I tried the following:
# echo "12MB" | sed -e 's/[bm]\*//i'
12MB
# echo "12MB" | sed -e 's/[bm]\+//i'
12
I was expecting both to produce the same output (greedy match), but the one with the star does not. I tried also with gsed, but it was the same result.
When I tried using -E # for extended re neither of the two forms works.
An ubuntu docker container also behaves the same way.
Can someone help me understand why is that?
First, in sed "basic" regexp patterns * is for repetition, \* is a literal asterisk. So your example would be
# echo "12MB" | sed -e 's/[bm]*//i'
12MB
... which still doesn't produce your expected output.
The reason becomes apparent when you use a visible replacement:
# echo "12MB" | sed -e 's/[bm]*/!!!/i'
!!!12MB
The pattern matches right at the start of the string, for a repetition count of zero. After one match, replacement stops.
So you really want one or more repetitions, like in your working example.