# emacs Regular Expressions (regexp) Examples

Posted by rolf on Tuesday, 4 August 2015

### ||Symbols Text a^2|| -> \norm{Symbols Text a^2}

in Latex change I defined my own norm environment, using the \usepackage{amsmath} environment, by

\newcommand{\norm}[1]{\left\Vert#1\right\Vert}

Now I wanted to replace every pair || . || with \norm{.}, e.g.

||a^2 - b^2||^2

to

\norm{a^2 - b^2}^2

###### REGEXP

M-x query-replace-regexp

||\(.*?\)||

with

\\norm{\1}

The .* matches everything in a greedy way, that means a expression like

|| test || + || test2||

would be matched and replaced to

\norm{test || + ||test2}

What we want is a non-greedy regexp, hence the .*?, this replaces above to

\norm{ test} + \norm{test2}

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