Results for: "OptionParser"

EncodingError

EncodingError is the base class for encoding errors.

SystemCallError

SystemCallError is the base class for all low-level platform-dependent errors.

The errors available on the current platform are subclasses of SystemCallError and are defined in the Errno module.

File.open("does/not/exist")

raises the exception:

Errno::ENOENT: No such file or directory - does/not/exist

DateTime

DateTime

A subclass of Date that easily handles date, hour, minute, second, and offset.

DateTime class is considered deprecated. Use Time class.

DateTime does not consider any leap seconds, does not track any summer time rules.

A DateTime object is created with DateTime::new, DateTime::jd, DateTime::ordinal, DateTime::commercial, DateTime::parse, DateTime::strptime, DateTime::now, Time#to_datetime, etc.

require 'date'

DateTime.new(2001,2,3,4,5,6)
                    #=> #<DateTime: 2001-02-03T04:05:06+00:00 ...>

The last element of day, hour, minute, or second can be a fractional number. The fractional number’s precision is assumed at most nanosecond.

DateTime.new(2001,2,3.5)
                    #=> #<DateTime: 2001-02-03T12:00:00+00:00 ...>

An optional argument, the offset, indicates the difference between the local time and UTC. For example, Rational(3,24) represents ahead of 3 hours of UTC, Rational(-5,24) represents behind of 5 hours of UTC. The offset should be -1 to +1, and its precision is assumed at most second. The default value is zero (equals to UTC).

DateTime.new(2001,2,3,4,5,6,Rational(3,24))
                    #=> #<DateTime: 2001-02-03T04:05:06+03:00 ...>

The offset also accepts string form:

DateTime.new(2001,2,3,4,5,6,'+03:00')
                    #=> #<DateTime: 2001-02-03T04:05:06+03:00 ...>

An optional argument, the day of calendar reform (start), denotes a Julian day number, which should be 2298874 to 2426355 or negative/positive infinity. The default value is Date::ITALY (2299161=1582-10-15).

A DateTime object has various methods. See each reference.

d = DateTime.parse('3rd Feb 2001 04:05:06+03:30')
                    #=> #<DateTime: 2001-02-03T04:05:06+03:30 ...>
d.hour              #=> 4
d.min               #=> 5
d.sec               #=> 6
d.offset            #=> (7/48)
d.zone              #=> "+03:30"
d += Rational('1.5')
                    #=> #<DateTime: 2001-02-04%16:05:06+03:30 ...>
d = d.new_offset('+09:00')
                    #=> #<DateTime: 2001-02-04%21:35:06+09:00 ...>
d.strftime('%I:%M:%S %p')
                    #=> "09:35:06 PM"
d > DateTime.new(1999)
                    #=> true

When should you use DateTime and when should you use Time?

It’s a common misconception that William Shakespeare and Miguel de Cervantes died on the same day in history - so much so that UNESCO named April 23 as World Book Day because of this fact. However, because England hadn’t yet adopted the Gregorian Calendar Reform (and wouldn’t until 1752) their deaths are actually 10 days apart. Since Ruby’s Time class implements a proleptic Gregorian calendar and has no concept of calendar reform there’s no way to express this with Time objects. This is where DateTime steps in:

shakespeare = DateTime.iso8601('1616-04-23', Date::ENGLAND)
 #=> Tue, 23 Apr 1616 00:00:00 +0000
cervantes = DateTime.iso8601('1616-04-23', Date::ITALY)
 #=> Sat, 23 Apr 1616 00:00:00 +0000

Already you can see something is weird - the days of the week are different. Taking this further:

cervantes == shakespeare
 #=> false
(shakespeare - cervantes).to_i
 #=> 10

This shows that in fact they died 10 days apart (in reality 11 days since Cervantes died a day earlier but was buried on the 23rd). We can see the actual date of Shakespeare’s death by using the gregorian method to convert it:

shakespeare.gregorian
 #=> Tue, 03 May 1616 00:00:00 +0000

So there’s an argument that all the celebrations that take place on the 23rd April in Stratford-upon-Avon are actually the wrong date since England is now using the Gregorian calendar. You can see why when we transition across the reform date boundary:

# start off with the anniversary of Shakespeare's birth in 1751
shakespeare = DateTime.iso8601('1751-04-23', Date::ENGLAND)
 #=> Tue, 23 Apr 1751 00:00:00 +0000

# add 366 days since 1752 is a leap year and April 23 is after February 29
shakespeare + 366
 #=> Thu, 23 Apr 1752 00:00:00 +0000

# add another 365 days to take us to the anniversary in 1753
shakespeare + 366 + 365
 #=> Fri, 04 May 1753 00:00:00 +0000

As you can see, if we’re accurately tracking the number of solar years since Shakespeare’s birthday then the correct anniversary date would be the 4th May and not the 23rd April.

So when should you use DateTime in Ruby and when should you use Time? Almost certainly you’ll want to use Time since your app is probably dealing with current dates and times. However, if you need to deal with dates and times in a historical context you’ll want to use DateTime to avoid making the same mistakes as UNESCO. If you also have to deal with timezones then best of luck - just bear in mind that you’ll probably be dealing with local solar times, since it wasn’t until the 19th century that the introduction of the railways necessitated the need for Standard Time and eventually timezones.

Time

A Time object represents a date and time:

Time.new(2000, 1, 1, 0, 0, 0) # => 2000-01-01 00:00:00 -0600

Although its value can be expressed as a single numeric (see Epoch Seconds below), it can be convenient to deal with the value by parts:

t = Time.new(-2000, 1, 1, 0, 0, 0.0)
# => -2000-01-01 00:00:00 -0600
t.year # => -2000
t.month # => 1
t.mday # => 1
t.hour # => 0
t.min # => 0
t.sec # => 0
t.subsec # => 0

t = Time.new(2000, 12, 31, 23, 59, 59.5)
# => 2000-12-31 23:59:59.5 -0600
t.year # => 2000
t.month # => 12
t.mday # => 31
t.hour # => 23
t.min # => 59
t.sec # => 59
t.subsec # => (1/2)

Epoch Seconds

Epoch seconds is the exact number of seconds (including fractional subseconds) since the Unix Epoch, January 1, 1970.

