How to define a command that returns different commands based on a parameter

Question

I would like to define a command \mycommand such that \mycommand{X} produces \Xfirst\Xsecond\label{Xlabel}, where \Xfirst and \Xsecond are already defined commands. Of course, \mycommand{Y} should produce \Yfirst\Ysecond\label{Ylabel}, and \mycommand{Z} should produce what you expected, and so on. For instance, if I have

\newcommand{\Xfirst}{A}
\newcommand{\Xsecond}{xx}
\newcommand{\Yfirst}{B}
\newcommand{\Ysecond}{yy}

then using the command \mycommand{X} must be equivalent to writing Axx\label{Xlabel}, while writing \mycommand{Y} must be equivalent to writing Byy\label{Ylabel}. I think I can do it with (a lot of) ifs. Is there a more elegant form? How? Package hyperref should work well with the generated label.

An example following the suggestion of Ryan Reich (wrong link with hyperref).

\documentclass{article}
\usepackage{hyperref}
\newcommand{\Xfirst}{A}
\newcommand{\Xsecond}{xx}
\newcommand{\Yfirst}{B}
\newcommand{\Ysecond}{yy}
\newcommand\mycommand[1]{%
 \csname #1first\endcsname
 \csname #1second\endcsname
 \label{#1label}%
}
\begin{document}
    \section{Section}
    \mycommand{X}
    \pageref{Ylabel} % does not point to page 3
    \newpage
    Nothing.
    \newpage
    \mycommand{Y}
    \pageref{Xlabel}
\end{document}

Another attempt, using hypertarget and hyperlink. It seems to work.

\documentclass{article}
\usepackage{hyperref}
\newcommand{\Xfirst}{A}
\newcommand{\Xsecond}{xx}
\newcommand{\Yfirst}{B}
\newcommand{\Ysecond}{yy}
\newcommand\mycommand[1]{%
 \csname #1first\endcsname
 \csname #1second\endcsname
 \hypertarget{#1label}{}%
}
\begin{document}
    \section{Section}
    \label{section1}
    \mycommand{X}
    \hyperlink{Ylabel}{l1Y}
    \newpage
    \section{Another section}
    \label{section2}
    \hyperlink{Xlabel}{l2X}
    \hyperlink{Ylabel}{l2Y}
    \newpage
    \mycommand{Y}
    \hyperlink{Xlabel}{l3X}
    See Section 1 here~\ref{section1}.
    See Section 2 here~\ref{section2}.
\end{document}

A third attempt, with \phantomsection. It also seems to work. This is the better solution.

\documentclass{article}
\usepackage{hyperref}
\newcommand{\Xfirst}{A}
\newcommand{\Xsecond}{xx}
\newcommand{\Yfirst}{B}
\newcommand{\Ysecond}{yy}
\newcommand\mycommand[1]{%
 \csname #1first\endcsname
 \csname #1second\endcsname
 \phantomsection
 \label{#1label}{}%
}
\begin{document}
    \Huge
    \section{Section}
    \label{section1}
    \mycommand{X}
    X\pageref{Xlabel}
    Y\pageref{Ylabel}
    \newpage
    \section{Another section}
    \label{section2}
    X\pageref{Xlabel}
    Y\pageref{Ylabel}
    \newpage
    \mycommand{Y}
    X\pageref{Xlabel}
    Y\pageref{Ylabel}\par
    See Section 1 here~\ref{section1}.\par
    See Section 2 here~\ref{section2}.
\end{document}

Answer 1

You can generate a variable-named macro using the "environment" \csname...\endcsname. For example, you could define:

\newcommand\mycommand[1]{%
 \csname #1first\endcsname
 \csname #1second\endcsname
 \label{#1label}%
}

which will produce exactly what you asked for.

Edit: Your example does display a bug, but not with my code. The same thing happens if you replace the calls to \mycommand with direct \labels (of Xlabel and Ylabel). This is because hyperref itself does not produce correct links with \pageref; this issue is discussed in this comp.text.tex post.

The basic reason for this is that, while \label saves the target reference's information in the .aux file, it does not produce a hypertarget at the place it is executed. The target for \pageref is therefore exactly the same as the target for \ref, namely, the \section (or equation, or whatever) that produced it. If you want to get around this, you must indicate to hyperref that you want the \label to refer not to the last \section, but to the present location. This is done by inserting \phantomsection right before \label. Thus, if this is your problem, you should use the following definition of \mycommand:

% Use this in case you *don't* install hyperref.
\providecommand\phantomsection{}
\newcommand\mycommand[1]{%
 \csname #1first\endcsname
 \csname #1second\endcsname
 \phantomsection
 \label{#1label}%
}

However, this will break uses of \ref, since they will now point to the location of the label rather than the labeled section. I don't think you can have it both ways without hacking \label.