Frequently Asked Question List for TeX

# Commands defined with * options


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 LaTeX2e. 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 LaTeX2e 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.

FAQ ID: Q-cmdstar
Tags: latexmacros