Given a file like this:
$ cat file
hello/how/are/you
i am fine
You can use /pattern/ to match specific lines:
$ sed -n '/hello/p' file
hello/how/are/you
If the pattern contains slashes itself, you can use another delimiter using \cBREc:
$ sed -n '\#hello/how#p' file
hello/how/are/you
$...
