Switch a TeX \macro and a script on a region of text

Question

How can I search and replace in a region of a (TeX)buffer all occurences of \macro{foo}_{bar} to \macro{foo_{bar}}, foo and bar not being "constants" ?

Answer 1

Use regexp replacement (M-x replace-regexp or C-M-%) to replace a pattern with holes.

Assuming that foo and bar do not themselves contain braces or line breaks, replace \\macro{\(.*?\)}_{\(.*?\)} by \\macro{\1_{\2}}. Explanations (see the manual for more details):

• \ is a special character, so you need to write \\ to match one backslash.
• \(…\) is a group: Emacs will remember what the group matched.
• .*? matches any sequence of characters except a line break. It stops as early as possible (whereas .* would stop as late as possible, and could thus end up matching all of \macro{foo}_{bar} and more \stuff{baz}).
• In the replacement, \1 and \2 are replaced by what the corresponding group matched.