You can retrieve that value exactly using method Time.to_r:

Time.at(0).to_r        # => (0/1)
Time.at(0.999999).to_r # => (9007190247541737/9007199254740992)

Other retrieval methods such as Time#to_i and Time#to_f may return a value that rounds or truncates subseconds.

Time Resolution

A Time object derived from the system clock (for example, by method Time.now) has the resolution supported by the system.

Examples

All of these examples were done using the EST timezone which is GMT-5.

Creating a New Time Instance

You can create a new instance of Time with Time.new. This will use the current system time. Time.now is an alias for this. You can also pass parts of the time to Time.new such as year, month, minute, etc. When you want to construct a time this way you must pass at least a year. If you pass the year with nothing else time will default to January 1 of that year at 00:00:00 with the current system timezone. Here are some examples:

Time.new(2002)         #=> 2002-01-01 00:00:00 -0500
Time.new(2002, 10)     #=> 2002-10-01 00:00:00 -0500
Time.new(2002, 10, 31) #=> 2002-10-31 00:00:00 -0500

You can pass a UTC offset:

Time.new(2002, 10, 31, 2, 2, 2, "+02:00") #=> 2002-10-31 02:02:02 +0200

Or a timezone object:

zone = timezone("Europe/Athens")      # Eastern European Time, UTC+2
Time.new(2002, 10, 31, 2, 2, 2, zone) #=> 2002-10-31 02:02:02 +0200

You can also use Time.local and Time.utc to infer local and UTC timezones instead of using the current system setting.

You can also create a new time using Time.at which takes the number of seconds (with subsecond) since the Unix Epoch.

Time.at(628232400) #=> 1989-11-28 00:00:00 -0500

Working with an Instance of Time

Once you have an instance of Time there is a multitude of things you can do with it. Below are some examples. For all of the following examples, we will work on the assumption that you have done the following:

t = Time.new(1993, 02, 24, 12, 0, 0, "+09:00")

Was that a monday?

t.monday? #=> false

What year was that again?

t.year #=> 1993

Was it daylight savings at the time?

t.dst? #=> false

What’s the day a year later?

t + (60*60*24*365) #=> 1994-02-24 12:00:00 +0900

How many seconds was that since the Unix Epoch?

t.to_i #=> 730522800

You can also do standard functions like compare two times.

t1 = Time.new(2010)
t2 = Time.new(2011)

t1 == t2 #=> false
t1 == t1 #=> true
t1 <  t2 #=> true
t1 >  t2 #=> false

Time.new(2010,10,31).between?(t1, t2) #=> true

What’s Here

First, what’s elsewhere. Class Time:

Here, class Time provides methods that are useful for:

Methods for Creating

Methods for Fetching

Methods for Querying

Methods for Comparing

Methods for Converting

Methods for Rounding

For the forms of argument zone, see Timezone Specifiers.

Timezone Specifiers

Certain Time methods accept arguments that specify timezones:

The value given with any of these must be one of the following (each detailed below):

Hours/Minutes Offsets

The zone value may be a string offset from UTC in the form '+HH:MM' or '-HH:MM', where:

Examples:

t = Time.utc(2000, 1, 1, 20, 15, 1) # => 2000-01-01 20:15:01 UTC
Time.at(t, in: '-23:59')            # => 1999-12-31 20:16:01 -2359
Time.at(t, in: '+23:59')            # => 2000-01-02 20:14:01 +2359

Single-Letter Offsets

The zone value may be a letter in the range 'A'..'I' or 'K'..'Z'; see List of military time zones:

t = Time.utc(2000, 1, 1, 20, 15, 1) # => 2000-01-01 20:15:01 UTC
Time.at(t, in: 'A')                 # => 2000-01-01 21:15:01 +0100
Time.at(t, in: 'I')                 # => 2000-01-02 05:15:01 +0900
Time.at(t, in: 'K')                 # => 2000-01-02 06:15:01 +1000
Time.at(t, in: 'Y')                 # => 2000-01-01 08:15:01 -1200
Time.at(t, in: 'Z')                 # => 2000-01-01 20:15:01 UTC

Integer Offsets

The zone value may be an integer number of seconds in the range -86399..86399:

t = Time.utc(2000, 1, 1, 20, 15, 1) # => 2000-01-01 20:15:01 UTC
Time.at(t, in: -86399)              # => 1999-12-31 20:15:02 -235959
Time.at(t, in: 86399)               # => 2000-01-02 20:15:00 +235959

Timezone Objects

The zone value may be an object responding to certain timezone methods, an instance of Timezone and TZInfo for example.

The timezone methods are:

A custom timezone class may have these instance methods, which will be called if defined:

Time-Like Objects

A Time-like object is a container object capable of interfacing with timezone libraries for timezone conversion.

The argument to the timezone conversion methods above will have attributes similar to Time, except that timezone related attributes are meaningless.

The objects returned by local_to_utc and utc_to_local methods of the timezone object may be of the same class as their arguments, of arbitrary object classes, or of class Integer.

For a returned class other than Integer, the class must have the following methods:

For a returned Integer, its components, decomposed in UTC, are interpreted as times in the specified timezone.

Timezone Names

If the class (the receiver of class methods, or the class of the receiver of instance methods) has find_timezone singleton method, this method is called to achieve the corresponding timezone object from a timezone name.

For example, using Timezone:

class TimeWithTimezone < Time
  require 'timezone'
  def self.find_timezone(z) = Timezone[z]
end

TimeWithTimezone.now(in: "America/New_York")        #=> 2023-12-25 00:00:00 -0500
TimeWithTimezone.new("2023-12-25 America/New_York") #=> 2023-12-25 00:00:00 -0500

Or, using TZInfo:

class TimeWithTZInfo < Time
  require 'tzinfo'
  def self.find_timezone(z) = TZInfo::Timezone.get(z)
end

TimeWithTZInfo.now(in: "America/New_York")          #=> 2023-12-25 00:00:00 -0500
TimeWithTZInfo.new("2023-12-25 America/New_York")   #=> 2023-12-25 00:00:00 -0500

You can define this method per subclasses, or on the toplevel Time class.

