bug#25587: In -i mode, shouldn't sed continue processing the command line if it can't access some files?

[Zack Weinberg]

Consider

$ mkdir test
$ cd test
$ printf 'foo\nbar\n' > a
$ mkdir b
$ printf 'foo\nbar\n' > c
$ sed -i '$d' *
sed: couldn't edit b: not a regular file
$ ls -l
-rw-r--r-- 1 zack zack    4 Jan 31 10:06 a
drwxr-xr-x 2 zack zack 4096 Jan 31 10:06 b
-rw-r--r-- 1 zack zack    8 Jan 31 10:06 c

I find this behavior surprising.  In -i mode, I think sed should go on
to process 'c' even though it failed to process 'b'.

$ sed --version | sed 1q
sed (GNU sed) 4.3

zw