Optional argument for newcommand?

Question

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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?

Note that [0] here would create a command with no arguments at all: you need [1][] to have one optional argument. — Joseph Wright, Jun 05 '12 at 11:06

score 100 · Accepted Answer · answered Jun 05 '12 at 11:05

100

\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

answered Jun 05 '12 at 11:05

Tom Bombadil

40,123

58

Slightly better: \ifthenelse{\isempty{#1}} (the \isempty test is provided by xifthen. – egreg Jun 05 '12 at 11:11
7

Oh, I didn't know it existed. You live and learn! – Tom Bombadil Jun 05 '12 at 11:14
1

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 03 '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
@TomBombadil why does it stop working as an optional argument if you want to use {}? It is just because the {} works as a grouping here, and not as the "parenthesis" for a command or something? Essentially: with the code you wrote above, why does it fail to work as expected when I write \test{testarg}? – Marses Jul 14 '20 at 16:13
Additionally, when I make the argument non-optional, why does \test[testarg] not work as expected (it seems not actually pass any argument). – Marses Jul 16 '20 at 11:43
1

I am trying to define a command as such: \newcommand{\gesetze}[2]{http://www.gesetze-im-internet.de/#1/\ifthenelse{\equal{#2}{}}{}{__#2.html}}
The idea is that, if an optional second argument is given, it appends __#2.html to the url, and if not, it ends after #1/. However, this gives an error.
– Marie. P. Aug 01 '20 at 22:24

Optional argument for newcommand?

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