_river_name.split("ss") # => ["Mi", "i", "ippi"]
long_river_name.split("i")  # => ["M", "ss", "ss", "pp", ""]
long_river_name.split("")   # => ["M", "i", "s", "s", "i", "s", "s", "i", "p", "p", "i"]

def split(separator : Char, limit = nil, &block : String -> _) #

Splits the string after each character separator and yields each part to a block.

If limit is present, up to limit new strings will be created, with the entire remainder added to the last string.

ary = [] of String

"foo,bar,baz".split(',') { |string| ary << string }
ary # => ["foo", "bar", "baz"]
ary.clear

"foo,bar,baz".split(',', 2) { |string| ary << string }
ary # => ["foo", "bar,baz"]

def squeeze(&block) #

Yields each char in this string to the block. Returns a new String, that has all characters removed, that were the same as the previous one and for which the given block returned a truthy value.

"aaabbbccc".squeeze { |c| ['a', 'b'].includes?(c) } # => "abccc"
"aaabbbccc".squeeze { |c| ['a', 'c'].includes?(c) } # => "abbbc"

def squeeze(char : Char) #

Returns a new String, with all runs of char replaced by one instance.

"a    bbb".squeeze(' ') # => "a bbb"

def squeeze #

Returns a new String, that has all characters removed, that were the same as the previous one.

"a       bbb".squeeze # => "a b"

def squeeze(*sets : String) #

Sets should be a list of strings following the rules described at Char#in_set?. Returns a new String with all runs of the same character replaced by one instance, if they match the given set.

If no set is given, all characters are matched.

"aaabbbcccddd".squeeze("b-d") # => "aaabcd"
"a       bbb".squeeze         # => "a b"

def starts_with?(char : Char) #

def starts_with?(str : String) #

def strip(&block : Char -> _) #

Returns a new string where leading and trailing characters for which the block returns a truthy value are removed.

"bcadefcba".strip { |c| 'a' <= c <= 'c' } # => "def"

def strip #

Returns a new String with leading and trailing whitespace removed.

"    hello    ".strip # => "hello"
"\tgoodbye\r\n".strip # => "goodbye"

def strip(chars : String) #

Returns a new string where leading and trailing occurrences of any char in chars are removed. The chars argument is not a prefix or suffix; rather; all combinations of its values are stripped.

"abcdefcba".strip("abc") # => "def"

def strip(char : Char) #

Returns a new string where leading and trailing occurrences of char are removed.

"aaabcdaaa".strip('a') # => "bcd"

def sub(pattern : Regex, &block) #

Returns a String where the first occurrence of pattern is replaced by the block's return value.

"hello".sub(/./) { |s| s[0].ord.to_s + ' ' } # => "104 ello"

def sub(index : Int, replacement : Char) #

Returns a new String with the character at the given index replaced by replacement.

"hello".sub(1, 'a') # => "hallo"

def sub(index : Int, replacement : String) #

Returns a new String with the character at the given index replaced by replacement.

"hello".sub(1, "eee") # => "heeello"

def sub(range : Range(Int, Int), replacement : Char) #

Returns a new String with characters at the given range replaced by replacement.

"hello".sub(1..2, 'a') # => "halo"

def sub(range : Range(Int, Int), replacement : String) #

Returns a new String with characters at the given range replaced by replacement.

"hello".sub(1..2, "eee") # => "heeelo"

def sub(hash : Hash(Char, _)) #

Returns a String where the first char in the string matching a key in the given hash is replaced by the corresponding hash value.

"hello".sub({'a' => 'b', 'l' => 'd'}) # => "hedlo"

def sub(&block : Char -> _) #

Returns a new String where the first character is yielded to the given block and replaced by its return value.

"hello".sub { |char| char + 1 } # => "iello"
"hello".sub { "hi" }            # => "hiello"

def sub(char : Char, replacement) #

Returns a String where the first occurrence of char is replaced by replacement.

"hello".sub('l', "lo")      # => "helolo"
"hello world".sub('o', 'a') # => "hella world"

def sub(string : String, &block) #

Returns a String where the first occurrences of the given string is replaced with the block's value.

"hello yellow".sub("ll") { "dd" } # => "heddo yellow"

def sub(pattern : Regex, replacement, backreferences = true) #

Returns a String where the first occurrence of pattern is replaced by replacement

"hello".sub(/[aeiou]/, "*") # => "h*llo"

Within replacement, the special match variable $~ will not refer to the current match.

