# Programming Ruby ### The Pragmatic Programmer's Guide
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class String |
Parent: | Object
Version: | 1.6

### Index:

new % * + << <=> == === =~ [ ] [ ]= ~ capitalize capitalize! center chomp chomp! chop chop! concat count crypt delete delete! downcase downcase! dump each each_byte each_line empty? gsub gsub! hash hex include? index intern length ljust next next! oct replace reverse reverse! rindex rjust scan size slice slice! split squeeze squeeze! strip strip! sub sub! succ succ! sum swapcase swapcase! to_f to_i to_s to_str tr tr! tr_s tr_s! unpack upcase upcase! upto

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 (see page 202).

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#[]=` .

mixins
Comparable: | <, <=, ==, >=, >, between?
Enumerable: | collect, detect, each_with_index, entries, find, find_all, grep, include?, map, max, member?, min, reject, select, sort, to_a

class methods
new | String.new( aString ) -> aNewString
|  | Returns a new string object containing a copy of aString.

instance methods
% | str % arg -> aString
|  | Format---Uses str as a format specification, and returns the result of applying it to arg. If the format specification contains more than one substitution, then arg must be an `Array` containing the values to be substituted. See `Kernel::sprintf` on page 423 for details of the format string.
`"%05d" % 123` | » | `"00123"`
`"%-5s: %08x" % [ "ID", self.id ]` | » | `"ID:200e1670"`
* | str * anInteger -> aString
|  | Copy---Returns a new `String` containing anInteger copies of the receiver.
`"Ho! " * 3` | » | `"Ho! Ho! Ho! "`
+ | str + aString -> aNewString
|  | Concatenation---Returns a new `String` containing aString concatenated to str.
`"Hello from " + self.to_s` | » | `"Hello from main"`
<< | str << aFixnum -> str str << anObject -> str
|  | Append---Concatenates the given object to str. If the object is a `Fixnum` between 0 and 255, it is converted to a character before concatenation.
`a = "hello "`
`a << "world"` | » | `"hello world"`
`a << 33` | » | `"hello world!"`
`a` | » | `"hello world!"`
<=> | str <=> aString -> -1, 0, +1
|  | Comparison---Returns -1 if str is less than, 0 if str is equal to, and +1 if str is greater than aString. 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. If the variable `$=` is `false`, the comparison is based on comparing the binary values of each character in the string. If `$=` is not `false`, then the comparison is case insensitive.[The locale is ignored when case-insensitive comparisons are performed, so ``\"o'' will not match ``\"O''.] `<=>` is the basis for the methods `<`, `<=`, `>`, `>=`, and `between?`, included from module `Comparable`. The method `String#==` does not use `Comparable#==` .
`"abcdef" <=> "abcde"` | » | `1`
`"abcdef" <=> "abcdef"` | » | `0`
`"abcdef" <=> "abcdefg"` | » | `-1`
`"abcdef" <=> "ABCDEF"` | » | `1`
`$= = true`
`"abcdef" <=> "ABCDEF"` | » | `0`
== | str == anObject -> `true` or `false`
|  | Equality---If anObject is not a `String`, returns `false`. Otherwise, returns `true` if str `<=>` anObject returns zero.
=== | str === anObject -> `true` or `false`
|  | Case Equality---Synonym for `String#==` .
=~ | str =~ anObject -> aFixnum or `nil`
|  | Match---If anObject is a `Regexp` or a `String`, uses it as a pattern to match against str. Returns the position the match starts, or `nil` if there is no match. Otherwise, invokes anObject.=~, passing str as an argument. The default `=~` in `Object` returns `false`.
`"cat o' 9 tails" =~ "\\d"` | » | `7`
`"cat o' 9 tails" =~ /\d/` | » | `7`
`"cat o' 9 tails" =~ 9` | » | `false`
[ ] | str[ aFixnum ] -> aFixnum or `nil` str[ aFixnum, aFixnum ] -> aString or `nil` str[ aRange ] -> aString or `nil` str[ aRegexp ] -> aString or `nil` str[ aString ] -> aString or `nil`
|  | Element Reference---If passed a single `Fixnum`, returns the code of the character at that position. If passed two `Fixnum` 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 characters 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. If a `Regexp` is supplied, the matching portion of str is returned. If a `String` is given, that string is returned if it occurs in str. In both cases, `nil` is returned if there is no match.
