Write command so that commas appear properly

Question

Possible Duplicate:
\newcommand and spacing

I want to write a command as a shortcut to insert text.

\newcommand{\bl}{$blah blah$}

When I write the command like this, "blah blah" runs into the next word. If I put a space after the second "$", then when I have

\bl,

I get

blah blah ,

with a space before the comma. What's the proper way of doing this.

Answer 1

Use the xspace package,

\documentclass{article}
\usepackage{xspace}
\newcommand{\bl}{$blah blah$\xspace}
\begin{document}
\bl, \bl this is fine.
\end{document}