If backreferences is true (the default value), replacement can include backreferences:

"hello".sub(/[aeiou]/, "(\\0)") # => "h(e)llo"

When substitution is performed, any backreferences found in replacement will be replaced with the contents of the corresponding capture group in pattern. Backreferences to capture groups that were not present in pattern or that did not match will be skipped. See Regex for information about capture groups.

Backreferences are expressed in the form "\\d", where d is a group number, or "\\k<name>" where name is the name of a named capture group. A sequence of literal characters resembling a backreference can be expressed by placing "\\" before the sequence.

"foo".sub(/o/, "x\\0x")                  # => "fxoxo"
"foofoo".sub(/(?<bar>oo)/, "|\\k<bar>|") # => "f|oo|foo"
"foo".sub(/o/, "\\\\0")                  # => "f\\0o"

Raises ArgumentError if an incomplete named back-reference is present in replacement.

Raises IndexError if a named group referenced in replacement is not present in pattern.


def sub(pattern : Regex, hash : Hash(String, _) | NamedTuple) #

Returns a String where the first occurrences of the given pattern is replaced with the matching entry from the hash of replacements. If the first match is not included in the hash, nothing is replaced.

"hello".sub(/(he|l|o)/, {"he": "ha", "l": "la"}) # => "hallo"
"hello".sub(/(he|l|o)/, {"l": "la"})             # => "hello"

def sub(string : String, replacement) #

Returns a String where the first occurrences of the given string is replaced with the given replacement.

"hello yellow".sub("ll", "dd") # => "heddo yellow"

def succ #

Returns the successor of the string. The successor is calculated by incrementing characters starting from the rightmost alphanumeric (or the rightmost character if there are no alphanumerics) in the string. Incrementing a digit always results in another digit, and incrementing a letter results in another letter of the same case.

If the increment generates a "carry", the character to the left of it is incremented. This process repeats until there is no carry, adding an additional character if necessary.

"abcd".succ      # => "abce"
"THX1138".succ   # => "THX1139"
"((koala))".succ # => "((koalb))"
"1999zzz".succ   # => "2000aaa"
"ZZZ9999".succ   # => "AAAA0000"
"***".succ       # => "**+"

def to_big_f #

def to_big_i(base = 10) : BigInt #

Returns a BigInt from this string, in the given base.

Raises ArgumentError if this string doesn't denote a valid integer.


def to_f(whitespace = true, strict = true) #

Returns the result of interpreting characters in this string as a floating point number (Float64). This method raises an exception if the string is not a valid float representation.

Options:

  • whitespace: if true, leading and trailing whitespaces are allowed
  • strict: if true, extraneous characters past the end of the number are disallowed
"123.45e1".to_f                # => 1234.5
"45.67 degrees".to_f           # raises ArgumentError
"thx1138".to_f(strict: false)  # raises ArgumentError
" 1.2".to_f(whitespace: false) # raises ArgumentError
"1.2foo".to_f(strict: false)   # => 1.2

def to_f32(whitespace = true, strict = true) #

Same as #to_f but returns a Float32.


def to_f32?(whitespace = true, strict = true) #

Same as #to_f? but returns a Float32.


def to_f64(whitespace = true, strict = true) #

Same as #to_f.


def to_f64?(whitespace = true, strict = true) #

Same as #to_f?.


def to_f?(whitespace = true, strict = true) #

Returns the result of interpreting characters in this string as a floating point number (Float64). This method returns nil if the string is not a valid float representation.

Options:

  • whitespace: if true, leading and trailing whitespaces are allowed
  • strict: if true, extraneous characters past the end of the number are disallowed
"123.45e1".to_f?                # => 1234.5
"45.67 degrees".to_f?           # => nil
"thx1138".to_f?                 # => nil
" 1.2".to_f?(whitespace: false) # => nil
"1.2foo".to_f?(strict: false)   # => 1.2

def to_i(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true, &block) #

Same as #to_i, but returns the block's value if there is not a valid number at the start of this string, or if the resulting integer doesn't fit an Int32.

"12345".to_i { 0 } # => 12345
"hello".to_i { 0 } # => 0

def to_i(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) #

Returns the result of interpreting leading characters in this string as an integer base base (between 2 and 36).

If there is not a valid number at the start of this string, or if the resulting integer doesn't fit an Int32, an ArgumentError is raised.