`a = "hello there"`
`a[1]` | » | `101`
`a[1,3]` | » | `"ell"`
`a[1..3]` | » | `"ell"`
`a[-3,2]` | » | `"er"`
`a[-4..-2]` | » | `"her"`
`a[-2..-4]` | » | `nil`
`a[/th[aeiou]/]` | » | `"the"`
`a["lo"]` | » | `"lo"`
`a["bye"]` | » | `nil`
[ ]= | str[ aFixnum ] = aFixnum str[ aFixnum ] = aString str[ aFixnum, aFixnum ] = aString str[ aRange ] = aString str[ aRegexp ] = aString str[ aString ] = aString
|  | 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. The forms that take a `Fixnum` will raise an `IndexError` if the value is out of range; the `Range` form will raise a `RangeError`, and the `Regexp` and `String` forms will silently ignore the assignment.
`a = "hello"; a[2] = 96; a` | » | `"he`lo"`
`a = "hello"; a[2, 4] = "xyz"; a` | » | `"hexyz"`
`a = "hello"; a[-4, 2] = "xyz"; a` | » | `"hxyzlo"`
`a = "hello"; a[2..4] = "xyz"; a` | » | `"hexyz"`
`a = "hello"; a[-4..-2] = "xyz"; a` | » | `"hxyzo"`
`a = "hello"; a[/[el]+/] = "xyz"; a` | » | `"hxyzo"`
`a = "hello"; a["l"] = "xyz"; a` | » | `"hexyzlo"`
`a = "hello"; a["ll"] = "xyz"; a` | » | `"hexyzo"`
`a = "hello"; a["bad"] = "xyz"; a` | » | `"hello"`
`a = "hello"; a[2, 0] = "xyz"; a` | » | `"hexyzllo"`
~ | ~str -> aFixnum or `nil`
|  | Equivalent to `$_` `=~ str` .
capitalize | str.capitalize -> aString
|  | Returns a copy of str with the first character converted to uppercase and the remainder to lowercase.
`"hello".capitalize` | » | `"Hello"`
`"HELLO".capitalize` | » | `"Hello"`
`"123ABC".capitalize` | » | `"123abc"`
capitalize! | str.capitalize! -> str or `nil`
|  | Modifies str by converting the first character to uppercase and the remainder to lowercase. Returns `nil` if no changes are made.
`a = "hello"`
`a.capitalize!` | » | `"Hello"`
`a` | » | `"Hello"`
`a.capitalize!` | » | `nil`
center | str.center( anInteger ) -> aString
|  | If anInteger is greater than the length of str, returns a new `String` of length anInteger with str centered between spaces; otherwise, returns str.
`"hello".center(4)` | » | `"hello"`
`"hello".center(20)` | » | `"hello"`
chomp | str.chomp( aString=`$/` ) -> aString
|  | Returns a new `String` with the given record separator removed from the end of str (if present).
`"hello".chomp` | » | `"hello"`
`"hello\n".chomp` | » | `"hello"`
`"hello \n there".chomp` | » | `"hello \n there"`
`"hello".chomp("llo")` | » | `"he"`
chomp! | str.chomp!( aString=`$/` ) -> str or `nil`
|  | Modifies str in place as described for `String#chomp` , returning str, or `nil` if no modifications were made.
chop | str.chop -> aString
|  | 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` | » | `""`
chop! | str.chop! -> str or `nil`
|  | Processes str as for `String#chop` , returning str, or `nil` if str is the empty string. See also `String#chomp!` .
concat | str.concat( aFixnum ) -> str str.concat( anObject ) -> str
|  | Synonym for `String#<<` .
count | str.count( [ aString ]+ ) -> aFixnum
|  | Each aString parameter defines a set of characters to count. The intersection of these sets defines the characters to count in str. Any aString that starts with a caret (^) is negated. The sequence c1--c2 means all characters between c1 and c2.
`a = "hello world"`
`a.count "lo"` | » | `5`
`a.count "lo", "o"` | » | `2`
`a.count "hello", "^l"` | » | `4`
`a.count "ej-m"` | » | `4`
crypt | str.crypt( aString ) -> aString
|  | Applies a one-way cryptographic hash to str by invoking the standard library function `crypt`. The argument is the salt string, which should be two characters long, each character drawn from `[a-zA-Z0-9./]`.
delete | str.delete( [ aString ]+ ) -> aString
|  | 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"`
delete! | str.delete!( [ aString ]+ ) -> str or `nil`
|  | Performs a `delete` operation in place, returning str, or `nil` if str was not modified.
downcase | str.downcase -> aString
|  | Returns a copy of str with all uppercase letters replaced with their lowercase counterparts. The operation is locale insensitive---only characters ``A'' to ``Z'' are affected.
