In my text file there are many lines whose contents are almost the same. Here are some of them.

So, right now I’m using:

cat text | sed "///s/^/- /g;s// /n- /g"

Input file:

1
00:00:00,000 --> 00:00:00,000
You are older.

2
00:00:00,000 --> 00:00:00,000
By length of a sunset.
/ Is older.

3
00:00:00,000 --> 00:00:00,000
Soona.

Expected output:

1
00:00:00,000 --> 00:00:00,000
You are older.

2
00:00:00,000 --> 00:00:00,000
- By length of a sunset.
- Is older.

3
00:00:00,000 --> 00:00:00,000
Soona.