IO

An instance of class IO (commonly called a stream) represents an input/output stream in the underlying operating system. Class IO is the basis for input and output in Ruby.

Class File is the only class in the Ruby core that is a subclass of IO. Some classes in the Ruby standard library are also subclasses of IO; these include TCPSocket and UDPSocket.

The global constant ARGF (also accessible as $<) provides an IO-like stream that allows access to all file paths found in ARGV (or found in STDIN if ARGV is empty). ARGF is not itself a subclass of IO.

Class StringIO provides an IO-like stream that handles a String. StringIO is not itself a subclass of IO.

Important objects based on IO include:

An instance of IO may be created using:

Like a File stream, an IO stream has:

And like other IO streams, it has:

Extension io/console

Extension io/console provides numerous methods for interacting with the console; requiring it adds numerous methods to class IO.

Example Files

Many examples here use these variables:

# English text with newlines.
text = <<~EOT
  First line
  Second line

  Fourth line
  Fifth line
EOT

# Russian text.
russian = "\u{442 435 441 442}" # => "тест"

# Binary data.
data = "\u9990\u9991\u9992\u9993\u9994"

# Text file.
File.write('t.txt', text)

# File with Russian text.
File.write('t.rus', russian)

# File with binary data.
f = File.new('t.dat', 'wb:UTF-16')
f.write(data)
f.close

Open Options

A number of IO methods accept optional keyword arguments that determine how a new stream is to be opened:

Also available are the options offered in String#encode, which may control conversion between external and internal encoding.

Basic IO

You can perform basic stream IO with these methods, which typically operate on multi-byte strings:

Position

An IO stream has a nonnegative integer position, which is the byte offset at which the next read or write is to occur. A new stream has position zero (and line number zero); method rewind resets the position (and line number) to zero.

The relevant methods:

Open and Closed Streams

A new IO stream may be open for reading, open for writing, or both.

A stream is automatically closed when claimed by the garbage collector.

Attempted reading or writing on a closed stream raises an exception.

The relevant methods:

End-of-Stream

You can query whether a stream is positioned at its end:

You can reposition to end-of-stream by using method IO#seek:

f = File.new('t.txt')
f.eof? # => false
f.seek(0, :END)
f.eof? # => true
f.close

Or by reading all stream content (which is slower than using IO#seek):

f.rewind
f.eof? # => false
f.read # => "First line\nSecond line\n\nFourth line\nFifth line\n"
f.eof? # => true

Line IO

You can read an IO stream line-by-line using these methods:

Each of these reader methods accepts:

For each of these reader methods, reading may begin mid-line, depending on the stream’s position; see Position:

f = File.new('t.txt')
f.pos = 27
f.each_line {|line| p line }
f.close

Output:

"rth line\n"
"Fifth line\n"

You can write to an IO stream line-by-line using this method:

Line Separator

Each of these methods uses a line separator, which is the string that delimits lines:

The default line separator is the given by the global variable $/, whose value is by default "\n". The line to be read next is all data from the current position to the next line separator:

f = File.new('t.txt')
f.gets # => "First line\n"
f.gets # => "Second line\n"
f.gets # => "\n"
f.gets # => "Fourth line\n"
f.gets # => "Fifth line\n"
f.close

You can specify a different line separator:

f = File.new('t.txt')
f.gets('l')   # => "First l"
f.gets('li')  # => "ine\nSecond li"
f.gets('lin') # => "ne\n\nFourth lin"
f.gets        # => "e\n"
f.close

There are two special line separators:

Line Limit

Each of these methods uses a line limit, which specifies that the number of bytes returned may not be (much) longer than the given limit;

A multi-byte character will not be split, and so a line may be slightly longer than the given limit.

If limit is not given, the line is determined only by sep.

# Text with 1-byte characters.
File.open('t.txt') {|f| f.gets(1) }  # => "F"
File.open('t.txt') {|f| f.gets(2) }  # => "Fi"
File.open('t.txt') {|f| f.gets(3) }  # => "Fir"
File.open('t.txt') {|f| f.gets(4) }  # => "Firs"
# No more than one line.
File.open('t.txt') {|f| f.gets(10) } # => "First line"
File.open('t.txt') {|f| f.gets(11) } # => "First line\n"
File.open('t.txt') {|f| f.gets(12) } # => "First line\n"

# Text with 2-byte characters, which will not be split.
File.open('t.rus') {|f| f.gets(1).size } # => 1
File.open('t.rus') {|f| f.gets(2).size } # => 1
File.open('t.rus') {|f| f.gets(3).size } # => 2
File.open('t.rus') {|f| f.gets(4).size } # => 2

Line Separator and Line Limit

With arguments sep and limit given, combines the two behaviors:

Example:

File.open('t.txt') {|f| f.gets('li', 20) } # => "First li"
File.open('t.txt') {|f| f.gets('li', 2) }  # => "Fi"

Line Number

A readable IO stream has a non-negative integer line number.

The relevant methods:

Unless modified by a call to method IO#lineno=, the line number is the number of lines read by certain line-oriented methods, according to the given line separator sep:

A new stream is initially has line number zero (and position zero); method rewind resets the line number (and position) to zero:

f = File.new('t.txt')
f.lineno # => 0
f.gets   # => "First line\n"
f.lineno # => 1
f.rewind
f.lineno # => 0
f.close

Reading lines from a stream usually changes its line number:

f = File.new('t.txt', 'r')
f.lineno   # => 0
f.readline # => "This is line one.\n"
f.lineno   # => 1
f.readline # => "This is the second line.\n"
f.lineno   # => 2
f.readline # => "Here's the third line.\n"
f.lineno   # => 3
f.eof?     # => true
f.close

Iterating over lines in a stream usually changes its line number:

File.open('t.txt') do |f|
  f.each_line do |line|
    p "position=#{f.pos} eof?=#{f.eof?} lineno=#{f.lineno}"
  end
end

Output:

"position=11 eof?=false lineno=1"
"position=23 eof?=false lineno=2"
"position=24 eof?=false lineno=3"
"position=36 eof?=false lineno=4"
"position=47 eof?=true lineno=5"

Unlike the stream’s position, the line number does not affect where the next read or write will occur:

f = File.new('t.txt')
f.lineno = 1000
f.lineno # => 1000
f.gets   # => "First line\n"
f.lineno # => 1001
f.close

Associated with the line number is the global variable $.:

Character IO

You can process an IO stream character-by-character using these methods:

Byte IO

You can process an IO stream byte-by-byte using these methods:

Codepoint IO

You can process an IO stream codepoint-by-codepoint:

What’s Here

First, what’s elsewhere. Class IO:

Here, class IO provides methods that are useful for:

Creating

Reading

Writing

Positioning

Iterating

Settings

Querying

Buffering

Low-Level Access

Other

OpenStruct

An OpenStruct is a data structure, similar to a Hash, that allows the definition of arbitrary attributes with their accompanying values. This is accomplished by using Ruby’s metaprogramming to define methods on the class itself.

