Using sed to delete a whole line if it contains only specific number

Question

I have a txt file

123
456
789
456
123456

I want to delete specific characters from the file i.e (123). I tried with

$ sed -i '/123/d' dummy.sh
$ vi dumm.txt
456
789
456

In the below command when I run both the words (123 and 123456) are getting deleted but I need to delete only 123 from the file

$ sed -i 's/123//g' dummy.sh
$ vi dumm.txt
456
789
456
456

when I run the below command the 123 is getting replaced with null.

Can anyone say how to delete a whole line if it contains only specific number?

Answer 1

It is unclear if you are trying to delete whole line with 123 or replace it with empty line. Anyhow, just add anchors of beginning ^ and end $ of line to your pattern:

sed -i '/^123$/d' dummy.sh      #delete whole line
sed -i 's/^123$//' dummy.sh     #replace with empty line