newly learned sed tech tips

1. flow control

   sed support simple flow control

   use the keyword "b" to jump to a label,and beware of where you put the label.

2. the use of N

   when sed see a N, it reads the next line into the pattern buffer.

   then you can do substitute,delete with the pattern buffer.

 

the following code combines 2 lines into one as long as the first one ends with ";"

/;$/{
N;
s/;\n/;/
}

3. the usage of NF

   you have to add a '$' sign ahead of NF under HP-UX,otherwise you will never get what you want.