[RFC] t: allow use of "sed -E"

[Junio C Hamano <gitster@pobox.com>]

Since early 2019 with e62e225f (test-lint: only use only sed [-n]
[-e command] [-f command_file], 2019-01-20), we have been trying to
limit the options of "sed" we use in our tests to "-e <pattern>",
"-n", and "-f <file>".

Before the commit, we were trying to reject only "-i" (which is one
of the really-not-portable options), but the commit explicitly
wanted to reject use of "-E" (use ERE instead of BRE).  The commit
cites the then-current POSIX.1 (Issue 7, 2018 edition) to show that
"even recent POSIX does not have it!", but the latest edition (Issue
8) documents "-E" as an option to use ERE.

But that was 7 years ago, and that is a long time for many things to
happen.

Besides, we have been using "sed -E" without the check in question
triggering in one of the scripts since 2022, with 461fec41 (bisect
run: keep some of the post-v2.30.0 output, 2022-11-10).  It was
hidden because the 'E' was squished with another single letter
option.

t/t6030-bisect-porcelain.sh:	sed -En 's/.*(bisect...

This escaped the rather simple pattern used in the checker

    /\bsed\s+-[^efn]\s+/ and err 'sed option not portable...';

because -E did not appear as a singleton.

Let's change the rule to allow the "-E" option, which nobody has
complained against for the past 3 years.  We rewrite our first use
of the "-E" option so that it is caught by the old rule, primarily
because we do not want to teach our mischievous developers how to
smuggle in an unwated option undetected by the test lint.  And at
the same time, loosen the pattern to allow "-E" the same way we
allow "-n" and friends.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 t/check-non-portable-shell.pl | 2 +-
 t/t6030-bisect-porcelain.sh   | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git c/t/check-non-portable-shell.pl w/t/check-non-portable-shell.pl
index 6ee7700eb4..dd8af6d08f 100755
--- c/t/check-non-portable-shell.pl
+++ w/t/check-non-portable-shell.pl
@@ -36,7 +36,7 @@ sub err {
 
 	$_ = $line;
 	/\bcp\s+-a/ and err 'cp -a is not portable';
-	/\bsed\s+-[^efn]\s+/ and err 'sed option not portable (use only -n, -e, -f)';
+	/\bsed\s+-[^Eefn]\s+/ and err 'sed option not portable (use only -n, -e, -f)';
 	/\becho\s+-[neE]/ and err 'echo with option is not portable (use printf)';
 	/^\s*declare\s+/ and err 'arrays/declare not portable';
 	/^\s*[^#]\s*which\s/ and err 'which is not portable (use type)';
diff --git c/t/t6030-bisect-porcelain.sh w/t/t6030-bisect-porcelain.sh
index cdc0270640..1ba9ca219e 100755
--- c/t/t6030-bisect-porcelain.sh
+++ w/t/t6030-bisect-porcelain.sh
@@ -402,7 +402,7 @@ test_expect_success 'git bisect run: negative exit code' "
 	git bisect good $HASH1 &&
 	git bisect bad $HASH4 &&
 	! git bisect run ./fail.sh 2>err &&
-	sed -En 's/.*(bisect.*code) (-?[0-9]+) (from.*)/\1 -1 \3/p' err >actual &&
+	sed -E -n 's/.*(bisect.*code) (-?[0-9]+) (from.*)/\1 -1 \3/p' err >actual &&
 	test_cmp expect actual
 "