Here-Docs with if then else statement

Question

Like the title says. Is it possible to use an if/then statement in a here-doc for ruby.

Thanks

Answer 1

Compare (and contrast) these samples. Which is more readable, has clearer logic, and would you want to support?:

Example #1:

string = <<END_STRING
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
#{
if (true_or_false)
  'jackdaws love my giant sphinx of quartz'
else
  'Sphinx of black quartz, judge my vow.'
end
}
proident, sunt in culpa qui officia deserunt mollit anim id est laborum. Lorem
ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor
incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore
eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt
in culpa qui officia deserunt mollit anim id est laborum.
END_STRING

Example #2:

string = <<END_STRING
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
#{
(true_or_false) \
  ?  'jackdaws love my giant sphinx of quartz' \
  : 'Sphinx of black quartz, judge my vow.'
}
proident, sunt in culpa qui officia deserunt mollit anim id est laborum. Lorem
ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor
incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore
eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt
in culpa qui officia deserunt mollit anim id est laborum.
END_STRING

Example #3:

string = <<END_STRING
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
#{(true_or_false) ? 'jackdaws love my giant sphinx of quartz' : 'Sphinx of black quartz, judge my vow.'}
proident, sunt in culpa qui officia deserunt mollit anim id est laborum. Lorem
ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor
incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore
eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt
in culpa qui officia deserunt mollit anim id est laborum.
END_STRING

Example #4:

insert_string = (true_or_false) \
  ? 'jackdaws love my giant sphinx of quartz' \
  : 'Sphinx of black quartz, judge my vow.'

string = <<END_STRING
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
${ insert_string }
proident, sunt in culpa qui officia deserunt mollit anim id est laborum. Lorem
ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor
incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore
eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt
in culpa qui officia deserunt mollit anim id est laborum.
END_STRING

Personally I prefer #4 because it separates the logic from the definition of the string, helping to keep it easier to see what is going on, but your mileage might vary.

Answer 2

Yes

---

irb(main):001:0> x = <<-E
irb(main):002:0" How
irb(main):003:0" now
irb(main):004:0" #{
irb(main):005:0"   if true
irb(main):006:0"     "brown"
irb(main):007:0"   else
irb(main):008:0"     "red"
irb(main):009:0"   end
irb(main):010:0" } cow
irb(main):011:0" E
=> "How\nnow\nbrown cow\n"
irb(main):012:0> puts x
How
now
brown cow

Answer 3

A heredoc is just like a string. So if your string allows variable evaluation and substitution (using no quotes or double quotes), you can do something like this:

switcheroo=true
mydoc = <<HDOC
This string will always appear
#{"This will only appear if switcheroo is true" if switcheroo} 
HDOC

You have to put your conditions inside the brackets, standard in-string evaluation technique.

Please also note that this won't work if the quoting for your heredoc uses single quotes, meaning it's a literal string.