Examples 

require "ostruct"

person = OpenStruct.new
person.name = "John Smith"
person.age  = 70

person.name      # => "John Smith"
person.age       # => 70
person.address   # => nil

An OpenStruct employs a Hash internally to store the attributes and values and can even be initialized with one:

australia = OpenStruct.new(:country => "Australia", :capital => "Canberra")
  # => #<OpenStruct country="Australia", capital="Canberra">

Hash keys with spaces or characters that could normally not be used for method calls (e.g. ()[]*) will not be immediately available on the OpenStruct object as a method for retrieval or assignment, but can still be reached through the Object#send method or using [].

measurements = OpenStruct.new("length (in inches)" => 24)
measurements[:"length (in inches)"]       # => 24
measurements.send("length (in inches)")   # => 24

message = OpenStruct.new(:queued? => true)
message.queued?                           # => true
message.send("queued?=", false)
message.queued?                           # => false

Removing the presence of an attribute requires the execution of the delete_field method as setting the property value to nil will not remove the attribute.

first_pet  = OpenStruct.new(:name => "Rowdy", :owner => "John Smith")
second_pet = OpenStruct.new(:name => "Rowdy")

first_pet.owner = nil
first_pet                 # => #<OpenStruct name="Rowdy", owner=nil>
first_pet == second_pet   # => false

first_pet.delete_field(:owner)
first_pet                 # => #<OpenStruct name="Rowdy">
first_pet == second_pet   # => true

Ractor compatibility: A frozen OpenStruct with shareable values is itself shareable.

Caveats

An OpenStruct utilizes Ruby’s method lookup structure to find and define the necessary methods for properties. This is accomplished through the methods method_missing and define_singleton_method.

This should be a consideration if there is a concern about the performance of the objects that are created, as there is much more overhead in the setting of these properties compared to using a Hash or a Struct. Creating an open struct from a small Hash and accessing a few of the entries can be 200 times slower than accessing the hash directly.

This is a potential security issue; building OpenStruct from untrusted user data (e.g. JSON web request) may be susceptible to a “symbol denial of service” attack since the keys create methods and names of methods are never garbage collected.

This may also be the source of incompatibilities between Ruby versions:

o = OpenStruct.new
o.then # => nil in Ruby < 2.6, enumerator for Ruby >= 2.6

Builtin methods may be overwritten this way, which may be a source of bugs or security issues:

o = OpenStruct.new
o.methods # => [:to_h, :marshal_load, :marshal_dump, :each_pair, ...
o.methods = [:foo, :bar]
o.methods # => [:foo, :bar]

To help remedy clashes, OpenStruct uses only protected/private methods ending with ! and defines aliases for builtin public methods by adding a !:

o = OpenStruct.new(make: 'Bentley', class: :luxury)
o.class # => :luxury
o.class! # => OpenStruct

It is recommended (but not enforced) to not use fields ending in !; Note that a subclass’ methods may not be overwritten, nor can OpenStruct’s own methods ending with !.

For all these reasons, consider not using OpenStruct at all.

Set

This library provides the Set class, which implements a collection of unordered values with no duplicates. It is a hybrid of Array’s intuitive inter-operation facilities and Hash’s fast lookup.

The method to_set is added to Enumerable for convenience.

Set is easy to use with Enumerable objects (implementing each). Most of the initializer methods and binary operators accept generic Enumerable objects besides sets and arrays. An Enumerable object can be converted to Set using the to_set method.

Set uses Hash as storage, so you must note the following points:

Comparison

The comparison operators <, >, <=, and >= are implemented as shorthand for the {proper_,}{subset?,superset?} methods. The <=> operator reflects this order, or return nil for sets that both have distinct elements ({x, y} vs. {x, z} for example).

Example 

require 'set'
s1 = Set[1, 2]                        #=> #<Set: {1, 2}>
s2 = [1, 2].to_set                    #=> #<Set: {1, 2}>
s1 == s2                              #=> true
s1.add("foo")                         #=> #<Set: {1, 2, "foo"}>
s1.merge([2, 6])                      #=> #<Set: {1, 2, "foo", 6}>
s1.subset?(s2)                        #=> false
s2.subset?(s1)                        #=> true

Contact

What’s Here

First, what’s elsewhere. Class Set:

In particular, class Set does not have many methods of its own for fetching or for iterating. Instead, it relies on those in Enumerable.

Here, class Set provides methods that are useful for:

Methods for Creating a Set

Methods for Set Operations

Methods for Comparing

Methods for Querying

Methods for Assigning

Methods for Deleting

Methods for Converting

Methods for Iterating

Other Methods

Monitor

Use the Monitor class when you want to have a lock object for blocks with mutual exclusion.

require 'monitor'

lock = Monitor.new
lock.synchronize do
  # exclusive access
end

Pathname

Pathname represents the name of a file or directory on the filesystem, but not the file itself.

The pathname depends on the Operating System: Unix, Windows, etc. This library works with pathnames of local OS, however non-Unix pathnames are supported experimentally.

A Pathname can be relative or absolute. It’s not until you try to reference the file that it even matters whether the file exists or not.

Pathname is immutable. It has no method for destructive update.

The goal of this class is to manipulate file path information in a neater way than standard Ruby provides. The examples below demonstrate the difference.

