passing text to alltt embeded in command (extra newline needed)

Question

I wanted to close alltt inside a command (to add some ornaments around the text), but the spaces that were used for putting the monospaced text into columns was not preserved.

I found the solution here: Problem with alltt package when defining new command

It is (in simplified form):

\newenvironment{comm}[1]
{%
    #1%
    \begin{alltt}}
{\end{alltt}}

it works, but I need to put extra newline after \begin:

\begin{comm}

    user:        some-user
    password:    some-password
\end{comm}

Without this newline it looks like this:

This extra newline is not 'eaten' though, it is preserved, so you always have a huge vertial space before actual text. I tried to switch it for for example \null but it didn't work.

I tried to remove % signs and it worked exactly the same way.

This is not a big problem (I hacked it with some vspace), but I would like to know why is it so, because I think it might clarify some matters for me.

Answer 1

The syntax you're using tells LaTeX to look for an argument to the comm environment. Usually arguments are specified in braces, but the rules of TeX allow to specify it without braces: in this case it's the first token following.

So your attempt

\begin{comm}
  user:        some-user
  password:    some-password
\end{comm}

results in u to be the argument.

Since you don't need anything printed before the alltt environment, the solution is to say

\newenvironment{comm}
  {\begin{alltt}}
  {\end{alltt}}

By the way, it's a good idea to provide a proper name instead of using a generic environment, just as you're doing. You may later need to change how the environment must be printed; if you had used alltt everywhere, you'd need to look at each alltt environment in order to see if it is one that needs changes. By assigning a different name you can instead change the definition of comm, which would not affect other environments based on alltt you have in your document.