ruby 学习 -- string --1

# define
french_string = "il \xc3\xa9tait une fois"
long_string = <<EOF
Here is a long string
With many paragraphs
EOF

puts long_string.empty?
puts long_string.include? "many"

puts french_string + long_string

# concatenate
hash = { key1: "val1", key2: "val2" }
string = ""
str2 = ""
hash.each{|k,v| string << k.to_s << " is " << v << "\n" }
hash.each{|k,v| str2 << "#{k}" << " is " << "#{v}" << "\n"}
puts string
puts str2

# join
data = ['', '', '']
s = ''
data.each { |x| s << x << ' and a '}
puts s # => "1 and a 2 and a 3 and a "
puts data.join(' and a ')

# number
number = 5
puts "The number is #{number}." # => "The number is 5."
puts "The number is #{5}." # => "The number is 5."
puts "The number after #{number} is #{number.next}."
# => "The number after 5 is 6."
puts "The number prior to #{number} is #{number-1}."
# => "The number prior to 5 is 4."
puts "We're ##{number}!" # => "We're #5!"

puts "I've set x to #{x = 5; x += 1}."

# Escaping
puts "\#{foo}"
puts '#{foo}'
# puts "#{foo}" # error because no variable of foo defined.

template = 'Oceania has always been at war with %s.'
puts template % 'Eurasia' # => "Oceania has always been at war with Eurasia."

puts 'To 2 decimal places: %.4f' % Math::PI
puts 'Zero-padded: %.3d' % Math::PI

JSP, ASP type

require 'erb'
template = ERB.new %q{Chunky <%= food %>!}
food = "bacon"
puts template.result(binding) # => "Chunky bacon!"
food = "peanut butter"
puts template.result(binding) # => "Chunky peanut butter!"
puts template.result

reverse, reverse!, split

reverse 和 reverse! 的区别：reverse 不改变 string 本身， reverse! 相当于 s=s.reverse

s = ".sdrawkcab si gnirts sihT"
puts s.reverse
puts s
puts s.reverse!
puts s.split(/(\s+)/) # ["This", " ", "string", " ", "is", " ", "backwards."]
puts s.split(/\s+/) # => ["This", "sting", "is", "backwards."]
puts s.split(' ')     # => ["This", "sting", "is", "backwards."]

八进制 和 十六进制 的定义

octal = "\000\001\010\020"
octal.each_byte { |x| puts x }
#
#
#
#
hexadecimal = "\x00\x01\x10\x20"
hexadecimal.each_byte { |x| puts x }
#
#
#
#

This makes it possible to represent UTF-8 characters even when you can’t type them or display them in your terminal.

Try running this program, and then opening the generated file smiley.html in your web browser:

open('smiley.html', 'wb') do |f|
    f << '<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">'
    f << "\xe2\x98\xBA"
end

特殊字符：

"\a" == "\x07" # => true # ASCII 0x07 = BEL (Sound system bell)
"\b" == "\x08" # => true # ASCII 0x08 = BS (Backspace)
"\e" == "\x1b" # => true # ASCII 0x1B = ESC (Escape)
"\f" == "\x0c" # => true # ASCII 0x0C = FF (Form feed)
"\n" == "\x0a" # => true # ASCII 0x0A = LF (Newline/line feed)
"\r" == "\x0d" # => true # ASCII 0x0D = CR (Carriage return)
"\t" == "\x09" # => true # ASCII 0x09 = HT (Tab/horizontal tab)
"\v" == "\x0b" # => true # ASCII 0x0B = VT (Vertical tab)

ruby里，如果是可读的ASCII字符，即使是以十六进制表示，print出来的还是可读字符。不可读，输出的为十六进制（以\x开头）字符表示形式。

"\x10\x11\xfe\xff" # => "\u0010\u0011\xFE\xFF"
"\x48\145\x6c\x6c\157\x0a" # => "Hello\n"

为了避免混淆，统一的，单反斜线由双反斜线表示：\  => \\

"\\".size # => 1
"\\" == "\x5c" # => true
"\\n"[0] == ?\\ # => true
"\\n"[1] == ?n # => true
"\\n" =~ /\n/ # => nil

组合键的表示. =~ 是正则匹配符号。

"\C-a\C-b\C-c" # => "\u0001\u0002\u0003"
"\M-a\M-b\M-c" # => "\xE1\xE2\xE3"

?\C-a # => "\u0001"
?\M-z # => "\xFA"

contains_control_chars = /[\C-a-\C-^]/
'Foobar' =~ contains_control_chars # => nil
"Foo\C-zbar" =~ contains_control_chars # => 3

def snoop_on_keylog(input)
    input.each_char do |b|
        case b
          when ?\C-c; puts 'Control-C: stopped a process?'
          when ?\C-z; puts 'Control-Z: suspended a process?'
          when ?\n; puts 'Newline.'
          when ?\M-x; puts 'Meta-x: using Emacs?'
        end
     end
end

snoop_on_keylog("ls -ltR\003emacsHello\012\370rot13-other-window\012\032")
# Control-C: stopped a process?
# Newline.
# Meta-x: using Emacs?
# Newline.
# Control-Z: suspended a process?

字符串定义

puts "foo\tbar"
# foo bar
puts %{foo\tbar}
# foo bar
puts %Q{foo\tbar}
# foo bar
puts 'foo\tbar'
# foo\tbar
puts %q{foo\tbar}
# foo\tbar

统计单词个数。

class String
    def word_count
        frequencies = Hash.new(0)
        self.downcase.scan(/(\w+([-'.]\w+)*)/) { |word, ignore| frequencies[word] += 1 }
        return frequencies
    end
end
puts %{"The F.B.I. fella--he's quite the man-about-town."}.word_count
# => {"f.b.i"=>1, "fella"=>1, "he's"=>1,
# "quite"=>1, "the"=>2, "man-about-town"=>1}

end with 2.9 cookbook

to be continued...