All functionality from File, FileTest, and some from Dir and FileUtils is included, in an unsurprising way. It is essentially a facade for all of these, and more.

Examples

Example 1: Using Pathname 

require 'pathname'
pn = Pathname.new("/usr/bin/ruby")
size = pn.size              # 27662
isdir = pn.directory?       # false
dir  = pn.dirname           # Pathname:/usr/bin
base = pn.basename          # Pathname:ruby
dir, base = pn.split        # [Pathname:/usr/bin, Pathname:ruby]
data = pn.read
pn.open { |f| _ }
pn.each_line { |line| _ }

Example 2: Using standard Ruby 

pn = "/usr/bin/ruby"
size = File.size(pn)        # 27662
isdir = File.directory?(pn) # false
dir  = File.dirname(pn)     # "/usr/bin"
base = File.basename(pn)    # "ruby"
dir, base = File.split(pn)  # ["/usr/bin", "ruby"]
data = File.read(pn)
File.open(pn) { |f| _ }
File.foreach(pn) { |line| _ }

Example 3: Special features 

p1 = Pathname.new("/usr/lib")   # Pathname:/usr/lib
p2 = p1 + "ruby/1.8"            # Pathname:/usr/lib/ruby/1.8
p3 = p1.parent                  # Pathname:/usr
p4 = p2.relative_path_from(p3)  # Pathname:lib/ruby/1.8
pwd = Pathname.pwd              # Pathname:/home/gavin
pwd.absolute?                   # true
p5 = Pathname.new "."           # Pathname:.
p5 = p5 + "music/../articles"   # Pathname:music/../articles
p5.cleanpath                    # Pathname:articles
p5.realpath                     # Pathname:/home/gavin/articles
p5.children                     # [Pathname:/home/gavin/articles/linux, ...]

Breakdown of functionality

Core methods

These methods are effectively manipulating a String, because that’s all a path is. None of these access the file system except for mountpoint?, children, each_child, realdirpath and realpath.

File status predicate methods

These methods are a facade for FileTest:

File property and manipulation methods

These methods are a facade for File:

Directory methods

These methods are a facade for Dir:

IO

These methods are a facade for IO:

Utilities

These methods are a mixture of Find, FileUtils, and others:

Method documentation

As the above section shows, most of the methods in Pathname are facades. The documentation for these methods generally just says, for instance, “See FileTest.writable?”, as you should be familiar with the original method anyway, and its documentation (e.g. through ri) will contain more information. In some cases, a brief description will follow.

PTY

Creates and manages pseudo terminals (PTYs). See also en.wikipedia.org/wiki/Pseudo_terminal

PTY allows you to allocate new terminals using ::open or ::spawn a new terminal with a specific command.

Example

In this example we will change the buffering type in the factor command, assuming that factor uses stdio for stdout buffering.

If IO.pipe is used instead of PTY.open, this code deadlocks because factor’s stdout is fully buffered.

# start by requiring the standard library PTY
require 'pty'

master, slave = PTY.open
read, write = IO.pipe
pid = spawn("factor", :in=>read, :out=>slave)
read.close     # we dont need the read
slave.close    # or the slave

# pipe "42" to the factor command
write.puts "42"
# output the response from factor
p master.gets #=> "42: 2 3 7\n"

# pipe "144" to factor and print out the response
write.puts "144"
p master.gets #=> "144: 2 2 2 2 3 3\n"
write.close # close the pipe

# The result of read operation when pty slave is closed is platform
# dependent.
ret = begin
        master.gets     # FreeBSD returns nil.
      rescue Errno::EIO # GNU/Linux raises EIO.
        nil
      end
p ret #=> nil

License

© Copyright 1998 by Akinori Ito.

This software may be redistributed freely for this purpose, in full or in part, provided that this entire copyright notice is included on any copies of this software and applications and derivations thereof.

This software is provided on an “as is” basis, without warranty of any kind, either expressed or implied, as to any matter including, but not limited to warranty of fitness of purpose, or merchantability, or results obtained from use of this software.

Ripper

Ripper is a Ruby script parser.

You can get information from the parser with event-based style. Information such as abstract syntax trees or simple lexical analysis of the Ruby program.

Usage

Ripper provides an easy interface for parsing your program into a symbolic expression tree (or S-expression).

Understanding the output of the parser may come as a challenge, it’s recommended you use PP to format the output for legibility.

require 'ripper'
require 'pp'

pp Ripper.sexp('def hello(world) "Hello, #{world}!"; end')
  #=> [:program,
       [[:def,
         [:@ident, "hello", [1, 4]],
         [:paren,
          [:params, [[:@ident, "world", [1, 10]]], nil, nil, nil, nil, nil, nil]],
         [:bodystmt,
          [[:string_literal,
            [:string_content,
             [:@tstring_content, "Hello, ", [1, 18]],
             [:string_embexpr, [[:var_ref, [:@ident, "world", [1, 27]]]]],
             [:@tstring_content, "!", [1, 33]]]]],
          nil,
          nil,
          nil]]]]

You can see in the example above, the expression starts with :program.

From here, a method definition at :def, followed by the method’s identifier :@ident. After the method’s identifier comes the parentheses :paren and the method parameters under :params.

Next is the method body, starting at :bodystmt (stmt meaning statement), which contains the full definition of the method.

In our case, we’re simply returning a String, so next we have the :string_literal expression.

Within our :string_literal you’ll notice two @tstring_content, this is the literal part for Hello, and !. Between the two @tstring_content statements is a :string_embexpr, where embexpr is an embedded expression. Our expression consists of a local variable, or var_ref, with the identifier (@ident) of world.

Resources

Requirements

License

Ruby License.

SocketError

SocketError is the error class for socket.

StringIO

IO streams for strings, with access similar to IO; see IO.

