Using sed to replace a pattern by symbol

Question

How do I replace a pattern by looking at sentence symbol by using sed?
Input

this-
-this-

Results I want

start
middle

My code

sed 's/[a-zA-Z]-/start/g'
sed 's/-[a-zA-Z]-/middle/g'

Results I get

abastart

Am I doing something wrong?

Answer 1

This should do:

sed -r 's/^[a-zA-Z]+-/start/;s/^-[a-zA-Z]+-/middle/' file
start
middle

• -r or -E for extended regex
• + to tell its 1 or more character
• ^ to tell to start from beginning of line
• ; to have more than one sed block in one line
• You can add $ to make sure whole line is matched s/^[a-zA-Z]+-$/start/