How to pass vertical line

samedi 29 novembre 2014

I have a complex problem for which there is no reasonable MWE.

The idea is to test whether #1 is empty and if it isn't then write vertical line "|" and #1:


\ifx\\#1\\
  % do nothing
 \else
  |#1
\fi

This is not working. I guess symbol "|" has some special meaning for \ifx command (perhaps OR). Is there any way to pass symbol "|"?

TeX - LaTeX