Commands defined with * options

LaTeX commands commonly have « versions » defined with an asterisk tagged onto their name : for example \newcommand and \newcommand* (the former defines a \long version of the command).

The simple-minded way for a user to write such a command involves use of the ifthen package :

\newcommand{\mycommand}[1]{\ifthenelse{\equal{#1}{*}}%
  {\mycommandStar}%
  {\mycommandNoStar{#1}}%
}
\newcommand{\mycommandStar}{starred version}
\newcommand{\mycommandNoStar}[1]{normal version}

This does the trick, for sufficiently simple commands, but it has various tiresome failure modes, and it requires \mycommandnostar to take an argument.

The LaTeX kernel does a lot of this, and has its own command, \@ifstar (which needs « internal command protection », cf.

\makeatletter
\newcommand{\mycommand}{%
             \@ifstar
                  \mycommandStar%
                  \mycommandNoStar%
\makeatother
}
\newcommand{\mycommandStar}{starred version}
\newcommand{\mycommandNoStar}{normal version}

(Note that arguments to \mycommandStar and \mycommandNoStar are independent — either can have their own arguments, unconstrained by the technique we’re using, unlike the trick described above.) The \@ifstar trick is all very well, is fast and efficient, but it requires that the definition be \makeatletter protected.

A pleasing alternative is the suffix package. This elegant piece of code allows you to define variants of your commands :

\newcommand\mycommand{normal version}
\WithSuffix\newcommand\mycommand*{starred version}

The package needs e-LaTeX, but any new enough distribution defines LaTeX as e-LaTeX by default. Command arguments may be specified in the normal way, in both command definitions (after the * in the \WithSuffix version). You can also use the TeX primitive commands, creating a definition like :

\WithSuffix\gdef\mycommand*{starred version}

For those of an adventurous disposition, a further option is to use the xparse package from the l3packages distribution. The package defines a bunch of commands (such as \NewDocumentCommand) which are somewhat analagous to \newcommand and the like, in LaTeX2ε. The big difference is the specification of command arguments; for each argument, you have a set of choices in the command specification. So, to create a *-command (in LaTeX2ε style), one might write :

\NewDocumentCommand \foo { s m } {%
  % #1 is the star indicator
  % #2 is a mandatory argument
  ...
}

The « star indicator » (s) argument appears as #1 and will take values \BooleanTrue (if there was a star) or \BooleanFalse (otherwise); the other (m) argument is a normal TeX-style mandatory argument, and appears as #2.

While xparse provides pleasing command argument specifications, it is part of the LaTeX 3 experimental harness. Simply loading the package to provide \DeclareDocumentCommand « pulls in all of the LaTeX3 kernel (a large bunch of packages) via the expl3 package.

---

Sources

Commands defined with * options