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#[]=.
Comparable<, <=, ==, >=, >, between?Enumerablecollect, detect, each_with_index, entries, find, find_all, grep, include?, map, max, member?, min, reject, select, sort, to_aArray containing the values to be substituted. See Kernel::sprintf for details of the format string.
"%05d" % 123 → "00123"
"%-5s: %08x" % [ "ID", self.id ] → "ID‿‿‿:‿200e1670"String containing anInteger copies of
the receiver.
"Ho! " * 3 → "Ho! Ho! Ho! "String containing
aString concatenated to str.
"Hello from " + self.to_s → "Hello from main"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!"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" → 0true or falseString, returns
false. Otherwise, returns true if str <=>
anObject returns zero.
true or falseString#==.
nilRegexp 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 → falsenilnilnilnilnilElement 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"] → nilElement 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"nil =~ str.
"hello".capitalize → "Hello"
"HELLO".capitalize → "Hello"
"123ABC".capitalize → "123abc"nilnil if
no changes are made.
a = "hello"
a.capitalize! → "Hello"
a → "Hello"
a.capitalize! → nilString of length anInteger with str centered
between spaces; otherwise,
returns str.
"hello".center(4) → "hello"
"hello".center(20) → "‿‿‿‿‿‿‿hello‿‿‿‿‿‿‿‿"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"nilString#chomp,
returning str, or nil if no modifications were made.
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 → ""nilString#chop, returning str,
or nil if str is the empty string. See also
String#chomp!.
String#<<.
a = "hello world"
a.count "lo" → 5
a.count "lo", "o" → 2
a.count "hello", "^l" → 4
a.count "ej-m" → 4crypt. The argument is the salt string, which should be two characters long, each character drawn from [a-zA-Z0-9./].
String#count.
"hello".delete "l","lo" → "heo"
"hello".delete "lo" → "he"
"hello".delete "aeiou", "^e" → "hell"
"hello".delete "ej-m" → "ho"nildelete operation in place, returning str, or nil if str was not modified."hEllO".downcase → "hello"nilnil if no
changes were made.
\nnn notation and all special characters
escaped.
\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""hello".each_byte {|c| print c, ' ' }produces:
104 101 108 108 111String#each.
true or falsetrue if str has a length of zero.
"hello".empty? → false
"".empty? → trueReturns 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.
| 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 "nilnilString#gsub in place, returning str, or nil if no substitutions were performed.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'] → nil0x) and
returns the corresponding number. Zero is returned on error.
"0x0a".hex → 10
"-1234".hex → -4660
"0".hex → 0
"wombat".hex → 0true or falsetrue or falsetrue if str contains the given string or character.
"hello".include? "lo" → true
"hello".include? "ol" → false
"hello".include? ?h → truenilnilnilnil 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) → 4Symbol corresponding to str, creating the symbol if it did not previously exist. See Symbol#id2name.
"Koala".intern → :KoalaString of length anInteger with str left
justified and space padded; otherwise, returns str.
"hello".ljust(4) → "hello"
"hello".ljust(20) → "hello‿‿‿‿‿‿‿‿‿‿‿‿‿‿‿"String#succ.
String#succ!.
"123".oct → 83
"-377".oct → -255
"bad".oct → 0
"0377bad".oct → 255s = "hello" → "hello"
s.replace "world" → "world""stressed".reverse → "desserts"nilnilnilnil 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) → 1String of length
anInteger with str right justified and space padded;
otherwise, returns str.
"hello".rjust(4) → "hello"
"hello".rjust(20) → "‿‿‿‿‿‿‿‿‿‿‿‿‿‿‿hello"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"]]a.scan(/\w+/) {|w| print "<<#{w}>> " }
print "\n"
a.scan(/(.)(.)/) {|a,b| print b, a }
print "\n"produces:
<<cruel>> <<world>>
rceu lowlrString#length.
nilnilnilnilnilString#[ ].
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") → nilnilnilnilnilnilFixnum 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"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", "", ""]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"nilnil if no changes were made.
" hello ".strip → "hello"
"\tgoodbye\r\n".strip → "goodbye"nilnil if str was not altered.
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 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"nilnilString#sub in place,
returning str, or nil if no substitutions were
performed.
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 → "**+"String#succ, but modifies the receiver in place.
"Hello".swapcase → "hELLO"
"cYbEr_PuNk11".swapcase → "CyBeR_pUnK11"nilString#swapcase, but modifies the receiver in place, returning str, or nil if no changes were made.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 → 0.00 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 → 0String#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.
^,
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"nilString#tr. Returns str, or nil if no changes were
made.
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"nilString#tr_s processing on str in place,
returning str, or nil if no changes were made.
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. 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.
| Format | Function | Returns |
|---|---|---|
| 1 May be modified by appending “_” to the directive. | ||
| 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. | — |
"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"]"hEllO".upcase → "HELLO"nilnil if no changes were made.String#succ method is used to generate each value.
"a8".upto("b6") {|s| print s, ' ' }
for s in "a8".."b6"
print s, ' '
endproduces:
a8 a9 b0 b1 b2 b3 b4 b5 b6
a8 a9 b0 b1 b2 b3 b4 b5 b6Extracted 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/).
Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder.
Distribution of the work or derivative of the work in any standard (paper) book form is prohibited unless prior permission is obtained from the copyright holder.