Ruby: Most concise way to use an ENV variable if it exists, otherwise use default value

Ruby: Most concise way to use an ENV variable if it exists, otherwise use default value

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In Ruby, I am trying to write a line that uses a variable if it has been set, otherwise default to some value:

myvar = # assign it to ENV['MY_VAR'], otherwise assign it to 'foobar'

I could write this code like this:

if ENV['MY_VAR'].is_set? #whatever the function is to check if has been set
  myvar = ENV['MY_VAR']
else
  myvar = 'foobar'
end

But this is rather verbose, and I'm trying to write it in the most concise way possible. How can I do this?


myvar = ENV['MY_VAR'] || 'foobar'

N.B. This is slightly incorrect (if the hash can contain the value nil) but since ENV contains just strings it is probably good enough.

Check for Ruby env variable, In Ruby, I am trying to write a line that uses a variable if it has been set, otherwise default to some value: myvar = # assign it to ENV['MY_VAR'], otherwise assign  0 Ruby: Most concise way to use an ENV variable if it exists, otherwise use default value Jan 9 '19 View all questions and answers → Badges (9)


The most reliable way for a general Hash is to ask if it has the key:

myvar = h.has_key?('MY_VAR') ? h['MY_VAR'] : 'default'

If you don't care about nil or false values (i.e. you want to treat them the same as "not there"), then undur_gongor's approach is good (this should also be fine when h is ENV):

myvar = h['MY_VAR'] || 'foobar'

And if you want to allow nil to be in your Hash but pretend it isn't there (i.e. a nil value is the same as "not there") while allowing a false in your Hash:

myvar = h['MY_VAR'].nil? ? 'foobar' : h['MY_VAR']

In the end it really depends on your precise intent and you should choose the approach that matches your intent. The choice between if/else/end and ? : is, of course, a matter of taste and "concise" doesn't mean "least number of characters" so feel free to use a ternary or if block as desired.

The ENV object in Ruby - rubycademy, Ruby: Most concise way to use an ENV variable if it exists, otherwise use default value (9 answers). Closed 2 years ago. I tried to check for env  4 Ruby nested hash fetching dynamically Oct 6 '11 4 Ruby: Most concise way to use an ENV variable if it exists, otherwise use default value Oct 6 '11 4 Replacing partial regex matches in place with Ruby Dec 12 '11


hash.fetch(key) { default_value }

Will return the value if it exists, and return default_value if the key doesn't exist.

If and Else, value to the AN_ENV_VARIABLE environment variable using the ENV. provide a default value if it doesn't exist using the ENV.fetch method. 3 Ruby: Most concise way to use an ENV variable if it exists, otherwise use default value Mar 9 '18 0 Apache2: PRNG still contains insufficient entropy Nov 5 '19 Badges (5)


Although it's not relevant in the specific example you gave since you're really asking about hash keys, not variables, Ruby does give a way to check variable definition. Use the defined? keyword (it's not a method, but a keyword since it needs special handling by the interpreter), like so:

a = 1
defined? a
  #=> "local-variable"

@a = 2
defined? @a
  #=> "instance-variable"

@@a = 3
defined? @@a
  #=> "class-variable"

defined? blahblahblah
  #=> nil

Hence you could do:

var = defined?(var) ? var : "default value here"

As far as I know, that's the only way other than an ugly begin/rescue/end block to define a variable in the way that you ask without risking a NameError. As I said, this doesn't apply to hashes since:

hash = {?a => 2, ?b => 3}
defined? hash[?c]
  #=> "method"

i.e. you're checking that the method [] is defined rather than the key/value pair you're using it to access.

rubocop-hq/ruby-style-guide: A community-driven Ruby , We saw how variables let us refer to data not yet known to us when we're writing a program. Similarly, if/else statements allow us to create different paths for our end #=> x exists! if x == 1 puts "x is equal to 1" end #=> [branch does not Hint: Use the "AND" operator to join one or more true/false conditions  OS comes under Python’s standard utility modules. This module provides a portable way of using operating system dependent functionality. os.getenv() method in Python returns the value of the environment variable key if it exists otherwise returns the default value. Syntax: os.getenv(key, default = None) Parameters:


myvar = ENV.fetch('MY_VAR') { 'foobar' }

'foobar' being the default if ENV['MY_VAR'] is unset.

class ENV - Documentation for Ruby 2.4.0, style guide. Contribute to rubocop-hq/ruby-style-guide development by creating an account on GitHub. Consistency within one class or method is the most important. Use spaces around the = operator when assigning default values to method parameters: Use &&= to preprocess variables that may or may not exist. In order to set a value to an existing environment variable, we use an assignment expression. For instance, to set the value of the "LANG" variable to "he_IL.UTF-8", we use the following command: LANG=he_IL.UTF-8


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