tests: convert nearly all `...` expressions to $(...)

Exempt init.sh because it runs before we're assured to have a
shell that groks $(...).  Exempt *.mk because "$" would have to
be doubled, and besides, any `...` expression in a .mk file is
almost certainly evaluated before init.sh is run.  Finally, also
exempt the perl-based tests, because perl's `...` cannot be
converted to $(...).  Do that by running this command:

git grep -l '`.*`' tests \
  | grep -Ev 'init\.sh|\.mk$' | xargs grep -Lw perl \
  | xargs perl -pi -e 's/`(.*?)`/\$($1)/g'

One minor fix-up change was required after that, due to how
quoting differs:
diff --git a/tests/chmod/equals b/tests/chmod/equals
-    expected_perms=$(eval 'echo \$expected_'$dest)
+    expected_perms=$(eval 'echo $expected_'$dest)

Another was to make these required quoting adjustments:
diff --git a/tests/misc/stty b/tests/misc/stty
...
-  rev=$(eval echo "\\\$REV_$opt")
+  rev=$(eval echo "\$REV_$opt")
...
-      rev1=$(eval echo "\\\$REV_$opt1")
-      rev2=$(eval echo "\\\$REV_$opt2")
+      rev1=$(eval echo "\$REV_$opt1")
+      rev2=$(eval echo "\$REV_$opt2")

Also, transform two files that were needlessly excluded above:
(both use perl, but are mostly bourne shell)

  perl -pi -e 's/`(.*?)`/\$($1)/g' \
    tests/du/long-from-unreadable tests/init.cfg

1 files changed, 24 insertions, 24 deletions

diff --git a/tests/chgrp/basic b/tests/chgrp/basic
index 9c384ba38..8ce2f2ddc 100755
--- a/tests/chgrp/basic
+++ b/tests/chgrp/basic
@@ -33,53 +33,53 @@ chgrp -R $g1 d || fail=1
 
 d_files='d d/f3'
 
-chgrp $g1 f || fail=1  ; test `stat --p=%g f` = $g1 || fail=1
-chgrp $g2 f || fail=1  ; test `stat --p=%g f` = $g2 || fail=1
-chgrp $g2 f || fail=1  ; test `stat --p=%g f` = $g2 || fail=1
-chgrp '' f  || fail=1  ; test `stat --p=%g f` = $g2 || fail=1
-chgrp $g1 f || fail=1  ; test `stat --p=%g f` = $g1 || fail=1
-chgrp $g1 f || fail=1  ; test `stat --p=%g f` = $g1 || fail=1
-chgrp --reference=f2 f ; test `stat --p=%g f` = $g2 || fail=1
-
-chgrp -R $g2 d ||fail=1; test `stat --p=%g: $d_files` = "$g2:$g2:" || fail=1
-chgrp -R $g1 d ||fail=1; test `stat --p=%g: $d_files` = "$g1:$g1:" || fail=1
-chgrp -R $g2 d ||fail=1; test `stat --p=%g: $d_files` = "$g2:$g2:" || fail=1
-chgrp -R $g1 d ||fail=1; test `stat --p=%g: $d_files` = "$g1:$g1:" || fail=1
-chgrp $g2 d    ||fail=1; test `stat --p=%g: $d_files` = "$g2:$g1:" || fail=1
+chgrp $g1 f || fail=1  ; test $(stat --p=%g f) = $g1 || fail=1
+chgrp $g2 f || fail=1  ; test $(stat --p=%g f) = $g2 || fail=1
+chgrp $g2 f || fail=1  ; test $(stat --p=%g f) = $g2 || fail=1
+chgrp '' f  || fail=1  ; test $(stat --p=%g f) = $g2 || fail=1
+chgrp $g1 f || fail=1  ; test $(stat --p=%g f) = $g1 || fail=1
+chgrp $g1 f || fail=1  ; test $(stat --p=%g f) = $g1 || fail=1
+chgrp --reference=f2 f ; test $(stat --p=%g f) = $g2 || fail=1
+
+chgrp -R $g2 d ||fail=1; test $(stat --p=%g: $d_files) = "$g2:$g2:" || fail=1
+chgrp -R $g1 d ||fail=1; test $(stat --p=%g: $d_files) = "$g1:$g1:" || fail=1
+chgrp -R $g2 d ||fail=1; test $(stat --p=%g: $d_files) = "$g2:$g2:" || fail=1
+chgrp -R $g1 d ||fail=1; test $(stat --p=%g: $d_files) = "$g1:$g1:" || fail=1
+chgrp $g2 d    ||fail=1; test $(stat --p=%g: $d_files) = "$g2:$g1:" || fail=1
 
 rm -f f
 touch f
 ln -s f symlink
 chgrp $g1 f
-test `stat --printf=%g f` = $g1 || fail=1
+test $(stat --printf=%g f) = $g1 || fail=1
 
 # This should not change the group of f.
 chgrp -h $g2 symlink
-test `stat --printf=%g f` = $g1 || fail=1
+test $(stat --printf=%g f) = $g1 || fail=1
 
 # Don't fail if chgrp failed to set the group of a symlink.
 # Some systems don't support that.
-test `stat --printf=%g symlink` = $g2 ||
+test $(stat --printf=%g symlink) = $g2 ||
   echo 'info: failed to set group of symlink' 1>&2
 
-chown --from=:$g1 :$g2 f; test `stat --printf=%g f` = $g2 || fail=1
+chown --from=:$g1 :$g2 f; test $(stat --printf=%g f) = $g2 || fail=1
 
 # This *should* change the group of f.
 # Though note that the diagnostic is misleading in that
 # it says the 'group of 'symlink'' has been changed.
-chgrp $g1 symlink; test `stat --printf=%g f` = $g1 || fail=1
-chown --from=:$g1 :$g2 f; test `stat --printf=%g f` = $g2 || fail=1
+chgrp $g1 symlink; test $(stat --printf=%g f) = $g1 || fail=1
+chown --from=:$g1 :$g2 f; test $(stat --printf=%g f) = $g2 || fail=1
 
 # If -R is specified without -H or L, -h is assumed.
-chgrp -h $g1 f symlink; test `stat --printf=%g symlink` = $g1 || fail=1
+chgrp -h $g1 f symlink; test $(stat --printf=%g symlink) = $g1 || fail=1
 chgrp -R $g2 symlink
-chown --from=:$g1 :$g2 f; test `stat --printf=%g f` = $g2 || fail=1
+chown --from=:$g1 :$g2 f; test $(stat --printf=%g f) = $g2 || fail=1
 
 # Make sure we can change the group of inaccessible files.
 chmod a-r f
-chown --from=:$g2 :$g1 f; test `stat --printf=%g f` = $g1 || fail=1
+chown --from=:$g2 :$g1 f; test $(stat --printf=%g f) = $g1 || fail=1
 chmod 0 f
-chown --from=:$g1 :$g2 f; test `stat --printf=%g f` = $g2 || fail=1
+chown --from=:$g1 :$g2 f; test $(stat --printf=%g f) = $g2 || fail=1
 
 # chown() must not be optimized away even when
 # the file's owner and group already have the desired value.
@@ -96,7 +96,7 @@ chgrp $g1 f
 # ctime is more recent.  This is not a big deal;
 # this test works fine when the files are on a local file system (/tmp).
 chgrp '' f
-test "`ls -C -c -t f g`" = 'f  g' || \
+test "$(ls -C -c -t f g)" = 'f  g' || \
   {
     case $host_triplet in
       *openbsd*) echo ignoring known OpenBSD-specific chgrp failure 1>&2 ;;