About the Examples

Examples on this page assume that StringIO has been required:

require 'stringio'

StringScanner

StringScanner provides for lexical scanning operations on a String. Here is an example of its usage:

require 'strscan'

s = StringScanner.new('This is an example string')
s.eos?               # -> false

p s.scan(/\w+/)      # -> "This"
p s.scan(/\w+/)      # -> nil
p s.scan(/\s+/)      # -> " "
p s.scan(/\s+/)      # -> nil
p s.scan(/\w+/)      # -> "is"
s.eos?               # -> false

p s.scan(/\s+/)      # -> " "
p s.scan(/\w+/)      # -> "an"
p s.scan(/\s+/)      # -> " "
p s.scan(/\w+/)      # -> "example"
p s.scan(/\s+/)      # -> " "
p s.scan(/\w+/)      # -> "string"
s.eos?               # -> true

p s.scan(/\s+/)      # -> nil
p s.scan(/\w+/)      # -> nil

Scanning a string means remembering the position of a scan pointer, which is just an index. The point of scanning is to move forward a bit at a time, so matches are sought after the scan pointer; usually immediately after it.

Given the string “test string”, here are the pertinent scan pointer positions:

  t e s t   s t r i n g
0 1 2 ...             1
                      0

When you scan for a pattern (a regular expression), the match must occur at the character after the scan pointer. If you use scan_until, then the match can occur anywhere after the scan pointer. In both cases, the scan pointer moves just beyond the last character of the match, ready to scan again from the next character onwards. This is demonstrated by the example above.

Method Categories

There are other methods besides the plain scanners. You can look ahead in the string without actually scanning. You can access the most recent match. You can modify the string being scanned, reset or terminate the scanner, find out or change the position of the scan pointer, skip ahead, and so on.

Advancing the Scan Pointer

Looking Ahead

Finding Where we Are

Setting Where we Are

Match Data

Miscellaneous

There are aliases to several of the methods.

EOFError

Raised by some IO operations when reaching the end of file. Many IO methods exist in two forms,

one that returns nil when the end of file is reached, the other raises EOFError.

EOFError is a subclass of IOError.

file = File.open("/etc/hosts")
file.read
file.gets     #=> nil
file.readline #=> EOFError: end of file reached
file.close

ARGF

ARGF is a stream designed for use in scripts that process files given as command-line arguments or passed in via STDIN.

The arguments passed to your script are stored in the ARGV Array, one argument per element. ARGF assumes that any arguments that aren’t filenames have been removed from ARGV. For example:

$ ruby argf.rb --verbose file1 file2

ARGV  #=> ["--verbose", "file1", "file2"]
option = ARGV.shift #=> "--verbose"
ARGV  #=> ["file1", "file2"]

You can now use ARGF to work with a concatenation of each of these named files. For instance, ARGF.read will return the contents of file1 followed by the contents of file2.

After a file in ARGV has been read ARGF removes it from the Array. Thus, after all files have been read ARGV will be empty.

You can manipulate ARGV yourself to control what ARGF operates on. If you remove a file from ARGV, it is ignored by ARGF; if you add files to ARGV, they are treated as if they were named on the command line. For example:

ARGV.replace ["file1"]
ARGF.readlines # Returns the contents of file1 as an Array
ARGV           #=> []
ARGV.replace ["file2", "file3"]
ARGF.read      # Returns the contents of file2 and file3

If ARGV is empty, ARGF acts as if it contained "-" that makes ARGF read from STDIN, i.e. the data piped or typed to your script. For example:

$ echo "glark" | ruby -e 'p ARGF.read'
"glark\n"

$ echo Glark > file1
$ echo "glark" | ruby -e 'p ARGF.read' -- - file1
"glark\nGlark\n"

ERB

ERB – Ruby Templating

Introduction

ERB provides an easy to use but powerful templating system for Ruby. Using ERB, actual Ruby code can be added to any plain text document for the purposes of generating document information details and/or flow control.

A very simple example is this:

require 'erb'

x = 42
template = ERB.new <<-EOF
  The value of x is: <%= x %>
EOF
puts template.result(binding)

Prints: The value of x is: 42

More complex examples are given below.

Recognized Tags

ERB recognizes certain tags in the provided template and converts them based on the rules below:

<% Ruby code -- inline with output %>
<%= Ruby expression -- replace with result %>
<%# comment -- ignored -- useful in testing %> (`<% #` doesn't work. Don't use Ruby comments.)
% a line of Ruby code -- treated as <% line %> (optional -- see ERB.new)
%% replaced with % if first thing on a line and % processing is used
<%% or %%> -- replace with <% or %> respectively

All other text is passed through ERB filtering unchanged.

Options

There are several settings you can change when you use ERB:

See the ERB.new and ERB#result methods for more detail.

Character encodings

ERB (or Ruby code generated by ERB) returns a string in the same character encoding as the input string. When the input string has a magic comment, however, it returns a string in the encoding specified by the magic comment.

# -*- coding: utf-8 -*-
require 'erb'

template = ERB.new <<EOF
<%#-*- coding: Big5 -*-%>
  \_\_ENCODING\_\_ is <%= \_\_ENCODING\_\_ %>.
EOF
puts template.result

Prints: _ENCODING_ is Big5.

Examples

Plain Text

ERB is useful for any generic templating situation. Note that in this example, we use the convenient “% at start of line” tag, and we quote the template literally with %q{...} to avoid trouble with the backslash.

require "erb"

# Create template.
template = %q{
  From:  James Edward Gray II <james@grayproductions.net>
  To:  <%= to %>
  Subject:  Addressing Needs

  <%= to[/\w+/] %>:

  Just wanted to send a quick note assuring that your needs are being
  addressed.

  I want you to know that my team will keep working on the issues,
  especially:

  <%# ignore numerous minor requests -- focus on priorities %>
  % priorities.each do |priority|
    * <%= priority %>
  % end

  Thanks for your patience.

  James Edward Gray II
}.gsub(/^  /, '')

message = ERB.new(template, trim_mode: "%<>")

# Set up template data.
to = "Community Spokesman <spokesman@ruby_community.org>"
priorities = [ "Run Ruby Quiz",
               "Document Modules",
               "Answer Questions on Ruby Talk" ]

# Produce result.
email = message.result
puts email

Generates:

From:  James Edward Gray II <james@grayproductions.net>
To:  Community Spokesman <spokesman@ruby_community.org>
Subject:  Addressing Needs

Community:

Just wanted to send a quick note assuring that your needs are being addressed.

I want you to know that my team will keep working on the issues, especially:

    * Run Ruby Quiz
    * Document Modules
    * Answer Questions on Ruby Talk

Thanks for your patience.

