Ruby strings, symbols, numbers, dates

String

The two classes, String and Symbol, provide the ability to represent text and work with text. The two classes are very different.

String representation

A string is generally wrapped in a set of quotation marks:

"That's a string."
Single quotes are OK:

' I'm also a string '
Double quotes are used when using character interpolation:

Puts "two plus two equals #{2 + 2}"
Puts ' two plus two equals #{2 + 2} '
The contents of the output are:

Two plus two equals 4.
Two plus two equals #{2 + 2}
The difference between a single citation and a double lead in escape:

The

puts backslashes (\) have to is escaped in double quotes.
puts ' can just type \ Once in a single quoted string. '
puts "But whichever type of quotation mark use ..."
puts "... you have to escape its quotation symbol, such as \"."
puts ' that applies to \ ' in single-quoted strings too. '
puts ' backslash-n just looks like \ n between single quotes. '
puts "But it means newline\nin a double-quoted string."
puts ' Same with \ T, which comes out as \ t with single quotes ... '
puts ... but inserts a tab character:\tinside do Uble quotes. "
puts "You can escape the backslash to get \\n and \\t with double quotes." The
output is:

Backslashes (\) have to is escaped in double quotes.
can just type \ Once in a single quoted string.
But whichever type of quotation mark use ...
Have to escape its quotation symbol, such as ".
That's applies to ' in single-quoted strings too.
Backslash-n just looks like \ n between single quotes.
But It means newline
In a double-quoted string.
Same with \ t, which comes out as \ t with single quotes ...
... but inserts a tab character:inside double quotes.
You can escape the backslash. \ t with double quotes.
6:59 * *

7:24 * *

Other Referral mechanisms

There is also a reference mechanism,%char{text}, the following%q generates a single quote character:

Puts%q{you Needn ' t escape apostrophes when using%q.}
Because the string above is not marked with single quotes, the apostrophe in the string does not have to escape.

Double quotes can also be used with%q,%{}. The separator can also be very casual:

%q-a string-
%q/another string/
%[yet another string]
Here document

Here-doc, can be multiple lines of string:

>> Text = <<eom
This is the ' a ' of text.
This is the second line.
Now we ' re done.
EOM
=> ' This is the ' the ' 's ' Text.\nthis is the second line.\nnow we ' re done.\n '
<<eom start, to the end of EOM, EOM is a separator, it can be any string, EOM is the convention, meaning the word "." To align Left, you do not want to align left to add a-:

>> Text = <<-eom
The EOM doesn ' t have to be flush left!
EOM
=> "The EOM doesn ' t have to be flush left!\n"
The default Here-docs, like a double quote string, explains the character interpolation within it, as well as some escape characters, such as \ n or \ t. If you need to make here-doc like a single quote string, you can do this:

>> text = <<-' EOM '
single-quoted!
Note the literal \ n.
and the literal #{2+2}.
EOM
=> "Single-quoted!\nnote the literal \\n.\nAnd the literal \#{2+2}.\n"
>> puts text
single-quoted!
Note the literal \ n.
and the literal #{2+2}.
=> Nil
Try this again:

>> A = <<eom.to_i * 10
5
EOM
=> 50
Try this again:

>> array = [1,2,3,<<eom,4]
This is the Here-doc.
It becomes array[3]
EOM
=> [1, 2, 3, "This is the here-doc.\nit becomes array[3]\n", 4]
As a method parameter:

Do_something_with_args (A, B, <<eom)
Http://some_very_long_url_or_other_text_best_put_on_its_own_line
EOM
String handling

Get and set substring

The [] operator can get a character from a position in a string. An index number is provided, the index number is zero-based, and the index of negative numbers refers to the last forward number from the string.

Try this:

>> string = ' Ruby is a cool language. '
=> "Ruby is a cool language."
>> String[5]
=> "I"
>> string[-12]
=> "O"
Intercept a paragraph and give [] an M parameter:

>> string[5,10]
=> "is a cool"
You can also use a Range object as an argument:

>> string[7..14]
=> "a Cool"
>> String[-12..-3]
=> "Ol Languag"
>> string[-12..20]
=> "Ol Langua"
>> String[15..-1]
=> "Language."
You can also directly give the content of the substring you want to get, if you find it, return to the string, do not find the return nil:

>> string[' Cool Lang ']
=> "Cool Lang"
>> string[' very cool Lang ']
=> Nil
Regular expression:

>> String[/c[ol]+/]
=> "Cool L"
Slice and slice!:

