bin/188535: ed/red - incorrectly sets current address upon removing last line

[Volodymyr Kostyrko]

>Number:         188535
>Category:       bin
>Synopsis:       ed/red - incorrectly sets current address upon removing last line
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sat Apr 12 21:40:02 UTC 2014
>Closed-Date:
>Last-Modified:
>Originator:     Volodymyr Kostyrko
>Release:        ^/stable/10
>Organization:
none
>Environment:
FreeBSD kohrah.xim.bz 10.0-RELEASE-p1 FreeBSD 10.0-RELEASE-p1 #1 r264316M: Thu Apr 10 16:38:26 EEST 2014     root at kohrah.xim.bz:/usr/obj/usr/src/sys/MINIMAL  amd64
>Description:
Let's have some file:

  echo xxx > some_file
  echo yyy >> some_file

Now let's try to edit it with ed, lines starting from '>' are manual input:

> ed some_file
  8
> H
> =
  2
> g/yyy/d
> =
  2
> g/xxx/d
> =
  0
> g/zzz/d
  ?
  invalid address

When last line is removed from file current address is changed from 1 to 0 making all subsequent range addressing to fail. This violates the man page:

    Since the g (global) command masks any errors from failed searches and
    substitutions, it can be used to perform conditional operations in
    scripts; --

What I mean is that actually using g (global) is not fully safe. Imagine I have a number of key fingerprints and I want to create a simple script to remove them from 'known_hosts' throughout all of my machines. There are a lot of fingerprints but each known_hosts file can contain only a few of them thus script may fail when file is running out of lines.
>How-To-Repeat:

>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: