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I want to define a macro \create that accept a single mandatory argument from which another new macro is created and named.

The following code snippet may speak clearer what I want to achieve. But the following code cannot be compiled because it is wrong. :-)

\documentclass{article}

\newcommand\create[1]{%
\newcommand\#1{My name is #1}}

\begin{document}
\create{test}
\test
\end{document}

How to define a macro to create a new macro with a name passed as its argument?

2

4 Answers 4

32

Use \csname #1\endcsname which must be expanded before \newcommand using \expandafter:

\newcommand\create[1]{%
\expandafter\newcommand\csname #1\endcsname{My name is #1}}
% usage: \create{foobar}

If you want to pass the macro as control sequence instead, i.e. \foobar instead of foobar then you need to turn it into a string and remove the backslash:

\makeatletter
\newcommand\create[1]{%
\expandafter\newcommand\csname\expandafter\@gobble\string#1\endcsname{My name is #1}}
\makeatother
% usage: \create{\foobar}

There is also the \@namedef macro which is defined as \expandafter\def\csname #1\endcsname, so you can use it as:

\newcommand\create[1]{\@namedef{My name is #1}}

The etoolbox package also provides a basically identical, but robust macro called \csdef. For both you can provide a parameter text, e.g. for arguments direct after the name argument: \csdef{name}#1#2{some code with two arguments #1 and #2} (the # have to be doubled inside another macro).

4
  • 1
    @xport: In this case you must define the macro globally, i.e. either use \global\@namdef{#1}{<content>} or, if you need \newcommand, \global\expandafter\let\csname #1\expandafter\endcsname\csname #1\endcsname. Aug 11, 2011 at 9:55
  • 1
    @xport: Yes, using \gdef` instead of \newcommand will do it as well. Aug 11, 2011 at 10:15
  • 2
    @xport: You didn't provide the real example to explain why grouping is necessary. There are many tricks to define a macro in group, e.g. {\def\x{\def\foo{bar}}\expandafter}\x. But you should firstly persuade us (and yourself) to believe that it is necessary to use these tricks.
    – Leo Liu
    Aug 11, 2011 at 10:22
  • @Leo: If you are interested in avoiding grouping, see my answer. I just applied what I learnt from this question. Aug 11, 2011 at 11:41
6
\documentclass{article}

\newcommand\create[1]{%                                                         
\expandafter\def\csname #1\endcsname{My name is #1}}

\begin{document}
\create{test}
\test
\end{document}
5

If you're going to be doing lots of this sort of thing, you can create a bunch of macros in one go from a comma separated list with some etoolbox magic:

\usepackage{etoolbox}
\newcommand\create[1]{%
\expandafter\newcommand\csname #1\endcsname{My name is #1}}
\newcommand\createlist{%
\let\do\create
\docsvlist
}

The argument of \createlist should be a list like: \createlist{foo,Foo,magic,jabberwocky} and it will create \foo,\Foo,\magic,\jabberwocky

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  • 2
    With etoolbox, you can use \csdef, \csgdef then.
    – Leo Liu
    Aug 11, 2011 at 10:28
  • @Leo but then you don't have the protection from overwriting definitions that \newcommand gives you...
    – Seamus
    Aug 11, 2011 at 11:17
1

If you want to pass the macro name as a macro name:

\documentclass{article}

\newcommand{\create}[1]% #1 = macro name
{\bgroup
  \def\foo{Hello World!}% local definition
  \global\let#1=\foo
\egroup}

\begin{document}
\create{\mymacro}%
\mymacro
\end{document}
2
  • What's the difference between this and \newcommand\create[1]{\def#1{Hello World!}}? Sorry, I don't know much about tex subtleties.
    – coldfix
    Sep 20, 2017 at 21:34
  • @coldfix - I knew \let would work. I wasn't sure about \def, especially if the macro itself has arguments: Sep 21, 2017 at 3:30

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