>> string.slice! (' Cool ')
=> "Cool"
>> string
=> "Ruby is a language."
[The]= method can set the found string:

>> string = ' Ruby is a cool language. '
=> "Ruby is a cool language."
>> string[' cool ' = ' great '
=> "Great"
>> string
=> "Ruby is a great language."
>> string[-1] = '! '
=> "!"
>> string
=> "Ruby is a great language!"
>> string[-9..-1] = ' thing to learn '
=> "thing to learn"
>> string
=> "Ruby is a great thing to learn"
Merging strings

>> ' a ' + ' B '
=> "AB"
>> ' a ' + ' B ' + ' C '
=> "ABC"
+ will always get a new string, so try again:

>> str = ' Hi '
=> "HI"
>> str + ' there. '
=> "Hi there."
>> Str
=> "HI"
Try the << method again, it will change the original string:

>> str = ' Hi '
=> "HI"
>> str << ' there. '
=> "Hi there."
>> Str
=> "Hi there."
Merging strings by interpolation

>> str = ' Hi '
=> "HI"
>> "#{str} there."
=> "Hi there."
Interpolation can be any Ruby expression:

>> "The sum is #{2+2}"
=> "The sum is 4"
No, try this again:

>> ' My name is #{
>> class Person
>> Attr_accessor:name
>> End
>> d = person.new
>> d.name = ' David '
>> D.name
>>}. "
=> "My name is David."
A better way: Ruby will call the object's To_s method in interpolation, you can define your own to_s method:

>> class Person
>> Attr_accessor:name
>> def to_s
>> Name
>> End
>> End
=>: to_s
>> David = Person.new
=> #<person:0x007fbde8a195c0>
>> david.name = ' David '
=> "David"
>> "Hello, #{david}!"
=> "Hello, david!"
In the example above, we take David as a interpolation, and the result is that it will call its to_s.

Query string

There are several flavors of the query string, some can give you a response to Boolean values, and some give you a status report of the string in its current state.

Boolean

You can ask if the string contains a substring, use include? , try:

>> string = ' Ruby is a cool language. '
=> "Ruby is a cool language."
>> string.include? (' Ruby ')
=> true
>> string.include? (' Chinese Version ')
=> false
Start: Start_with?, end: End_with?, try again:

>> String.start_with? (' Ruby ')
=> true
>> String.end_with? ("!!!")
=> false
Ask if the string is not in:

>> String.Empty?
=> false
>> "". Empty?
=> true
Content Query

Get the size of the string:

>> string.size
=> 24
Or:

>> String.Length
=> 24
See how many times the specified character appears in the string:

>> string.count (' a ')
=> 3
How many times a range of characters has occurred altogether:

>> string.count (' g-m ')
=> 5
Because it is case sensitive, try again:

>> String.count (' A-Z ')
=> 1
Try this again:

>> string.count (' Aey. ')
=> 10
There are also negative forms, which use ^:

>> string.count (' ^aey. ')
=> 14
>> string.count (' ^g-m ')
=> 19
Change a pattern:

>> string.count (' ag-m ')
=> 8
>> string.count (' ag-m ', ' ^1 ')
=> 8
Query characters in the string index, use index, reverse check, use Rindex:

>> string.index (' cool ')
=> 10
>> string.index (' l ')
=> 13
>> string.rindex (' l ')
=> 15
Use the Ord method to get the ordinal encoding of a character:

>> ' a '. Ord
=> 97
Multiple characters, take only the first character:

>> ' abc '. Ord
=> 97
Turn:

>> 97.CHR
=> "a"
9:46 * * *

String comparisons and order

2016-09-12 08:09 * * *

The String class mixes the comparable module, which defines the <=> method. So you can do this:

>> ' A ' <=> ' B '
=>-1
>> ' B ' > ' A '
=> true
>> ' A ' > ' a '
=> true
>> '. ' > ', '
=> true
The <=> method returns 1 when the object on the right is large, returns 1 when the object is large on the left, and returns 0 when the two objects are equal.

' B ' is greater than ' a ', ' a ' is greater than ' a ', the effect of the order is the character value, ' A ' is a, ' a ' is 65. '. ' is 46, ', ' is 44.

Comparison is equal

The most common method is = =, try:

>> ' string ' = = ' string '
=> true
>> ' string ' = ' house '
=> false
Two ' string ' are different objects, but their contents are the same.

String#eql? Method can also test for equality. It's usually the same as = =. and string#equal? , it is generally compared to two objects that are not the same object.