Options:

  • whitespace: if true, leading and trailing whitespaces are allowed
  • underscore: if true, underscores in numbers are allowed
  • prefix: if true, the prefixes "0x", "0" and "0b" override the base
  • strict: if true, extraneous characters past the end of the number are disallowed
"12345".to_i             # => 12345
"0a".to_i                # raises ArgumentError
"hello".to_i             # raises ArgumentError
"0a".to_i(16)            # => 10
"1100101".to_i(2)        # => 101
"1100101".to_i(8)        # => 294977
"1100101".to_i(10)       # => 1100101
"1100101".to_i(base: 16) # => 17826049

"12_345".to_i                   # raises ArgumentError
"12_345".to_i(underscore: true) # => 12345

"  12345  ".to_i                    # => 12345
"  12345  ".to_i(whitespace: false) # raises ArgumentError

"0x123abc".to_i               # raises ArgumentError
"0x123abc".to_i(prefix: true) # => 1194684

"99 red balloons".to_i                # raises ArgumentError
"99 red balloons".to_i(strict: false) # => 99

def to_i16(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true, &block) #

Same as #to_i but returns an Int16 or the block's value.


def to_i16(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : Int16 #

Same as #to_i but returns an Int16.


def to_i16?(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : Int16? #

Same as #to_i but returns an Int16 or nil.


def to_i32(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : Int32 #

Same as #to_i.


def to_i32(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true, &block) #

Same as #to_i.


def to_i32?(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : Int32? #

Same as #to_i.


def to_i64(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true, &block) #

Same as #to_i but returns an Int64 or the block's value.


def to_i64(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : Int64 #

Same as #to_i but returns an Int64.


def to_i64?(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : Int64? #

Same as #to_i but returns an Int64 or nil.


def to_i8(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : Int8 #

Same as #to_i but returns an Int8.


def to_i8(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true, &block) #

Same as #to_i but returns an Int8 or the block's value.


def to_i8?(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : Int8? #

Same as #to_i but returns an Int8 or nil.


def to_i?(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) #

Same as #to_i, but returns nil if there is not a valid number at the start of this string, or if the resulting integer doesn't fit an Int32.

"12345".to_i?             # => 12345
"99 red balloons".to_i?   # => nil
"0a".to_i?(strict: false) # => 0
"hello".to_i?             # => nil

def to_json(json : JSON::Builder) #

def to_s(io) #

def to_s #

def to_slice : Bytes #

Returns the underlying bytes of this String in an unsafe way.

The returned slice is read-only.


def to_u16(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : UInt16 #

Same as #to_i but returns an UInt16.


def to_u16(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true, &block) #

Same as #to_i but returns an UInt16 or the block's value.


def to_u16?(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : UInt16? #

Same as #to_i but returns an UInt16 or nil.


def to_u32(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true, &block) #

Same as #to_i but returns an UInt32 or the block's value.


def to_u32(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : UInt32 #

Same as #to_i but returns an UInt32.


def to_u32?(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : UInt32? #

Same as #to_i but returns an UInt32 or nil.


def to_u64(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true, &block) #

Same as #to_i but returns an UInt64 or the block's value.


def to_u64(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : UInt64 #

Same as #to_i but returns an UInt64.


def to_u64?(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : UInt64? #

Same as #to_i but returns an UInt64 or nil.


def to_u8(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : UInt8 #

Same as #to_i but returns an UInt8.


def to_u8(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true, &block) #

Same as #to_i but returns an UInt8 or the block's value.


def to_u8?(base : Int = 10, whitespace = true, underscore = false, prefix = false, strict = true) : UInt8? #

Same as #to_i but returns an UInt8 or nil.


def to_unsafe : Pointer(UInt8) #

Returns a pointer to the underlying bytes of this String.


def to_yaml(yaml : YAML::Builder) #

def tr(from : String, to : String) #

Returns a new string translating characters using from and to as a map. If to is shorter than from, the last character in to is used for the rest. If to is empty, this acts like String#delete.

"aabbcc".tr("abc", "xyz") # => "xxyyzz"
"aabbcc".tr("abc", "x")   # => "xxxxxx"
"aabbcc".tr("a", "xyz")   # => "xxbbcc"

def underscore #

Converts camelcase boundaries to underscores.

"DoesWhatItSaysOnTheTin".underscore # => "does_what_it_says_on_the_tin"
"PartyInTheUSA".underscore          # => "party_in_the_usa"
"HTTP_CLIENT".underscore            # => "http_client"

def unsafe_byte_at(index) #

def unsafe_byte_slice(byte_offset, count) #

def unsafe_byte_slice(byte_offset) #

def upcase(options = Unicode::CaseOptions::None) #

Returns a new String with each lowercase letter replaced with its uppercase counterpart.

"hEllO".upcase # => "HELLO"

def valid_encoding? #

Returns true if this String is encoded correctly according to the UTF-8 encoding.