tests: more automated quote adjustment

Relax initial regexp to match more instances, but add a
filter to avoid some invalid conversions.  Run this:

git grep -l "\`[^']*'" tests | xargs perl -pi -e '$q=q"'\''";' \
  -e '$q="$q\\$q$q"; /(= ?\`|\`expr|\`echo|\Q$q\E)/ and next;' \
  -e ' s/\`([^'\''"]*?'\'')/'\''$1/g'
The last disjunct in the above (...) filter is to exempt
any line that contains this string: '\''
With quoting like that, converting a ` to ' is likely to cause trouble,
so we'll handle those manually.  Here are three examples where
the exemption is required:

  *': `link-to-dir/'\'': hard link not allowed for directory'*) ;;
  printf 'creating file `%s'\''\n' $f
  'mv: inter-device move failed: `%s'\'' to `%s'\'';'\

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/misc/stdbuf b/tests/misc/stdbuf
index 99bb24300..bf4edc179 100755
--- a/tests/misc/stdbuf
+++ b/tests/misc/stdbuf
@@ -96,7 +96,7 @@ retry_delay_ stdbuf_unbuffer .1 6 || fail=1
 #  One could remove the need for dd (used to close the fifo to get uniq to quit
 #  early), if head -n1 read stdin char by char. Note uniq | head -c2 doesn't
 #  suffice due to the buffering implicit in the pipe.  sed currently does read
-#  stdin char by char, so we can test with 'sed 1q`.  However I'm wary about
+#  stdin char by char, so we can test with 'sed 1q'.  However I'm wary about
 #  adding this dependency on a program outside of coreutils.
     # printf '2\n' > exp
     # printf '1\n2\n' | (stdbuf -i0 sed 1q >/dev/null; cat) > out