>> ' a ' = = ' a '
=> true
>> ' a '. eql? (' a ')
=> true
>> ' a '. Equal? (' a ')
=> false
String distortion

String deformation is divided into three main categories: case, format, content distortion.

Case

Try these:

>> string = ' I Love You '
=> "I Love You"
>> String.upcase
=> "I Love You"
>> String.downcase
=> "I Love You"
>> String.swapcase
=> "I Love You"
First Letter Capital Capitalize/capitalize! ：

>> string = ' I love You '
=> "I Love You"
>> string.capitalize
=> "I Love You"
Formatting

The Rjust,ljust method can adjust the size of a string:

>> string = ' I Love You '
=> "I Love You"
>> String.rjust (25)
=> "I Love You"
>> String.ljust (25)
=> "I Love You"
Provide a second parameter to the method:

>> String.rjust (25, '. ')
=> "......... I Love You "
>> String.ljust (25, '-')
=> "I Love You---------------"
Try the Center method:

>> String.center (25, ' * ')
=> "*******i Love you********"
Remove whitespace using the Stip,lstrip,rstrip method:

>> string = ' I Love You '
=> "I Love You"
>> String.strip
=> "I Love You"
>> String.lstrip
=> "I Love You"
>> String.rstrip
=> "I Love You"
Content Distortion

Chop and Chomp methods can erase the end of a string. Chop is an unconditional deletion character, chomp if the directory substring is found at the end, it is deleted. The default chomp is a newline character.

Try:

>> "I Love You". Chop
=> "I Love Yo"
>> "I Love you\n". Chomp
=> "I Love You"
>> "I Love You". Chomp ("U")
=> "I Love Yo"
Try the power of clear:

>> string = "I Love You"
=> "I Love You"
>> String.clear
=> ""
>> string
=> ""
Replace:

>> string = "I ..."
=> "I ..."
>> string.replace ("I Love You")
=> "I Love You"
>> string
=> "I Love You"
Delete, the rule of the parameter is the same as the parameter rule of the Count method:

>> "I Love You". Delete ("Oue")
=> "I Lv Y"
>> "I Love You". Delete ("^o")
=> "Oo"
>> "I Love You". Delete ("A-e", "^c")
=> "I Lov You"
Crypt,des data encryption, its only parameter is a two-digit salt character:

>> "I Love You". Crypt ("34")
=> "342C1RO5Q3YLQ"
Succ

>> "a". succ
=> "B"
>> "abc". SUCC
=> "Abd"
>> "Azz". succ
=> "Baa"
String conversions

The argument is a number in the range 2-36.

>> "To_i" (17)
=> 289
Do not quite understand the meaning of the parameters of the To_i method, is not the parameter represents the number of digits, the system? Base 17? Base 8,base 16, do not know what the meaning of the system.
8-bit: oct,16 bit: Hex

>> "Oct"
=> 64
>> "Hex".
=> 256
To_f, convert to floating-point number, to_s, return receiver, To_sym,intern, convert to symbol.

>> "1.2345". To_f
=> 1.2345
>> "Hello". to_s
=> "Hello"
>> "abc". To_sym
=>: ABC
>> "1.23and some words". To_f
=> 1.23
>> "Just some words". to_i
=> 0
String encoding

Encoding of source files

The default is UTF-8 encoding. To be sure, put the following code in a file and run it again.

Puts __encoding__
To change the encoding of the source file, you can use a magic annotation at the top of the file:

# encoding:encoding
For example, set into Us-ascii:

# ENCODING:ASCII
Encoding of individual strings

>> str = "Test string"
=> "Test String"
>> str.encoding
=> #<encoding:utf-8>
Set string encoding:

>> Str.encode ("Us-ascii")
=> "Test String"
Symbol

The symbol is an instance of Ruby's built-in class symbol. Their literal constructors are preceded by a colon:

: A
: Book
: "Here's how to make a symbol with spaces in it."
To create a symbol by using the To_sym method:

>> "a". To_sym
=>: A
>> "coverting string to symbol with intern ...". Intern
=>: "coverting string to symbol with intern ..."
Convert a symbol to a string:

>>: a.to_s
=> "a"
>>
The main features of the symbol

Symbols are like strings, many times like integers. The main features are: invariance and uniqueness.

Invariance

A symbol cannot be changed as long as it exists.

Uniqueness

You see a symbol: ABC, no matter where you see it, it is the same object.

