17-Jun-15 Assorted Ruby Details. The command line irb starts an interactive Ruby interpreter ruby...

Apr 18, 2023

Assorted Ruby Details

The command line

irb starts an interactive Ruby interpreter ruby starts Ruby, with input from the command line

End with an end-of-file character (^D or F6) Not actually very useful

ruby filename.rb executes the given file ruby -e quotedString executes the quoted string

Example: ruby -e 'puts "The time is #{Time.now}" '

ruby -v tells you Ruby’s version number On Unix, if the first line of a Ruby file is

#!/usr/bin/ruby (or wherever ruby is located), the file can be executed by just entering the file name

Adding and removing methods

def adds a method; undef removes a method The only parameter to undef is the method name

To add an instance method, first “open” the class Example: class String; def nchars; length; end; end

There are several ways to add a class method to a class def Person.species; 'human'; end Within the Person class, you can use def self.species

You can add a method to individual objects def oscar.mood; 'grouchy' ; end

Numbers

Numbers may be written in decimal, hexadecimal, octal, or binary Decimal: 3405691582 Hex: 0xCAFEBABE or 0XCAFEBABE Octal: 031277535276 or 0o31277535276 Binary: 0b11001010111111101011101010111110

or 0Betc. For readability, numbers may contain (but not begin or

end with) underscores Examples: 3_405_691_582, 0b_111_101_101

Integers may be indexed to retrieve their bits Example: 5.step(0, -1) { |i| print 6[i] } 000110

printf and friends

printf format_string, value, …, value Formats are % length code for most things,

% length.fractional_digits code for floats %d decimal, %o octal, %x hex, %b binary,

%f float, %s string Negative lengths mean left justified Various other controls

Example: printf "pi = %8.4f", 3.141592 pi.=…3.1416

The (equivalent) methods sprintf and format take the same parameters as printf, but return the resultant string rather than printing it

Some File < IO methods gets – get a line of text getc – get a character of text (as ASCII; use .chr) ungetc – put back a character pos – the current character position in the input stream lineno – the number of times gets has been called pos= – move to the given position in the file rewind – move to the beginning of the file readlines – read the stream as an array of strings write(string), print(string), <<(string) – write at the current

position eof? – test if at the end of file closed? – test if the file has been closed

Some File methods rename(oldname, newname) – rename a file read(filename) – read the entire file as a single string readlines(filename) – read the entire file as an array of strings open(filename) –

with no block, a synonym for File.new with a block, the file is passed to the block, and automatically closed when

the block finishes exists?(filename) – test if a file with that name exists writable?(filename) – test if the file can be written directory?(filename) – test if the file is a directory zero?(filename) – test if the file is empty size(filename) – returns the size of the file mtime(filename) – returns the modification time of the file

Streams

The following constants refer to standard I/O streams: STDIN, STDOUT, STDERR

The following variables are initially set to the corresponding constants: $stdin, $stdout, $stderr

In addition, $defout (initially equal to $stdout) is where output with no specified destination is sent

Some String methods

ljust(length), center(length), rjust(length) – left justify, center, or right justify the string by padding with spaces

downcase, upcase, swap, capitalize – modify capitalization

include?(s_or_c) – tests whether the string includes the given string or character

index(s_or_c [, offset]) – returns the index after offset(or nil) at which the gives string starts

rindex(s_or_c [, limit]) – returns the last index (before limit), or nil, at which the string starts

Some more String methods

strip – remove leading and trailing spaces chop – remove the last character (also chop! is

destructive) chomp – remove the last character if it is a newline

(also chomp!) tr(chars, replacement) – replace the characters in

chars with the corresponding characters in replacement; accepts ch1-ch2 notation

Some Array methods

min, max – return the smallest or largest element uniq – return an array with no duplicate elements compact – return an array with no nil elements sort – return a sorted array & – perform an intersection (only elements in both) | – perform a union (elements in either) grep(regexp) – return elements matching the pattern push(element) – add the element to the end of the array pop – remove and return the last element shift – remove and return the first element

Chaining

Nondestructive methods can usually be chained Example: x = gets.chomp.strip.downcase

Many destructive methods return nil if they make no changes in the receiver, hence cannot be chained Example: x = gets.chomp!.strip!.downcase! will

result in a runtime error

Iterators

In Ruby, loops are considered low-level, to be used only when there is no appropriate iterator

collection.each – step through every element n.times – do a block n times n.downto(limit) – step from n down to and including

limit n.upto(limit) – step from n up to and including limit string.each_line – get each line from a string string.each_char – get each character (as an integer)

from a string

More iterators

collection.each_index – iterate over the indices of a collection collection.each_with_index – iterate over the values in a

collection, along with their indices Example: lineup.each_with_index { |man, pos| print pos, man }

hash.each_key – iterate over keys hash.each_value – iterate over values hash.each_pair – iterate over key-value pairs collection.select { |v| condition } – choose only items that meet

the condition collection.map { |v| transformation } – create a new collection

with the transformation applied to each item

The End