Using sed with regex to replace text on OSX and Linux

I am trying to replace some strings inside a file with sed using Regular Expressions. To complicate the matter, this is being done inside a Makefile script that needs to work on both osx and linux.

Specifically, within file.tex I want to replace

subimport{chapters/}{xxx}

with

subimport{chapters/}{xxx-yyy}

(xxx and yyy are just example text.)

Note, xxx could contain any letters, numbers, and _ (underscore) but really the regex can simply match anything inside the brackets. Sometimes there is some whitespace at the beginning of the line before subimport....

The design of the string being searched for requires a lot of escaping (when searched for with regex) and I am guessing somewhere therein lies my error.

Here’s what I’ve tried so far:

sed -i'.bak' -e 's/\subimport{chapters/}{xxx}/\subimport{chapters/}{xxx-yyy}/g' file.tex
# the -i'.bak' is required so SED works on OSX and Linux
rm -f file.tex.bak # because of this, we have to delete the .bak files after

This results in an error of RE error: invalid repetition count(s) when I build my Makefile that contains this script.

I thought part of my problem was that the -E option for sed was not available in the osx version of sed. It turns out, when using the -E option, fewer things should be escaped (see comments on my question).

Answer

Here’s is the version that ended up working for me.

sed -i.bak -E 's#^([[:blank:]]*\subimport{chapters/}{[[:alnum:]_]+)}$#1-yyy}#' file.tex
rm -f file.tex.bak

Much thanks go to @heemayl. Their answer is the better written one, it simply required some tweaking to get a version that worked for me.