Do an experiment:

>> "abc". object_id
=> 70179527234100
>> "abc". object_id
=> 70179527221160
>>: abc.object_id
=> 70179535013580
>>: abc.object_id
=> 70179535013580
Symbols and identifiers

The following code contains a symbol object: x, and a local variable identifier s:

s =: X
Ruby's interior uses symbols to track the names of all the variables, methods, and constants that it creates. Check this out:

>> Symbol.all_symbols
=> [: Inspect,: Intern,: object_id, const_missing,: method_missing,
: method_added,: singleton_method_added,: method_removed,
: Singleton_method_removed,
Assign a value to a variable or constant, create a class, or write a method, and the identifier you select will be placed by Ruby in its symbol table. We can verify:

>> Symbol.all_symbols.size
=> 3481
>> ABC = 1
=> 1
>> Symbol.all_symbols.size
=> 3481
>> Symbol.all_symbols.grep (/abc/)
=> [: ABC]
Use of symbols

The most commonly used is the parameter of the method and the hash key.

Symbols as Method parameters

Attr_accessor:name
Attr_reader:age
The Send method can send a message without a point, and it can receive a symbol:

"ABC". Send (: upcase)
Send can also receive a string parameter, such as UpCase. But by giving it a symbol directly, you save Ruby's business, or Ruby converts the string into a symbol internally.

Symbol as hash key

>> M_hash = {: Title => "Beautiful Life": Year => 1997}
=> {:title=> "Beautiful Life",: year=>1997}
>> M_hash[:year]
=> 1997
Roughly the hash, using the string key:

>> M_hash = {"title" => "Beautiful Life", "Year" => 1997}
=> {"title" => "Beautiful Life", "Year" =>1997}
>> m_hash["title"]
=> "Beautiful Life"
The symbol is quicker and looks better as a hash key.

Here's the hash:

has = {: Title => "Beautiful Life": Year => 1997}
Can also be written as:

has = {title: "Beautiful Life", year:1997}
Comparison of strings and symbols

Think of symbols as integers that look like strings.

Numeric objects

In Ruby, numbers are also objects, and you can send messages to them:

>> n = 99.6
=> 99.6
>> m = N.round
=> 100
>> puts M
100
=> Nil
>> x = 12
=> 12
>> if X.zero?
>> puts "x is zero"
>> Else
?> puts "x is not zero"
>> End
X is not zero
=> Nil
Number class

Numeric
Float
Integer
Fixnum
Bignum
Arithmetic

>> 1 + 1
=> 2
>> 10/5
=> 2
>> 16/5
=> 3
>> 10/3.3
=> 3.0303030303030303
>> 1.2 + 3.4
=> 4.6
>> -12--7
=>-5
>> 10% 3
=> 1
hexadecimal integer preceded by 0x:

>> 0x12
=> 18
>> 0x12 + 12
=> 30
The front band 0 is a octal integer:

>> 012
=> 10
>> 012 + 12
=> 22
>> 012 + 0x12
=> 28
Most arithmetic operations are actually methods, because there are grammatical sugars so it looks like an operator, which should have been:

>> 1.+ (1)
=> 2
>> 12./(3)
=> 4
>> -12.-(-7)
=>-5
Time and date

Import Date:

>> require ' date '
=> true
>> date.parse ("April 1705"). England.strftime ("%B%d%Y")
=> "April 13 1705"
There are several classes of processing time and date: Time,date,datetime. Their objects can be called Date/time objects. Use them first to import:

Require ' date '
Require ' time '
The first line provides Date and DateTime classes, and the second line is the time class. In the future, you might combine the classes of date and time together.

Instantiating a Date/time object

Create a Date Object

>> today = Date.today
=> #<date:2016-09-12 ((2457644j,0s,0n), +0s,2299161j) >
>> today.to_s
=> "2016-09-12"
>> puts today
2016-09-12
=> Nil
Use Date.new to create a Date object to provide it with years, months, days:

>> puts Date.new (1959,2,1)
1959-02-01
If you do not provide month and day, the default will be 1.

To create a Date object with parse:

>> puts Date.parse ("2012/7/22")
2012-07-22
>> puts Date.parse ("03/6/9")
2003-06-09
>> puts Date.parse ("33/6/9")
2033-06-09
>> puts Date.parse ("77/6/9")
1977-06-09
>> puts Date.parse ("November 2 2013")
2013-11-02
>> puts Date.parse ("Nov 2 2013")
2013-11-02
>> puts Date.parse ("2 Nov 2013")
2013-11-02
>> puts Date.parse ("2013/11/2")
2013-11-02
Create a Time object

Create Time object: New (also called Now), at,local (also called mktime), parse.

