How to customize a newcommand?

Question

I want to customize a command \myvec{arg}.

If the argument is a single character, then \bm{arg}

else then \vv{arg}

It would have been helpful to have shown which packages \bm and \vv were coming from by giving a minimal working example. — Alan Munn, Apr 16 '17 at 00:27
Since you have some responses below that seem to answer your question, please consider marking one of them as ‘Accepted’ by clicking on the tickmark below their vote count (see How do you accept an answer?). This shows which answer helped you most, and it assigns reputation points to the author of the answer (and to you!). It's part of this site's idea to identify good questions and answers through upvotes and acceptance of answers. — samcarter_is_at_topanswers.xyz, May 19 '17 at 10:42

score 10 · Answer 1 · answered Apr 16 '17 at 00:18

Adapting code from:

How to find out if a math list consists of a single character?

the following seems to work:

\documentclass{article}
% This code by Hendrik Vogt https://tex.stackexchange.com/a/70562/2693
\newcommand*\ifsingle[3]{%
  \setbox0\hbox{$\mathaccent"0362{#1}^H$}%
  \setbox2\hbox{$\mathaccent"0362{\kern0pt#1}^H$}%
  \ifdim\ht0=\ht2 #3\else #2\fi
  }
\usepackage{bm}
\def\vv{} % define as needed
\newcommand*\myvec[1]{\ifsingle{#1}{\bm{#1}}{\vv{#1}}}
\begin{document}
$\myvec{a}$
$\myvec{aa}$
$\myvec{\alpha}$
$\myvec{\alpha\beta}$
\end{document}

How to customize a newcommand?

1 Answers1