3.4. Address ranges in GNU sed and HHsed
(1) GNU sed 3.02+, ssed, and sed15+ all support address ranges like:
/regex/,+5
which match /regex/ plus the next 5 lines (or EOF, whichever comes
first).
(2) GNU sed v3.02.80 (and above) and ssed support address ranges of:
0,/regex/
as a special case to permit matching /regex/ if it occurs on the
first line. This syntax permits a range expression that matches
every line from the top of the file to the first instance of
/regex/, even if /regex/ is on the first line.
(3) HHsed (sed15) has an exceptional way of implementing
/regex1/,/regex2/
If /RE1/ and /RE2/ both occur on the same line, HHsed will match
that single line. In other words, an address range block can
consist of just one line. HHsed will then look for the next
occurrence of /regex1/ to begin the block again.
Every other version of sed (including sed16) requires 2 lines to
match an address range, and thus /regex1/ and /regex2/ cannot
successfully match just one line. See also the comments at
section 7.9.4, below.
(4) BEGIN~STEP selection: ssed and GNU sed (v2.05 and above) offer
a form of addressing called "BEGIN~STEP selection". This is not a
range address, which selects an inclusive block of consecutive
lines from /start/ to /finish/. But I think it seems to belong here.
Given an expression of the form "M~N", where M and N are integers,
GNU sed and ssed will select every Nth line, beginning at line M.
(With gsed v2.05, M had to be less than N, but this restriction is
no longer necessary). Both M and N may equal 0 ("0~0" selects every
line). These examples illustrate the syntax:
sed '1~3d' file # delete every 3d line, starting with line 1
# deletes lines 1, 4, 7, 10, 13, 16, ...
sed '0~3d' file # deletes lines 3, 6, 9, 12, 15, 18, ...
sed -n '2~5p' file # print every 5th line, starting with line 2
# prints lines 2, 7, 12, 17, 22, 27, ...
(5) Finally, GNU sed v2.05 has a bug in range addressing (see
section 7.5), which was fixed in the higher versions.