>> time.new
=> 2016-09-12 10:47:31 +0800
>> time.at (100000000)
=> 1973-03-03 17:46:40 +0800
>> Time.mktime (2007,10,3,14,3,6)
=> 2007-10-03 14:03:06 +0800
>> require ' time '
=> false
>> Time.parse ("March, 1985, 10:35 PM")
=> 1985-03-22 22:35:00 +0800
Epoch (midnight on January 1, 1970, GMT)
Creating Date/time Objects

DateTime is a subclass of Date.

>> puts Datetime.new (2009, 1, 2, 3, 4, 5)
2009-01-02t03:04:05+00:00
=> Nil
>> puts DateTime.Now
2016-09-12t10:54:22+08:00
=> Nil
>> puts DateTime.Parse ("October, 1973, 10:34 AM")
1973-10-23t10:34:00+00:00
=> Nil
JD (Julian date), Commercial,strptime
Date/time Query method

>> dt = DateTime.Now
=> #<datetime:2016-09-12t10:57:55+08:00 ((2457644j,10675s,478039000n), +28800s,2299161j) >
>> Dt.year
=> 2016
>> Dt.hour
=> 10
>> Dt.minute
=> 57
>> Dt.second
=> 55
>> T = Time.now
=> 2016-09-12 10:58:12 +0800
>> T.month
=> 9
>> t.sec
=> 12
>> d = date.today
=> #<date:2016-09-12 ((2457644j,0s,0n), +0s,2299161j) >
>> D.day
=> 12
What's the date of the week?

>> d.monday?
=> true
>> d.friday?
=> false
Date/time Method of formatting

All Date/time objects have strftime methods.

>> T = Time.now
=> 2016-09-12 11:08:22 +0800
>> t.strftime ("%y-%m-%d")
=> "16-09-12"
>> t.strftime ("%y-%m-%d")
=> "2016-09-12"
%Y: four-digit years
%y: two-digit years
%B,%B: Short month, long month
%M: Digital Month
%d: day, left with 0
%e: Day
%a,%a: Short day name, Long day name
%h,%i: Hour, 24, 12.
%m: Min
%s: sec
%c:%a%b%d%h:%m:%s%Y
%x:%m/%d/%y
RFC 2822 (email), RFC 2616 (HTTP):

>> Date.today.rfc2822
=> "Mon, Sep 2016 00:00:00 +0000"
>> DateTime.now.httpdate
=> "Mon, Sep 2016 03:15:24 GMT"
Date/time Conversion method

Time has To_date, To_datetime method, date has To_time,to_datetime method, DateTime has To_time,to_date method.

Date/time arithmetic

>> T = Time.now
=> 2016-09-12 11:18:29 +0800
>> t-20
=> 2016-09-12 11:18:09 +0800
>> T + 20
=> 2016-09-12 11:18:49 +0800
Conversion of the Month:

>> dt = DateTime.Now
=> #<datetime:2016-09-12t11:19:25+08:00 ((2457644j,11965s,940690000n), +28800s,2299161j) >
>> puts DT + 100
2016-12-21t11:19:25+08:00
=> Nil
>> puts DT >> 3
2016-12-12t11:19:25+08:00
=> Nil
>> puts DT << 10
2015-11-12t11:19:25+08:00
=> Nil
Days:

>> d = date.today
=> #<date:2016-09-12 ((2457644j,0s,0n), +0s,2299161j) >
>> puts D.next
2016-09-13
=> Nil
>> puts D.next_year
2017-09-12
=> Nil
>> puts D.next_month
2016-10-12
=> Nil
>> puts D.prev_day (10)
2016-09-02
=> Nil
Upto,downto:

>> d = date.today
=> #<date:2016-09-12 ((2457644j,0s,0n), +0s,2299161j) >
>> Next_week = d + 7
=> #<date:2016-09-19 ((2457651j,0s,0n), +0s,2299161j) >
>> D.upto (Next_week) {|date| puts "#{date} is a #{date.strftime ("%A ")}"}
2016-09-12 is a Monday
2016-09-13 is a Tuesday
2016-09-14 is a Wednesday
2016-09-15 is a Thursday
2016-09-16 is a Friday
2016-09-17 is a Saturday
2016-09-18 is a Sunday
2016-09-19 is a Monday
=> #<date:2016-09-12 ((2457644j,0s,0n), +0s,2299161j) >
View Help: Ri Date

11:24 * * * *