#!/bin/bash
sed '{
#remove empty line
s/^M$//
s/.$//
/^$/d
s/^!/#&/
:a
s/^#\(.*\)/\1/
ta
/^\[.*\]/ {N; s/\n/ /}
}' input.txt
#!/bin/bash
sed '{
#remove empty line
s/^M$//
s/.$//
/^$/d
s/^!/#&/
:a
s/^#\(.*\)/\1/
ta
/^\[.*\]/ {N; s/\n/ /}
}' input.txt