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Possible Duplicate:
Different command definitions with and without optional argument

I would like to define a macro which takes an optional argument, and behaves in different ways depending on if the optional argument is given or not. As a very simple example, I would like to define a new macro

\newcommand{\example}[0][]{macro definition}

which outputs

optional argument was omitted

if the optional argument was omitted, and

optional argument was given

if the optional argument was given. How can I achieve this?

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marked as duplicate by Loop Space, David Carlisle, egreg, lockstep, yo' Jun 5 '12 at 11:11

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  • Note that [0] here would create a command with no arguments at all: you need [1][] to have one optional argument. – Joseph Wright♦ Jun 5 '12 at 11:06
76
\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{xifthen}

\newcommand{\test}[1][]{%
\ifthenelse{\equal{#1}{}}{omitted}{given}%
}

\begin{document}

The optional argument was \test[].

The optional argument was \test[shubidu].

\end{document}

Which results in

enter image description here

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  • 44
    Slightly better: \ifthenelse{\isempty{#1}} (the \isempty test is provided by xifthen. – egreg Jun 5 '12 at 11:11
  • 5
    Oh, I didn't know it existed. You live and learn! – Tom Bombadil Jun 5 '12 at 11:14
  • Also, it seems \ifx can be used: \newcommand{\test}[1][]{ \def\tst{#1} \ifx\tst\empty \typeout{optional argument was omitted} \else \typeout{optional argument was given: '#1'} \fi } – sdaau Jun 3 '15 at 17:03
  • @TomBombadil Is there a way to make \test accept its argumets with {} rather than with []? – yohbs Oct 27 '15 at 12:45
  • 6
    @yohbs: Yes, but then it would not be an optional argument anymore: \newcommand{\test}[1]{\ifthenelse{\isempty{#1}{}}{omitted}{given}} – Tom Bombadil Oct 27 '15 at 12:49

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