Using sed command to delete lines in file in Debian Linux

Question

I want to ask you if you know how to delete lines in single file using sed command on Linux.

For example I have got file:

       something
       something-
       somethingelse

And I want create sed command to delete all lines where line contains "something", but also I dont want delete line where is something-. Where is specific char like "-". Thank you for advice.

I tried to make something like sed -i "/something/d".

Answer 1

sed -e '/something[^-]/d' -e '/something$/d' -i "$file"

even shorter, proposed by Philippos:

sed -i '/something\([^-].*\)*$/d' "$file"

Answer 2

Assuming it is more important to keep lines that contain something- than it is to delete lines that contain something:

sed '/something/ { /something-/!d; }' file

This finds all lines containing the string something, and deletes all of those lines unless they also contain something-.

Testing:

$ cat file
something something blah blah
something something- blah blah
somethingelse
something
something-

$ sed '/something/ { /something-/!d; }' file
something something- blah blah
something-