`"hEllO".downcase` | » | `"hello"`
downcase! | str.downcase! -> str or `nil`
|  | Downcases the contents of str, returning `nil` if no changes were made.
dump | str.dump -> aString
|  | Produces a version of str with all nonprinting characters replaced by `\nnn` notation and all special characters escaped.
each | str.each( aString=`$/` ) {| substr | block } -> str
|  | Splits str using the supplied parameter as the record separator (`$/` by default), passing each substring in turn to the supplied block. If a zero-length record separator is supplied, the string is split on `\n` characters, except that multiple successive newlines are appended together.
    print "Example one\n"
    "hello\nworld".each {|s| p s}
    print "Example two\n"
    "hello\nworld".each('l') {|s| p s}
    print "Example three\n"
    "hello\n\n\nworld".each('') {|s| p s}
produces:
    Example one
    "hello\n"
    "world"
    Example two
    "hel"
    "l"
    "o\nworl"
    "d"
    Example three
    "hello\n\n\n"
    "world"
each_byte | str.each_byte {| aFixnum | block } -> str
|  | Passes each byte in str to the given block.
    "hello".each_byte {|c| print c, ' ' }
produces:
    104 101 108 108 111
each_line | str.each_line( aString=`$/` ) {| substr | block } -> str
|  | Synonym for `String#each` .
empty? | str.empty? -> `true` or `false`
|  | Returns `true` if str has a length of zero.
`"hello".empty?` | » | `false`
`"".empty?` | » | `true`
gsub | str.gsub( pattern, replacement ) -> aString str.gsub( pattern ) {| match | block } -> aString
|  | Returns a copy of str with all occurrences of pattern replaced with either replacement or the value of the block. If a string is used as the replacement, special variables from the match (such as `$&` and `$1`) cannot be substituted into it, as substitution into the string occurs before the pattern match starts. However, the sequences `\1`, `\2`, and so on may be used to interpolate successive groups in the match. These sequences are shown in Table 22.7 on page 371.
Backslash sequences in substitution strings
Sequence | Text That Is Substituted
`\1, \2, ... \9` | The value matched by the nth grouped subexpression
`\&` | The last match
`\`` | The part of the string before the match
`\'` | The part of the string after the match
`\+` | The highest-numbered group matched
In the block form, the current match is passed in as a parameter, and variables such as `$1`, `$2`, `$``, `$&`, and `$'` will be set appropriately. The value returned by the block will be substituted for the match on each call. The result inherits any tainting in the original string or any supplied replacement string.
`"hello".gsub(/[aeiou]/, '*')` | » | `"h*ll*"`
`"hello".gsub(/([aeiou])/, '<\1>')` | » | `"h<e>ll<o>"`
`"hello".gsub('.') {|s| s[0].to_s + ' '}` | » | `"104 101 108 108 111 "`
gsub! | str.gsub!( pattern, replacement ) -> str or `nil` str.gsub!( pattern ) {| match | block } -> str or `nil`
|  | Performs the substitutions of `String#gsub` in place, returning str, or `nil` if no substitutions were performed.
hash | str.hash -> aFixnum
|  | Generates a `Fixnum` hash value for str. If `$=` is `true`, the hash will be case insensitive.
`$= = true`
`hash = { 'cat' => 'Feline', 'dog' => 'canine' }`
`hash['cat']` | » | `"Feline"`
`hash['cAt']` | » | `"Feline"`
`$= = false`
`hash.rehash # re-calculate hash values` | » | `{"cat"=>"Feline", "dog"=>"canine"}`
`hash['cat']` | » | `"Feline"`
`hash['cAt']` | » | `nil`
hex | str.hex -> anInteger
|  | 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`
include? | str.include? aString -> `true` or `false` str.include? aFixnum -> `true` or `false`
|  | Returns `true` if str contains the given string or character.
`"hello".include? "lo"` | » | `true`
`"hello".include? "ol"` | » | `false`
`"hello".include? ?h` | » | `true`
index | str.index( aString [, anOffset ] ) -> aFixnum or `nil` str.index( aFixnum [, anOffset ] ) -> aFixnum or `nil` str.index( aRegexp [, anOffset ] ) -> aFixnum or `nil`
|  | Returns the index of the first occurrence of the given substring, character, or pattern in str. Returns `nil` if not found. If the second parameter is present, it specifies the position in the string to begin the search.
