How to capitalize the first letter in a String in Ruby

Question

The upcase method capitalizes the entire string  but I need to capitalize only the first letter   Also  I need to support several popular languages  like German and Russian   How do I do it

User · Answer

Below is another way to capitalize each word in a string. \w doesn't match Cyrillic characters or Latin characters with diacritics but [[:word:]] does. upcase, downcase, capitalize, and swapcase didn't apply to non-ASCII characters until Ruby 2.4.0 which was released in 2016.

"aAa-BBB ä ????? _a a_a".gsub(/\w+/,&:capitalize)
=> "Aaa-Bbb ä ????? _a A_a"
"aAa-BBB ä ????? _a a_a".gsub(/[[:word:]]+/,&:capitalize)
=> "Aaa-Bbb Ä ????? _a A_a"

[[:word:]] matches characters in these categories:

Ll (Letter, Lowercase)
Lu (Letter, Uppercase)
Lt (Letter, Titlecase)
Lo (Letter, Other)
Lm (Letter, Modifier)
Nd (Number, Decimal Digit)
Pc (Punctuation, Connector)

[[:word:]] matches all 10 of the characters in the "Punctuation, Connector" (Pc) category:

005F _ LOW LINE
203F ? UNDERTIE
2040 ? CHARACTER TIE
2054 ? INVERTED UNDERTIE
FE33 ? PRESENTATION FORM FOR VERTICAL LOW LINE
FE34 ? PRESENTATION FORM FOR VERTICAL WAVY LOW LINE
FE4D ? DASHED LOW LINE
FE4E ? CENTRELINE LOW LINE
FE4F ? WAVY LOW LINE
FF3F _ FULLWIDTH LOW LINE

This is another way to only convert the first character of a string to uppercase:

"striNG".sub(/./,&:upcase)
=> "StriNG"

User · Answer

Rails 5   As of Active Support and Rails 5 0 0 beta4 you can use one of both methods  String upcase first or ActiveSupport  Inflector upcase first    my API is great  upcase first    gt   My API is great          upcase first              gt                  upcase first              gt           NASA  upcase first               gt   NASA   MHz  upcase first                gt   MHz   sputnik  upcase first            gt   Sputnik    Check  Rails 5  New upcase first Method  for more info

User · Answer

Well  just so we know how to capitalize only the first letter and leave the rest of them alone  because sometimes that is what is desired     NASA    MHz    sputnik   collect do  word    letters   word split       letters first upcase    letters join end     gt    NASA    MHz    Sputnik     Calling capitalize would result in   Nasa    Mhz    Sputnik

User · Answer

capitalize first letter of first word of string  quot kirk douglas quot  capitalize    gt   quot Kirk douglas quot   capitalize first letter of each word In rails   quot kirk douglas quot  titleize   gt   quot Kirk Douglas quot   OR  quot kirk douglas quot  titleize   gt   quot Kirk Douglas quot       In ruby   quot kirk douglas quot  split        -   map  amp  capitalize  join  quot   quot       gt   quot Kirk Douglas quot   OR require  active support core ext   quot kirk douglas quot  titleize

User · Answer

Use capitalize  From the String documentation      Returns a copy of str with the first character converted to uppercase and the remainder to lowercase       hello  capitalize       gt   Hello   HELLO  capitalize       gt   Hello   123ABC  capitalize      gt   123abc

User · Answer

It depends on which Ruby version you use   Ruby 2 4 and higher   It just works  as since Ruby v2 4 0 supports Unicode case mapping           capitalize    gt          Ruby 2 3 and lower    maria  capitalize    gt   Maria          capitalize    gt          The problem is  it just doesn t do what you want it to  it outputs       instead of         If you re using Rails there s an easy workaround           mb chars capitalize to s   requires ActiveSupport  Multibyte   Otherwise  you ll have to install the unicode gem and use it like this   require  unicode   Unicode  capitalize             gt          Ruby 1 8   Be sure to use the coding magic comment      usr bin env ruby  puts         capitalize   gives invalid multibyte char  US-ASCII   while      usr bin env ruby  coding  utf-8  puts         capitalize   works without errors  but also see the  Ruby 2 3 and lower  section for real capitalization

User · Answer

You can use mb chars  This respects umlaute   class String      Only capitalize first letter of a string   def capitalize first     self 0    self 0  mb chars upcase     self   end  end   Example       mlaute  capitalize first    gt     mlaute

User · Answer

My version  class String     def upcase first         return self if empty          dup tap   s  s 0    s 0  upcase       end     def upcase first          replace upcase first     end end    NASA title    MHz    sputnik   map  amp  upcase first     gt    quot NASA title quot    quot MHz quot    quot Sputnik quot    Check also  https   www rubydoc info gems activesupport 5 0 0 1 String 3Aupcase first https   www rubydoc info gems activesupport 5 0 0 1 ActiveSupport Inflector upcase first-instance method

User · Answer

Unfortunately  it is impossible for a machine to upcase downcase capitalize properly  It needs way too much contextual information for a computer to understand   That s why Ruby s String class only supports capitalization for ASCII characters  because there it s at least somewhat well-defined   What do I mean by  contextual information    For example  to capitalize i properly  you need to know which language the text is in  English  for example  has only two is  capital I without a dot and small i with a dot  But Turkish has four is  capital I without a dot  capital I with a dot  small i without a dot  small i with a dot  So  in English  i  upcase     gt   I  and in Turkish  i  upcase     gt   I   In other words  since  i  upcase can return two different results  depending on the language  it is obviously impossible to correctly capitalize a word without knowing its language   But Ruby doesn t know the language  it only knows the encoding  Therefore it is impossible to properly capitalize a string with Ruby s built-in functionality   It gets worse  even with knowing the language  it is sometimes impossible to do capitalization properly  For example  in German   Ma  e  upcase     gt   MASSE   Ma  e is the plural of Ma   meaning measurement   However   Masse  upcase     gt   MASSE   meaning mass   So  what is  MASSE  capitalize  In other words  correctly capitalizing requires a full-blown Artificial Intelligence   So  instead of sometimes giving the wrong answer  Ruby chooses to sometimes give no answer at all  which is why non-ASCII characters simply get ignored in downcase upcase capitalize operations   Which of course also reads to wrong results  but at least it s easy to check

[ruby] How to capitalize the first letter in a String in Ruby

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