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

5 files changed, 11 insertions, 11 deletions

diff --git a/tests/touch/dangling-symlink b/tests/touch/dangling-symlink
index 576a302bb..1eb2ed38a 100755
--- a/tests/touch/dangling-symlink
+++ b/tests/touch/dangling-symlink
@@ -32,7 +32,7 @@ rm -f touch-target t-symlink
 if test $fail = 1; then
   case $host_triplet in
     *linux-gnu*)
-      case "`uname -r`" in
+      case "$(uname -r)" in
         2.3.9[0-9]*)
           skip_ \
 '****************************************************
diff --git a/tests/touch/empty-file b/tests/touch/empty-file
index cd679c41e..a150bd58e 100755
--- a/tests/touch/empty-file
+++ b/tests/touch/empty-file
@@ -48,7 +48,7 @@ echo sleeping for $SLEEP_SECONDS seconds...
 sleep $SLEEP_SECONDS
 for d in $TOUCH_DIR_LIST; do
   touch $d/a || fail=1
-  set x `ls -t $d/a $d/b`
+  set x $(ls -t $d/a $d/b)
   test "$*" = "x $d/a $d/b" || fail=1
 done
 
@@ -56,11 +56,11 @@ echo sleeping for $SLEEP_SECONDS seconds...
 sleep $SLEEP_SECONDS
 for d in $TOUCH_DIR_LIST; do
   touch $d/b
-  set x `ls -t $d/a $d/b`
+  set x $(ls -t $d/a $d/b)
   test "$*" = "x $d/b $d/a" || fail=1
 
   if touch - 1< $d/c 2> /dev/null; then
-    set x `ls -t $d/a $d/c`
+    set x $(ls -t $d/a $d/c)
     test "$*" = "x $d/c $d/a" || fail=1
   fi
 
diff --git a/tests/touch/no-dereference b/tests/touch/no-dereference
index 6f031424e..aee9a5cfc 100755
--- a/tests/touch/no-dereference
+++ b/tests/touch/no-dereference
@@ -58,11 +58,11 @@ esac
 
 # Change the mtime of a symlink.
 touch -m -h -d 2009-10-10 link || fail=1
-case `stat --format=%y link` in
+case $(stat --format=%y link) in
   2009-10-10*) ;;
   *) fail=1 ;;
 esac
-case `stat --format=%y file` in
+case $(stat --format=%y file) in
   2009-10-10*) fail=1;;
 esac
 
diff --git a/tests/touch/no-rights b/tests/touch/no-rights
index 25364e287..abebc5261 100755
--- a/tests/touch/no-rights
+++ b/tests/touch/no-rights
@@ -24,14 +24,14 @@ print_ver_ touch
 touch -d '2000-01-01 00:00' t1 || framework_failure_
 touch -d '2000-01-02 00:00' t2 || framework_failure_
 
-set x `ls -t t1 t2`
+set x $(ls -t t1 t2)
 test "$*" = "x t2 t1" || framework_failure_
 
 
 chmod 0 t1
 touch -d '2000-01-03 00:00' -c t1 || fail=1
 
-set x `ls -t t1 t2`
+set x $(ls -t t1 t2)
 test "$*" = "x t1 t2" || fail=1
 
 # Also test the combination of --no-create and -a.
diff --git a/tests/touch/trailing-slash b/tests/touch/trailing-slash
index f9c32fd7d..f09695c07 100755
--- a/tests/touch/trailing-slash
+++ b/tests/touch/trailing-slash
@@ -51,14 +51,14 @@ test -f nowhere && fail=1
 # symlinks and directories under Cygwin 1.5).
 touch -d 2009-10-10 -h link2/ || fail=1
 touch -h -r link2/ file || fail=1
-case `stat --format=%y dir` in
+case $(stat --format=%y dir) in
   2009-10-10*) ;;
   *) fail=1 ;;
 esac
-case `stat --format=%y link2` in
+case $(stat --format=%y link2) in
   2009-10-10*) fail=1 ;;
 esac
-case `stat --format=%y file` in
+case $(stat --format=%y file) in
   2009-10-10*) ;;
   *) fail=1 ;;
 esac