To whom it may concern,

I noticed something odd while fooling around with sed.  If you try to
remove multiple line intervals (by number) from a file, but any interval
specified later in the list is a subset of an interval earlier in the list,
then an additional single line is removed after the specified (larger)
interval.

seq 10 > foo.txt

sed '2,7d;3,6d' foo.txt
1
9
10

Expected output is:

1
8
9
10

Additional tests:

For each additional redundant interval, another line is removed:
sed '2,7d;3,6d;4,5d' foo.txt
1
10

Reversing the order of the intervals produces the expected result!
sed '3,6d;2,7d' foo.txt
1
8
9
10

Specifying the intervals with '-e' produces the same result:
sed -e '2,7d' -e '3,6d' foo.txt
1
9
10

Using different interval syntax has mixed results:
sed -e '/2/,/7/d' -e '/3/,/6/d' foo.txt
1
8
9
10
sed -e '2,7d' -e '/3/,/6/d' foo.txt
1
8
9
10
sed -e '/2/,/7/d' -e '3,6d' foo.txt
1
9
10

Trailing list must be a subset for the additional line to be removed:

sed '2,5d;1,5d'
1
8
9
10
sed '2,5d;2,6d'
1
8
9
10
sed '2,5d;2,5d'
1
9
10

Versions:

Breakage appears to have occurred in the 4.1 release.  See the expected
output for all cases in GNU sed 3.02 and 4.09 (as well as BSD sed (Mac OS X
10.2 Yosemite and /bin/sed on Solaris), but not in 4.15 and 4.21.

This issue and above information has been discussed on stack overflow:
stackoverflow.com/questions/28595574/deleting-lines-of-a-file-with-sed-unexpected-behaviour

Cheers,
Ethan