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

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?

-
–  Peter Grill Aug 11 '11 at 9:41
@xport Check my code on about line 2 (command factory) at tex.stackexchange.com/questions/13333/… –  Yiannis Lazarides Aug 28 '11 at 17:56

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).

-
Unbelievable. You beat me to it by 49 seconds! –  Ian Thompson Aug 11 '11 at 8:59
I guess that the fact you're using \newcommand (with the benefits that that brings) is why you didn't mention \@namedef. –  Loop Space Aug 11 '11 at 9:01
@Andrew: Yes, also \@namedef requires \makeatletter ... \makeatother, which is a little annoying. However, for packaged code without optional arguments \@namedef{#1}{My name is #1} would also be an easy option. –  Martin Scharrer Aug 11 '11 at 9:05
@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. –  Martin Scharrer Aug 11 '11 at 9:55
@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 '11 at 10:22
\documentclass{article}

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

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

-

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

-
With etoolbox, you can use \csdef, \csgdef then. –  Leo Liu Aug 11 '11 at 10:28
@Leo but then you don't have the protection from overwriting definitions that \newcommand gives you... –  Seamus Aug 11 '11 at 11:17
+1 I might need this technique in the future. Thanks. –  xport Aug 11 '11 at 11:50
With the help of a simple shell script, you can use this to get a list of all the filenames of images in a directory, and create a command that includes each one... (That's what I used it for.) –  Seamus Aug 11 '11 at 12:26