How to replace single line in the text file with bash?

Question

I would like to replace one (first line) in app.yaml file I have with bash. The file looks like below:

application: my-appid
version: 1
...

my-appid there should be replaced with my-appid2.

I tried to use

sed -i.bak -e "s/application: \.*/application: \ 2/" app.yaml

but in result I get application: 2my-appid.

How should I fix it? (my-appid shouldn't be hardcoded)

Answer 1

sed -i.bak -e 's/application: .*/&2/' app.yaml

& in the replacement gets replaced with everything that matched the regexp.

Answer 2

sed -i.bak -e '1s/ .*/ my-appid2/' app.yaml

On line 1, replace a space followed by anything, with a space followed by your new app name.