# How can I throw a custom error from \newcommand

I'd like to write a command that checks the given arguments and throws an error if they are not in a range.

I'm imagining this would look something like this:

\usepackage{xifthen}

\newcommand{\wb}[2][]{\ifthenelse{{#2} > 0 \AND {#2} < 7}
{\includegraphics[{#1}]{wong-baker/{#2}.eps}}}
{%throw error here}
}


How can I check parameters in newcommand?

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## 1 Answer

\PackageError{mypackage}{dont do that}{extra help}


see section 4.9 of texdoc clsguide

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Does this also work for a quick command which is not inside any package? –  ipavlic Jun 9 '14 at 12:19
@ipavlic yes you can put anything you like in the mypackage argument it doesn't have to be really the name of a package. –  David Carlisle Jun 9 '14 at 12:20