James Edward Gray II

Ruby in HTML

ERB is often used in .rhtml files (HTML with embedded Ruby). Notice the need in this example to provide a special binding when the template is run, so that the instance variables in the Product object can be resolved.

require "erb"

# Build template data class.
class Product
  def initialize( code, name, desc, cost )
    @code = code
    @name = name
    @desc = desc
    @cost = cost

    @features = [ ]
  end

  def add_feature( feature )
    @features << feature
  end

  # Support templating of member data.
  def get_binding
    binding
  end

  # ...
end

# Create template.
template = %{
  <html>
    <head><title>Ruby Toys -- <%= @name %></title></head>
    <body>

      <h1><%= @name %> (<%= @code %>)</h1>
      <p><%= @desc %></p>

      <ul>
        <% @features.each do |f| %>
          <li><b><%= f %></b></li>
        <% end %>
      </ul>

      <p>
        <% if @cost < 10 %>
          <b>Only <%= @cost %>!!!</b>
        <% else %>
           Call for a price, today!
        <% end %>
      </p>

    </body>
  </html>
}.gsub(/^  /, '')

rhtml = ERB.new(template)

# Set up template data.
toy = Product.new( "TZ-1002",
                   "Rubysapien",
                   "Geek's Best Friend!  Responds to Ruby commands...",
                   999.95 )
toy.add_feature("Listens for verbal commands in the Ruby language!")
toy.add_feature("Ignores Perl, Java, and all C variants.")
toy.add_feature("Karate-Chop Action!!!")
toy.add_feature("Matz signature on left leg.")
toy.add_feature("Gem studded eyes... Rubies, of course!")

# Produce result.
rhtml.run(toy.get_binding)

Generates (some blank lines removed):

<html>
  <head><title>Ruby Toys -- Rubysapien</title></head>
  <body>

    <h1>Rubysapien (TZ-1002)</h1>
    <p>Geek's Best Friend!  Responds to Ruby commands...</p>

    <ul>
        <li><b>Listens for verbal commands in the Ruby language!</b></li>
        <li><b>Ignores Perl, Java, and all C variants.</b></li>
        <li><b>Karate-Chop Action!!!</b></li>
        <li><b>Matz signature on left leg.</b></li>
        <li><b>Gem studded eyes... Rubies, of course!</b></li>
    </ul>

    <p>
         Call for a price, today!
    </p>

  </body>
</html>

Notes

There are a variety of templating solutions available in various Ruby projects. For example, RDoc, distributed with Ruby, uses its own template engine, which can be reused elsewhere.

Other popular engines could be found in the corresponding Category of The Ruby Toolbox.

IPAddr

IPAddr provides a set of methods to manipulate an IP address. Both IPv4 and IPv6 are supported.

Example 

require 'ipaddr'

ipaddr1 = IPAddr.new "3ffe:505:2::1"

p ipaddr1                   #=> #<IPAddr: IPv6:3ffe:0505:0002:0000:0000:0000:0000:0001/ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff>

p ipaddr1.to_s              #=> "3ffe:505:2::1"

ipaddr2 = ipaddr1.mask(48)  #=> #<IPAddr: IPv6:3ffe:0505:0002:0000:0000:0000:0000:0000/ffff:ffff:ffff:0000:0000:0000:0000:0000>

p ipaddr2.to_s              #=> "3ffe:505:2::"

ipaddr3 = IPAddr.new "192.168.2.0/24"

p ipaddr3                   #=> #<IPAddr: IPv4:192.168.2.0/255.255.255.0>

Logger

Class Logger provides a simple but sophisticated logging utility that you can use to create one or more event logs for your program. Each such log contains a chronological sequence of entries that provides a record of the program’s activities.

About the Examples

All examples on this page assume that Logger has been required:

require 'logger'

Synopsis

Create a log with Logger.new:

# Single log file.
logger = Logger.new('t.log')
# Size-based rotated logging: 3 10-megabyte files.
logger = Logger.new('t.log', 3, 10485760)
# Period-based rotated logging: daily (also allowed: 'weekly', 'monthly').
logger = Logger.new('t.log', 'daily')
# Log to an IO stream.
logger = Logger.new($stdout)

Add entries (level, message) with Logger#add:

logger.add(Logger::DEBUG, 'Maximal debugging info')
logger.add(Logger::INFO, 'Non-error information')
logger.add(Logger::WARN, 'Non-error warning')
logger.add(Logger::ERROR, 'Non-fatal error')
logger.add(Logger::FATAL, 'Fatal error')
logger.add(Logger::UNKNOWN, 'Most severe')

Close the log with Logger#close:

logger.close

Entries

You can add entries with method Logger#add:

logger.add(Logger::DEBUG, 'Maximal debugging info')
logger.add(Logger::INFO, 'Non-error information')
logger.add(Logger::WARN, 'Non-error warning')
logger.add(Logger::ERROR, 'Non-fatal error')
logger.add(Logger::FATAL, 'Fatal error')
logger.add(Logger::UNKNOWN, 'Most severe')

These shorthand methods also add entries:

logger.debug('Maximal debugging info')
logger.info('Non-error information')
logger.warn('Non-error warning')
logger.error('Non-fatal error')
logger.fatal('Fatal error')
logger.unknown('Most severe')

When you call any of these methods, the entry may or may not be written to the log, depending on the entry’s severity and on the log level; see Log Level

An entry always has:

And may also have:

Example:

logger = Logger.new($stdout)
logger.add(Logger::INFO, 'My message.', 'mung')
# => I, [2022-05-07T17:21:46.536234 #20536]  INFO -- mung: My message.

The default format for an entry is:

"%s, [%s #%d] %5s -- %s: %s\n"

where the values to be formatted are:

You can use a different entry format by:

Severity

The severity of a log entry has two effects:

Timestamp

The timestamp for a log entry is generated automatically when the entry is created.

The logged timestamp is formatted by method Time#strftime using this format string:

'%Y-%m-%dT%H:%M:%S.%6N'

Example:

logger = Logger.new($stdout)
logger.add(Logger::INFO)
# => I, [2022-05-07T17:04:32.318331 #20536]  INFO -- : nil

You can set a different format using method datetime_format=.