`"hello".index('e')` | » | `1`
`"hello".index('lo')` | » | `3`
`"hello".index('a')` | » | `nil`
`"hello".index(101)` | » | `1`
`"hello".index(/[aeiou]/, -3)` | » | `4`
intern | str.intern -> aSymbol
|  | Returns the `Symbol` corresponding to str, creating the symbol if it did not previously exist. See `Symbol#id2name` on page 384.
`"Koala".intern` | » | `:Koala`
length | str.length -> anInteger
|  | Returns the length of str.
ljust | str.ljust( anInteger ) -> aString
|  | If anInteger is greater than the length of str, returns a new `String` of length anInteger with str left justified and space padded; otherwise, returns str.
`"hello".ljust(4)` | » | `"hello"`
`"hello".ljust(20)` | » | `"hello"`
next | str.next -> aString
|  | Synonym for `String#succ` .
next! | str.next! -> str
|  | Synonym for `String#succ!` .
oct | str.oct -> anInteger
|  | 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`
replace | str.replace( aString ) -> str
|  | Replaces the contents and taintedness of str with the corresponding values in aString.
`s = "hello"` | » | `"hello"`
`s.replace "world"` | » | `"world"`
reverse | str.reverse -> aString
|  | Returns a new string with the characters from str in reverse order.
`"stressed".reverse` | » | `"desserts"`
reverse! | str.reverse! -> str
|  | Reverses str in place.
rindex | str.rindex( aString [, aFixnum ] ) -> aFixnum or `nil` str.rindex( aFixnum [, aFixnum ] ) -> aFixnum or `nil` str.rindex( aRegexp [, aFixnum ] ) -> aFixnum or `nil`
|  | Returns the index of the last occurrence of the given substring, character, or pattern in str. Returns `nil` if not found. If the second parameter is present, it specifies the position in the string to end the search---characters beyond this point will not be considered.
`"hello".rindex('e')` | » | `1`
`"hello".rindex('l')` | » | `3`
`"hello".rindex('a')` | » | `nil`
`"hello".rindex(101)` | » | `1`
`"hello".rindex(/[aeiou]/, -2)` | » | `1`
rjust | str.rjust( anInteger ) -> aString
|  | If anInteger is greater than the length of str, returns a new `String` of length anInteger with str right justified and space padded; otherwise, returns str.
`"hello".rjust(4)` | » | `"hello"`
`"hello".rjust(20)` | » | `"hello"`
scan | str.scan( pattern ) -> anArray str.scan( pattern ) {| match, ...| block } -> str
|  | 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(/(.)(.)/) {|a,b| print b, a }
    print "\n"
produces:
    <<cruel>> <<world>>
    rceu lowlr
size | str.size -> anInteger
|  | Synonym for `String#length` .
slice | str.slice( aFixnum ) -> aFixnum or `nil` str.slice( aFixnum, aFixnum ) -> aString or `nil` str.slice( aRange ) -> aString or `nil` str.slice( aRegexp ) -> aString or `nil` str.slice( aString ) -> aString or `nil`
|  | Synonym for `String#[ ]` .
`a = "hello there"`
`a.slice(1)` | » | `101`
`a.slice(1,3)` | » | `"ell"`
`a.slice(1..3)` | » | `"ell"`
`a.slice(-3,2)` | » | `"er"`
`a.slice(-4..-2)` | » | `"her"`
`a.slice(-2..-4)` | » | `nil`
`a.slice(/th[aeiou]/)` | » | `"the"`
`a.slice("lo")` | » | `"lo"`
`a.slice("bye")` | » | `nil`
slice! | str.slice!( aFixnum ) -> aFixnum or `nil` str.slice!( aFixnum, aFixnum ) -> aString or `nil` str.slice!( aRange ) -> aString or `nil` str.slice!( aRegexp ) -> aString or `nil` str.slice!( aString ) -> aString or `nil`
|  | Deletes the specified portion from str, and returns the portion deleted. The forms that take a `Fixnum` will raise an `IndexError` if the value is out of range; the `Range` form will raise a `RangeError`, and the `Regexp` and `String` forms will silently ignore the assignment.
