Ruby: Can I write multi-line string with no concatenation?

Question

Is there a way to make this look a little better?

conn.exec \'select attr1, attr2, attr3, attr4, attr5, attr6, attr7 \' +
          \'from table1, table2, ta         


        

Answer 1

The Ruby-way (TM) since Ruby 2.3: Use the squiggly HEREDOC <<~ to define a multi-line string with newlines and proper indentation:

conn.exec <<~EOS
            select attr1, attr2, attr3, attr4, attr5, attr6, attr7
            from table1, table2, table3, etc, etc, etc, etc, etc
            where etc etc etc etc etc etc etc etc etc etc etc etc etc
          EOS

# -> "select...\nfrom...\nwhere..."

If proper indentation is not a concern, then single and double quotes can span multiple lines in Ruby:

conn.exec "select attr1, attr2, attr3, attr4, attr5, attr6, attr7 
           from table1, table2, table3, etc, etc, etc, etc, etc, 
           where etc etc etc etc etc etc etc etc etc etc etc etc etc"    

# -> "select...\n           from...\n           where..."
      

If single or double quotes are cumbersome because that would need lots of escaping, then the percent string literal notation % is the most flexible solution:

conn.exec %(select attr1, attr2, attr3, attr4, attr5, attr6, attr7
            from table1, table2, table3, etc, etc, etc, etc, etc
            where (ProductLine = 'R' OR ProductLine = "S") AND Country = "...")
# -> "select...\n            from...\n            where..."

If the aim is to avoid the newlines (which both the squiggly HEREDOC, quotes and the percent string literal will cause), then a line continuation can be used by putting a backslash \ as the last non-whitespace character in a line. This will continue the line and will cause Ruby to concatenate the Strings back to back (watch out for those spaces inside the quoted string):

conn.exec 'select attr1, attr2, attr3, attr4, attr5, attr6, attr7 ' \
          'from table1, table2, table3, etc, etc, etc, etc, etc, ' \
          'where etc etc etc etc etc etc etc etc etc etc etc etc etc'

# -> "select...from...where..."

If you use Rails String.squish will strip the string of leading and trailing space and collapse all consecutive whitespaces (newlines, tabs, and all) into a single space:

conn.exec "select attr1, attr2, attr3, attr4, attr5, attr6, attr7 
           from table1, table2, table3, etc, etc, etc, etc, etc, 
           where etc etc etc etc etc etc etc etc etc etc etc etc etc".squish

# -> "select...attr7 from...etc, where..."

More details:

Ruby HEREDOC Syntax

The Here Document Notation for Strings works is a way to designate long blocks of text inline in code. It is started by << followed by a user-defined String (the End of String terminator). All following lines are concatenated until the End of String terminator is found at the very beginning of a line:

puts < "Text Text Text Text\nBlaBla"

The End of String terminator can be chosen freely, but it is common to use something like "EOS" (End of String) or something that matches the domain of the String such as "SQL".

HEREDOC supports interpolation by default or when the EOS terminator is double quoted:

price = 10
print <<"EOS"  # comments can be put here
1.) The price is #{price}.
EOS
# -> "1.) The price is 10."

Interpolation can be disabled if the EOS terminator is single quoted:

print <<'EOS' # Disabled interpolation
3.) The price is #{price}.
EOS
# -> "3.) The price is #{price}."

One important restriction of the < is that the End of String terminator needs to be at the beginning of the line:

  puts < "....def foo\n......print "foo"\n....end\n..EOS

To get around this, the <<- syntax was created. It allows the EOS terminator to be indented to make the code look nicer. The lines between the <<- and EOS terminator are still used in their full extend including all indentation:

puts <<-EOS # Use <<- to indent End of String terminator
  def foo
    print "foo"
  end
EOS
# -> "..def foo\n....print "foo"\n..end"

Since Ruby 2.3, we now have the squiggly HEREDOC <<~ removes leading whitespace:

puts <<~EOS # Use the squiggly HEREDOC <<~ to remove leading whitespace (since Ruby 2.3!)
  def foo
    print "foo"
  end
EOS
# -> "def foo\n..print "foo"\nend"

Empty lines and lines which only contains tabs and space are ignored by <<~

puts <<~EOS.inspect 
  Hello

    World!
EOS
#-> "Hello\n..World!"

If both tabs and spaces are used, tabs are considered as equal to 8 spaces. If the least-indented line is in the middle of a tab, this tab is not removed.

puts <<~EOS.inspect
One Tab
Two Spaces
EOS
# -> "\tOne Tab\nTwoSpaces"

HEREDOC can do some crazy stuff such as executing commands using backticks:

puts <<`EOC`            
echo #{price}
echo #{price * 2}
EOC

HEREDOC String definitions can be "stacked", which means that the first EOS terminator (EOSFOO below) will end the first string and start the second (EOSBAR below):

print <

I don't think anybody would ever use it as such, but the < is really just a string literal and can be put whereever a string can normally be put:

def func(a,b,c)
  puts a
  puts b
  puts c
end

func(<

If you don't have Ruby 2.3, but Rails >= 3.0 then you can use String.strip_heredoc which does the same as <<~

# File activesupport/lib/active_support/core_ext/string/strip.rb, line 22
class String
  def strip_heredoc
    gsub(/^#{scan(/^[ \t]*(?=\S)/).min}/, "".freeze)
  end
end

puts <<-USAGE.strip_heredoc # If no Ruby 2.3, but Rails >= 3.0
  This command does such and such.

  Supported options are:
    -h         This message
    ...
USAGE

Troubleshooting

If you see errors when Ruby parses your file, then it is most likely that you either have extra leading or trailing spaces with a HEREDOC or extra trailing spaces with a squiggly HEREDOC. For example:

What you see:

database_yml = <<~EOS
  production:
    database: #{fetch(:user)}
    adapter: postgresql
    pool: 5
    timeout: 5000
EOS  

What Ruby tells you:

SyntaxError: .../sample.rb:xx: can't find string "EOS" anywhere before EOF
...sample.rb:xx: syntax error, unexpected end-of-input, expecting `end'

What is at fault:

Spot the extra spaces after the terminating EOS.

Percent String Literals

See RubyDoc for how to use the percentage sign followed by a string in a parentheses pair such as a %(...), %[...], %{...}, etc. or a pair of any non-alphanumeric character such as %+...+

Last Words

Last, to get the answer to the original question "Is there a way to imply concatenation?" answered: Ruby always implies concatenation if two strings (single and double quoted) are found back to back:

puts "select..." 'from table...' "where..."
# -> "select...from table...where..."

The caveat is that this does not work across line-breaks, because Ruby is interpreting an end of statement and the consequitive line of just strings alone on a line doesn't do anything.