Message

The message is an optional argument to an entry method:

logger = Logger.new($stdout)
logger.add(Logger::INFO, 'My message')
# => I, [2022-05-07T18:15:37.647581 #20536]  INFO -- : My message

For the default entry formatter, Logger::Formatter, the message object may be:

Note: Logger::Formatter does not escape or sanitize the message passed to it. Developers should be aware that malicious data (user input) may be in the message, and should explicitly escape untrusted data.

You can use a custom formatter to escape message data; see the example at formatter=.

Program Name

The program name is an optional argument to an entry method:

logger = Logger.new($stdout)
logger.add(Logger::INFO, 'My message', 'mung')
# => I, [2022-05-07T18:17:38.084716 #20536]  INFO -- mung: My message

The default program name for a new logger may be set in the call to Logger.new via optional keyword argument progname:

logger = Logger.new('t.log', progname: 'mung')

The default program name for an existing logger may be set by a call to method progname=:

logger.progname = 'mung'

The current program name may be retrieved with method progname:

logger.progname # => "mung"

Log Level

The log level setting determines whether an entry is actually written to the log, based on the entry’s severity.

These are the defined severities (least severe to most severe):

logger = Logger.new($stdout)
logger.add(Logger::DEBUG, 'Maximal debugging info')
# => D, [2022-05-07T17:57:41.776220 #20536] DEBUG -- : Maximal debugging info
logger.add(Logger::INFO, 'Non-error information')
# => I, [2022-05-07T17:59:14.349167 #20536]  INFO -- : Non-error information
logger.add(Logger::WARN, 'Non-error warning')
# => W, [2022-05-07T18:00:45.337538 #20536]  WARN -- : Non-error warning
logger.add(Logger::ERROR, 'Non-fatal error')
# => E, [2022-05-07T18:02:41.592912 #20536] ERROR -- : Non-fatal error
logger.add(Logger::FATAL, 'Fatal error')
# => F, [2022-05-07T18:05:24.703931 #20536] FATAL -- : Fatal error
logger.add(Logger::UNKNOWN, 'Most severe')
# => A, [2022-05-07T18:07:54.657491 #20536]   ANY -- : Most severe

The default initial level setting is Logger::DEBUG, the lowest level, which means that all entries are to be written, regardless of severity:

logger = Logger.new($stdout)
logger.level # => 0
logger.add(0, "My message")
# => D, [2022-05-11T15:10:59.773668 #20536] DEBUG -- : My message

You can specify a different setting in a new logger using keyword argument level with an appropriate value:

logger = Logger.new($stdout, level: Logger::ERROR)
logger = Logger.new($stdout, level: 'error')
logger = Logger.new($stdout, level: :error)
logger.level # => 3

With this level, entries with severity Logger::ERROR and higher are written, while those with lower severities are not written:

logger = Logger.new($stdout, level: Logger::ERROR)
logger.add(3)
# => E, [2022-05-11T15:17:20.933362 #20536] ERROR -- : nil
logger.add(2) # Silent.

You can set the log level for an existing logger with method level=:

logger.level = Logger::ERROR

These shorthand methods also set the level:

logger.debug! # => 0
logger.info!  # => 1
logger.warn!  # => 2
logger.error! # => 3
logger.fatal! # => 4

You can retrieve the log level with method level.

logger.level = Logger::ERROR
logger.level # => 3

These methods return whether a given level is to be written:

logger.level = Logger::ERROR
logger.debug? # => false
logger.info?  # => false
logger.warn?  # => false
logger.error? # => true
logger.fatal? # => true

Log File Rotation

By default, a log file is a single file that grows indefinitely (until explicitly closed); there is no file rotation.

To keep log files to a manageable size, you can use log file rotation, which uses multiple log files:

Size-Based Rotation

For size-based log file rotation, call Logger.new with:

Examples:

logger = Logger.new('t.log', 3)           # Three 1-megabyte files.
logger = Logger.new('t.log', 5, 10485760) # Five 10-megabyte files.

For these examples, suppose:

logger = Logger.new('t.log', 3)

Logging begins in the new log file, t.log; the log file is “full” and ready for rotation when a new entry would cause its size to exceed shift_size.

The first time t.log is full:

The second time t.log is full:

Each subsequent time that t.log is full, the log files are rotated:

Periodic Rotation

For periodic rotation, call Logger.new with:

Examples:

logger = Logger.new('t.log', 'daily')   # Rotate log files daily.
logger = Logger.new('t.log', 'weekly')  # Rotate log files weekly.
logger = Logger.new('t.log', 'monthly') # Rotate log files monthly.

Example:

logger = Logger.new('t.log', 'daily')

When the given period expires:

The default format for the suffix is '%Y%m%d', which produces a suffix similar to the one above. You can set a different format using create-time option shift_period_suffix; see details and suggestions at Time#strftime.

FloatDomainError

Raised when attempting to convert special float values (in particular Infinity or NaN) to numerical classes which don’t support them.

Float::INFINITY.to_r   #=> FloatDomainError: Infinity

FalseClass

The global value false is the only instance of class FalseClass and represents a logically false value in boolean expressions. The class provides operators allowing false to participate correctly in logical expressions.

LocalJumpError

Raised when Ruby can’t yield as requested.

A typical scenario is attempting to yield when no block is given:

def call_block
  yield 42
end
call_block

raises the exception:

LocalJumpError: no block given (yield)

A more subtle example:

def get_me_a_return
  Proc.new { return 42 }
end
get_me_a_return.call

raises the exception:

LocalJumpError: unexpected return

SystemStackError

Raised in case of a stack overflow.

def me_myself_and_i
  me_myself_and_i
end
me_myself_and_i

raises the exception:

SystemStackError: stack level too deep

RegexpError

Raised when given an invalid regexp expression.

Regexp.new("?")

raises the exception:

RegexpError: target of repeat operator is not specified: /?/

ThreadError

Raised when an invalid operation is attempted on a thread.

For example, when no other thread has been started:

Thread.stop

This will raises the following exception:

ThreadError: stopping only thread
note: use sleep to stop forever
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