`string = "this is a string"`
`string.slice!(2)` | » | `105`
`string.slice!(3..6)` | » | `" is "`
`string.slice!(/s.*t/)` | » | `"sa st"`
`string.slice!("r")` | » | `"r"`
`string` | » | `"thing"`
split | str.split( pattern=`$;`, [ limit ] ) -> anArray
|  | Divides str into substrings based on a delimiter, returning an array of these substrings. If pattern is a `String`, then its contents are used as the delimiter when splitting str. If pattern is a single space, str is split on whitespace, with leading whitespace and runs of contiguous whitespace characters ignored. If pattern is a `Regexp`, str is divided where the pattern matches. Whenever the pattern matches a zero-length string, str is split into individual characters. If pattern is omitted, the value of `$;` 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 supressed. If limit is a positive number, at most that number of fields will be returned (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 supressed.
`" 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(/,\s*/)` | » | `["1", "2.34", "56", "7"]`
`"hello".split(//)` | » | `["h", "e", "l", "l", "o"]`
`"hello".split(//, 3)` | » | `["h", "e", "llo"]`
`"hi mom".split(/\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", "", ""]`
squeeze | str.squeeze( [ aString ]* ) -> aNewString
|  | Builds a set of characters from the aString parameter(s) using the procedure described for `String#count` on page 368. 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"`
squeeze! | str.squeeze!( [ aString ]* ) -> str or `nil`
|  | Squeezes str in place, returning either str, or `nil` if no changes were made.
strip | str.strip -> aString
|  | Returns a copy of str with leading and trailing whitespace removed.
`" hello ".strip` | » | `"hello"`
`"\tgoodbye\r\n".strip` | » | `"goodbye"`
strip! | str.strip! -> str or `nil`
|  | Removes leading and trailing whitespace from str. Returns `nil` if str was not altered.
sub | str.sub( pattern, replacement ) -> aString str.sub( pattern ) {| match | block } -> aString
|  | Returns a copy of str with the first occurrence of pattern replaced with either replacement or the value of the block. If the string form of the method is used, special variables such as `$&` will not be useful, as substitution into the string occurs before the pattern match starts. However, the sequences `\1`, `\2`, listed in Table 22.7 on page 371 may be used. In the block form, the current match is passed in as a parameter, and variables such as `$1`, `$2`, `$``, `$&`, and `$'` will be set appropriately. 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[0].to_s + ' ' }` | » | `"104 ello"`
sub! | str.sub!( pattern, replacement ) -> str or `nil` str.sub!( pattern ) {| match | block } -> str or `nil`
|  | Performs the substitutions of `String#sub` in place, returning str, or `nil` if no substitutions were performed.
succ | str.succ -> aString
|  | Returns the successor to str. 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. Incrementing nonalphanumerics uses the underlying character set's collating sequence. 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` | » | `"**+"`
succ! | str.succ! -> str
|  | Equivalent to `String#succ` , but modifies the receiver in place.
sum | str.sum( aFixnum=16 ) -> anInteger
|  | Returns a basic n-bit checksum of the characters in str, where n is the optional parameter, defaulting to 16. The result is simply the sum of the binary value of each character in str modulo 2n - 1. This is not a particularly good checksum.
swapcase | str.swapcase -> aString
|  | Returns a copy of str with uppercase alphabetic characters converted to lowercase and lowercase characters converted to uppercase.
`"Hello".swapcase` | » | `"hELLO"`
`"cYbEr_PuNk11".swapcase` | » | `"CyBeR_pUnK11"`
swapcase! | str.swapcase! -> str or `nil`
|  | Equivalent to `String#swapcase` , but modifies the receiver in place, returning str, or `nil` if no changes were made.
to_f | str.to_f -> aFloat
|  | 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. The method never raises an exception.
`"123.45e1".to_f` | » | `1234.5`
`"45.67 degrees".to_f` | » | `45.67`
`"thx1138".to_f` | » | `0.0`
to_i | str.to_i -> anInteger
|  | Returns the result of interpreting leading characters in str as a decimal integer. 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. The method never raises an exception.
`"12345".to_i` | » | `12345`
`"99 red balloons".to_i` | » | `99`
`"0x0a".to_i` | » | `0`
`"hello".to_i` | » | `0`
to_s | str.to_s -> str
|  | Returns the receiver.
to_str | str.to_str -> str
|  | Synonym for `String#to_s` . `to_str` is used by methods such as `String#concat` to convert their arguments to a string. Unlike `to_s`, which is supported by almost all classes, `to_str` is normally implemented only by those classes that act like strings. Of the built-in classes, only `Exception` and `String` implement `to_str`.
tr | str.tr( fromString, toString ) -> aString
|  | Returns a copy of str with the characters in fromString replaced by the corresponding characters in toString. If toString is shorter than fromString, it is padded with its last character. Both strings may use the c1--c2 notation to denote ranges of characters, and fromString may start with a `^`, which denotes all characters except those listed.
