How to replace text in a file using sed and a regular expression?

Question

linux

You need to replace the text in the file according to the regular expression. In PHP it works without problems.
The task is this:
Find the text by the expression
#\[0-9]+\<\/maxplayers\>#
And replace the numbers in it.
For example
55
Replace with
128
I write like this:
sed -i 's#\[0-9]+\<\/maxplayers\>#55#g' /path/to/file
Judging by the file update time, it writes something . But no change...

Answer 1

sed -i '/<\/maxplayers>/{s/55/128/g}' /path/to/file

Answer 2

test on a single line file.

Answer 3

# change to /