How do I split a command into several lines and have LaTeX read it as only one line?

Question

For example, I have a command which has a lot of options:

\documentclass[option1,option2,option3,option4,option5,option6,option7]{article}

I want to split it to several lines so I could read the code better:

\documentclass[option1,
               option2,
               option3,
               option4,
               option5,
               option6,
               option7]{article}

What is the proper way to do it?

Answer 1

End each line with a %. This will gobble the line-feed and all whitespace at the beginning of next line. Thus you'd get

\documentclass[option1,%
               option2,%
               option3,%
               option4,%
               option5,%
               option6,%
               option7]{article}

to do what you want it to.

Edited To Add: As Geoffrey points out in a comment to this answer, in this context, this solution is overkill. Using % at the end of a line will always gobble up the newline and the leading whitespace — however, this is (as Geoffrey points out) irrelevant unless in a context where initial whitespace is influential. Thus, in a \documentclass, it can be omitted and Kit's original code used; while in a case like

\begin{tikzpicture}
  \foreach \p/\x/\y in {%
    0/1/2,%
    2/3/4,%
    3/4/5,%
    4/5/6,%
  } {
    \node [coordinate] (p\p) at (\x,\y) {};
  }
% Do stuff with the defined coordinates
\end{tikzpicture}

it becomes relevant, as otherwise the whitespace would be included with the definition of \p, and destroy the crafted coordinate names.

Plenty similar examples outside of TikZ exist — this was the example I could think of the quickest where it becomes relevant.

Answer 2

If you are too lazy to type % at the end of each input line (or you think it looks ugly to do so), then a sneaky trick is to redefine \endlinechar. Another trick is to set the catcode of ^^M to 9 (ignore). In these cases if you do want a space at the end of the line you have to use "%" (space percent) at the line ending.

{%
a%
  b%
     c
d
}

is equivalent to

{\endlinechar=-1
a
  b
    c %
d
}

is equivalent to

{\catcode`\^^M=9
a
  b
    c %
d
}

is equivalent to

{abc d}