`"hello".tr('aeiou', '*')` | » | `"h*ll*"`
`"hello".tr('^aeiou', '*')` | » | `"*e**o"`
`"hello".tr('el', 'ip')` | » | `"hippo"`
`"hello".tr('a-y', 'b-z')` | » | `"ifmmp"`
tr! | str.tr!( fromString, toString ) -> str or `nil`
|  | Translates str in place, using the same rules as `String#tr` . Returns str, or `nil` if no changes were made.
tr_s | str.tr_s( fromString, toString ) -> aString
|  | 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"`
tr_s! | str.tr_s!( fromString, toString ) -> str or `nil`
|  | Performs `String#tr_s` processing on str in place, returning str, or `nil` if no changes were made.
unpack | str.unpack( format ) -> anArray
|  | 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 Table 22.8 on page 379. 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 (```_`'') 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 `Array#pack` on page 286.
Directives for `String#unpack`
Format | Function | Returns
A | String with trailing nulls and spaces removed. | String
a | String. | String
B | Extract bits from each character (msb first). | String
b | Extract bits from each character (lsb first). | String
C | Extract a character as an unsigned integer. | Fixnum
c | Extract a character as an integer. | Fixnum
d | Treat sizeof(double) characters as a native double. | Float
E | Treat sizeof(double) characters as a double in little-endian byte order. | Float
e | Treat sizeof(float) characters as a float in little-endian byte order. | Float
f | Treat sizeof(float) characters as a native float. | Float
G | Treat sizeof(double) characters as a double in network byte order. | Float
g | Treat sizeof(float) characters as a float in network byte order. | Float
H | Extract hex nibbles from each character (most significant first). | String
h | Extract hex nibbles from each character (least significant first). | String
I | Treat sizeof(int) 1 successive characters as an unsigned native integer. | Integer
i | Treat sizeof(int) 1 successive characters as a signed native integer. | Integer
L | Treat four1 successive characters as an unsigned native long integer. | Integer
l | Treat four1 successive characters as a signed native long integer. | Integer
M | Extract a quoted-printable string. | String
m | Extract a base64 encoded string. | String
N | Treat four characters as an unsigned long in network byte order. | Fixnum
n | Treat two characters as an unsigned short in network byte order. | Fixnum
P | Treat sizeof(char *) characters as a pointer, and return len characters from the referenced location. | String
p | Treat sizeof(char *) characters as a pointer to a null-terminated string. | String
S | Treat two1 successive characters as an unsigned short in native byte order. | Fixnum
s | Treat two1 successive characters as a signed short in native byte order. | Fixnum
U | Extract UTF-8 characters as unsigned integers. | Integer
u | Extract a UU-encoded string. | String
V | Treat four characters as an unsigned long in little-endian byte order. | Fixnum
v | Treat two characters as an unsigned short in little-endian byte order. | Fixnum
X | Skip backward one character. | ---
x | Skip forward one character. | ---
Z | String with trailing nulls removed. | String
@ | Skip to the offset given by the length argument. | ---
1 May be modified by appending ``_'' to the directive.
`"abc \0\0abc \0\0".unpack('A6Z6')` | » | `["abc", "abc "]`
`"abc \0\0".unpack('a3a3')` | » | `["abc", " \000\000"]`
`"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"]`
upcase | str.upcase -> aString
|  | Returns a copy of str with all lowercase letters replaced with their uppercase counterparts. The operation is locale insensitive---only characters ``a'' to ``z'' are affected.
`"hEllO".upcase` | » | `"HELLO"`
upcase! | str.upcase! -> str or `nil`
|  | Upcases the contents of str, returning `nil` if no changes were made.
upto | str.upto( aString ) {| s | block } -> str
|  | Iterates through successive values, starting at str and ending at aString inclusive, passing each value in turn to the block. The `String#succ` method is used to generate each value.
    "a8".upto("b6") {|s| print s, ' ' }
    for s in "a8".."b6"
      print s, ' '
    end
produces:
    a8 a9 b0 b1 b2 b3 b4 b5 b6
    a8 a9 b0 b1 b2 b3 b4 b5 b6

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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/)).

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