Welcome to the UK List of
TeX Frequently Asked Questions
on the Web

Searching

The index of Frequently Asked Questions about TeX is searchable.

Please enter your keyword here:   then press here: ,    or:
Google

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 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.

ifthen.sty
Part of the LaTeX distribution
suffix.sty
Distributed as part of macros/latex/contrib/bigfoot (or browse the directory); catalogue entry
xparse.sty
Distributed as part of macros/latex/contrib/l3packages (or browse the directory); catalogue entry
expl3.sty
Distributed as part of macros/latex/contrib/l3kernel (or browse the directory); catalogue entry

This answer last edited: 2014-04-04


Go to previous question, or next question

Go to FAQ home.

URL for this question: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=cmdstar

Comments, suggestions, or error reports? - see “how to improve the FAQ”.

This is FAQ version 3.28, released on 2014-06-10.