Returns the standard output of executing command in a subshell. Standard input, and error are inherited. The special $? variable is set to a Process::Status associated with this execution.

Example:

`echo hi` # => "hi\n"

Terminates execution immediately, printing message to STDERR and then calling exit(status).

Registers the given Proc for execution when the program exits. If multiple handlers are registered, they are executed in reverse order of registration.

def do_at_exit(str1)
  at_exit { print str1 }
end

at_exit { puts "cruel world" }
do_at_exit("goodbye ")
exit

Produces:

goodbye cruel world

Spawns a Fiber to compute &block in the background after delay has elapsed. Access to get is synchronized between fibers. &block is only called once. May be canceled before &block is called by calling cancel.

d = delay(1) { Process.kill(Signal::KILL, Process.pid) }
# ... long operations ...
d.cancel

Terminates execution immediately, returning the given status code to the invoking environment.

Registered at_exit procs are executed.

See also: Process.fork

See also: Process.fork

Spawns a Fiber to compute &block in the background. Access to get is synchronized between fibers. &block is only called once.

f = future { `echo hello` }
# ... other actions ...
f.get # => "hello\n"

Reads a line from STDIN.

See also: IO#gets.

Conditionally spawns a Fiber to run &block in the background. Access to get is synchronized between fibers. &block is only called once. &block doesn't run by default, only when get is called.

l = lazy { expensive_computation }
spawn { maybe_use_computation(l) }
spawn { maybe_use_computation(l) }

Repeatedly executes the block, passing an incremental Int32 that starts with 0.

loop do |i|
  print "#{i}) "
  line = gets
  break unless line
  # ...
end

Pretty prints each object in objects to STDOUT, followed by a newline. Returns objects.

See also: Object#pretty_print(pp).

Pretty prints each object in objects to STDOUT, followed by a newline. Returns objects.

p foo: 23, bar: 42 # => {foo: 23, bar: 42}

See Object#pretty_print(pp)

Pretty prints object to STDOUT followed by a newline. Returns object.

See also: Object#pretty_print(pp).

Prints objects to STDOUT and then invokes STDOUT.flush.

See also: IO#print.

Prints a formatted string to STDOUT.

See also: IO#printf.

Prints a formatted string to STDOUT.

See also: IO#printf.

Prints objects to STDOUT, each followed by a newline.

See also: IO#puts.

Raises the exception.

This will set the exception's callstack if it hasn't been already. Re-raising a previously catched exception won't replace the callstack.

Raises an Exception with the message.

See Random#rand(x).

See Random#rand.

Reads a line from STDIN.

See also: IO#read_line.

Blocks the current fiber forever.

Meanwhile, other ready-to-execute fibers might start their execution.

Blocks the current Fiber for the specified time span.

While this fiber is waiting this time other ready-to-execute fibers might start their execution.

Blocks the current fiber for the specified number of seconds.

While this fiber is waiting this time other ready-to-execute fibers might start their execution.

Spawns a new fiber.

The newly created fiber doesn't run as soon as spawned.

Example:

# Write "1" every 1 second and "2" every 2 seconds for 6 seconds.

ch = Channel(Nil).new

spawn do
  6.times do
    sleep 1
    puts 1
  end
  ch.send(nil)
end

spawn do
  3.times do
    sleep 2
    puts 2
  end
  ch.send(nil)
end

2.times { ch.receive }

Returns a formatted string.

See also: IO#printf.

Returns a formatted string.

See also: IO#printf.

Executes the given command in a subshell. Standard input, output and error are inherited. Returns true if the command gives zero exit code, false otherwise. The special $? variable is set to a Process::Status associated with this execution.

If command contains no spaces and args is given, it will become its argument list.

If command contains spaces and args is given, command must include "${@}" (including the quotes) to receive the argument list.

No shell interpretation is done in args.

Example:

system("echo *")

Produces:

LICENSE shard.yml Readme.md spec src

Prints a series of expressions together with their values. Useful for print style debugging.

a = 1
pp a # => "a # => 1"

pp [1, 2, 3].map(&.to_s) # => "[1, 2, 3].map(&.to_s) # => ["1", "2", "3"]"

Defines a Struct with the given name and properties.

The generated struct has a constructor with the given properties in the same order as declared. The struct only provides getters, not setters, making it immutable by default.

The properties can be type declarations or assignments.

You can pass a block to this macro, that will be inserted inside the struct definition.

record Point, x : Int32, y : Int32

Point.new 1, 2 # => #<Point(@x=1, @y=2)>

An example with the block version:

record Person, first_name : String, last_name : String do
  def full_name
    "#{first_name} #{last_name}"
  end
end

person = Person.new "John", "Doe"
person.full_name # => "John Doe"

An example with type declarations and default values:

record Point, x : Int32 = 0, y : Int32 = 0

Point.new      # => #<Point(@x=0, @y=0)>
Point.new y: 2 # => #<Point(@x=0, @y=2)>

An example with assignments (in this case the compiler must be able to infer the types from the default values):

record Point, x = 0, y = 0

Point.new      # => #<Point(@x=0, @y=0)>
Point.new y: 2 # => #<Point(@x=0, @y=2)>

Spawns a fiber by first creating a Proc, passing the call's expressions to it, and letting the Proc finally invoke the call.

Compare this:

i = 0
while i < 5
  spawn { print(i) }
  i += 1
end
Fiber.yield
# Output: 55555

To this:

i = 0
while i < 5
  spawn print(i)
  i += 1
end
Fiber.yield
# Output: 01234

This is because in the first case all spawned fibers refer to the same local variable, while in the second example copies of i are passed to a Proc that eventually invokes the call.