I will start with the original command rather than building from scratch. Building from scratch is an excellent approach in this case, still there is an educational value in understanding the original command and steps you can take to adjust the command to your needs.
The core of the original command:
sed -e 's/\(+\).*\(@\)/\1\2/'
The expression is in a form
s/pattern/replacement/, which means "search for
pattern and replace it with
/ is the separator here.
\(+\).*\(@\). Its matching function would be the same if it was
+.*@ (enclosing something in
\( \) is relevant in the context of
replacement, we will get to it). A pattern of
+.*@ means "literal
+ followed by (almost) any character (
.) repeated zero or more times (
*), followed by literal
+ matches the first possible
* is greedy so this match spans from the first
+ to the last
@. It may not matter in your specific case, still sometimes it's very important.
Your replacement is
\1\2. It means "whatever was matched by the 1st
\( \) followed by whatever was matched by the 2nd
\( \)". Your first
\( \) is in fact
\(+\), it matches
+ you want to get rid of.
To make it clear: the reason these
\( \) groups appear in the pattern (so the pattern is not just
+.*@) is they define fragments referred to as
So if you don't want
+ to be printed, the minimal change to your original command will be to omit
\1, because this is the exact part that prints
+ in your case.
sed -e 's/\(+\).*\(@\)/\2/'
But then you don't need
\( \) around
+ in the pattern, therefore you can simplify:
sed -e 's/+.*\(@\)/\1/'
\(@\) is now the 1st
\( \) group. Also, since it can only match
@, you can use the literal
@ instead of
sed -e 's/+.*\(@\)/@/'
But now you don't need
\( \) at all. The command becomes:
sed -e 's/+.*@/@/'
Then you recall
* is greedy so
.* may include (extra)
@. Let's suppose you don't want this. You need to turn
. into something that matches anything but
sed -e 's/+[^@+]*@/@/'
This is exactly what this other answer gave you. Somewhat experienced
sed user would build this solution from scratch. As you can see it's possible to reduce your original command, step by step in a logical manner, and get to the same solution.