How do I dump an object's fields to the console?

Question

When I'm running a simple Ruby script, what's the easiest way to dump an object's fields to the console?

I'm looking for something similar to PHP's print_r() that will work with arrays as well.

Fabrizio

Answer 1

Possibly:

puts variable.inspect

Hege

Adding an inspect method to your class allows you to define how the class' attributes are displayed, rather than rely on default output. A lot of classes don't implement it well, but it can be really useful when debugging. Ruby will fall back to to_s if it can't find an inspect` method. – Litt

Current link is broken, See this one ruby-doc.org/core-2.0/Object.html#method-i-inspect – Schnurr

server = TCPServer.new 0 ; puts server.inspect #<TCPServer:fd 9> => nil . it won't work for most complex objects. – Harday

As this is the first answer found when looking for a php var_dump equivalent in ruby, i found that pp is much usaful in that case, look here - https://mcmap.net/q/100949/-ruby-inspect-readability/… – Orthopter

Note that p object is an alias for puts object.inspect – Neanderthal

inspect works great for attributes, but @dylanfm's answer is better if you want to see methods – Nightlong

Answer 2

You might find a use for the methods method which returns an array of methods for an object. It's not the same as print_r, but still useful at times.

>> "Hello".methods.sort
=> ["%", "*", "+", "<", "<<", "<=", "<=>", "==", "===", "=~", ">", ">=", "[]", "[]=", "__id__", "__send__", "all?", "any?", "between?", "capitalize", "capitalize!", "casecmp", "center", "chomp", "chomp!", "chop", "chop!", "class", "clone", "collect", "concat", "count", "crypt", "delete", "delete!", "detect", "display", "downcase", "downcase!", "dump", "dup", "each", "each_byte", "each_line", "each_with_index", "empty?", "entries", "eql?", "equal?", "extend", "find", "find_all", "freeze", "frozen?", "grep", "gsub", "gsub!", "hash", "hex", "id", "include?", "index", "inject", "insert", "inspect", "instance_eval", "instance_of?", "instance_variable_defined?", "instance_variable_get", "instance_variable_set", "instance_variables", "intern", "is_a?", "is_binary_data?", "is_complex_yaml?", "kind_of?", "length", "ljust", "lstrip", "lstrip!", "map", "match", "max", "member?", "method", "methods", "min", "next", "next!", "nil?", "object_id", "oct", "partition", "private_methods", "protected_methods", "public_methods", "reject", "replace", "respond_to?", "reverse", "reverse!", "rindex", "rjust", "rstrip", "rstrip!", "scan", "select", "send", "singleton_methods", "size", "slice", "slice!", "sort", "sort_by", "split", "squeeze", "squeeze!", "strip", "strip!", "sub", "sub!", "succ", "succ!", "sum", "swapcase", "swapcase!", "taguri", "taguri=", "taint", "tainted?", "to_a", "to_f", "to_i", "to_s", "to_str", "to_sym", "to_yaml", "to_yaml_properties", "to_yaml_style", "tr", "tr!", "tr_s", "tr_s!", "type", "unpack", "untaint", "upcase", "upcase!", "upto", "zip"]

Astronomical

Using introspection is part of the fun of Ruby. It's often useful to subtract an Object's instance_methods from the class' in question to get the methods that are unique: (String.instance_methods - Object.instance_methods).sort – Litt

this should be the correct answer as I was expecting this when finding this page. – Hypophyge

.methods.sort is very useful. Is there any 'smart' way to quickly show methods that are (vaguely) unique to that particular object? E.g. a method like .to_s might show up often so it's not all that useful, but some it could be very handy to know of certain methods for certain objects. Especially in cases that aren't obvious. Is there any way to quickly get these? (case in point, I have a PG::Result object, and want to quickly assess the likely methods I could possibly find useful. – Wrath

You can also distinguish between private_methods, public_methods, and protected_methods, if helpful (as well as private_instance_methods, public_instance_methods, protected_instance_methods). – Nightlong

Answer 3

The to_yaml method seems to be useful sometimes:

$foo = {:name => "Clem", :age => 43}

puts $foo.to_yaml

returns

--- 
:age: 43
:name: Clem

(Does this depend on some YAML module being loaded? Or would that typically be available?)

Somnolent

Yes, to_yaml requires the YAML model to be loaded. It is part of the Ruby standard library, though. – Blane

this was helpful when I was trying to inspect an Amazon S3 object in a Rails app console. – Benitabenites

+1 because to_yaml is much prettier than inspect, -1 because to_yaml doesn't include anything about methods (class or instance) – Nightlong

Answer 4

p object

Ruby doc for p.

p(*args) public

For each object, directly writes obj.inspect followed by a newline to the program’s standard output.

Giltzow

Isn't that the same as variable.to_s? I've found that just prints an object reference unless the class explicitly overrides it – Fabrizio

Answer 5

If you're looking for just the instance variables in the object, this might be useful:

obj.instance_variables.each do |var|
  puts [var, obj.instance_variable_get(var).inspect].join(":")
end

or as a one-liner for copy and pasting:

obj.instance_variables.each{ |var| puts [var, obj.instance_variable_get(var).inspect].join(":")}

Korea

Answer 6

puts foo.to_json

might come in handy since the json module is loaded by default

Gnathonic

to_json isn't loaded by default in 1.8.7 or 1.9.2. – Litt

Answer 7

If you want to print an already indented JSON:

require 'json'
...
puts JSON.pretty_generate(JSON.parse(object.to_json))

Increasing

Answer 8

I came across this thread because I was looking for something similar. I like the responses and they gave me some ideas so I tested the .to_hash method and worked really well for the use case too. soo:

object.to_hash

Goosestep

Answer 9

object.attribute_names

# => ["id", "name", "email", "created_at", "updated_at", "password_digest", "remember_token", "admin", "marketing_permissions", "terms_and_conditions", "disable", "black_list", "zero_cost", "password_reset_token", "password_reset_sent_at"]


object.attributes.values

# => [1, "tom", "[email protected]", Tue, 02 Jun 2015 00:16:03 UTC +00:00, Tue, 02 Jun 2015 00:22:35 UTC +00:00, "$2a$10$gUTr3lpHzXvCDhVvizo8Gu/MxiTrazOWmOQqJXMW8gFLvwDftF9Lm", "2dd1829c9fb3af2a36a970acda0efe5c1d471199", true, nil, nil, nil, nil, nil, nil, nil] 

Crosspiece

undefined method 'attributes' for ... – Cathar

object.attributes_name didn't work, but object.attributes does to get a nice hash of keys and values. This helped me out, thanks! – Churn

Answer 10

pp File.stat('/tmp')

#<File::Stat
 dev=0x1000004,
 ino=71426291,
 mode=041777 (directory rwxrwxrwt),
 nlink=15,
 uid=0 (root),
 gid=0 (wheel),
 rdev=0x0 (0, 0),
 size=480,
 blksize=4096,
 blocks=0,
 atime=2021-04-20 17:50:33.062419819 +0800 (1618912233),
 mtime=2021-04-21 11:35:32.808546288 +0800 (1618976132),
 ctime=2021-04-21 11:35:32.808546288 +0800 (1618976132)>

Helvetia

It is better if you can provide some context to your answer so that other users can understand your approach easily. – Pompidou

Answer 11

I'm using own solution to print and debug variables is https://github.com/igorkasyanchuk/wrapped_print

you can simply call user.wp to see in the logs a value of this variable

instead of:

puts "-"*10
puts user.inspect
puts "-"*10

Penton