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, 32 insertions, 32 deletions

diff --git a/tests/readlink/can-m b/tests/readlink/can-m
index d3e0b7c30..09a96f509 100755
--- a/tests/readlink/can-m
+++ b/tests/readlink/can-m
@@ -19,7 +19,7 @@
 . "${srcdir=.}/init.sh"; path_prepend_ ../src
 print_ver_ readlink
 
-pwd=`pwd`
+pwd=$(pwd)
 my_pwd=$("$abs_top_builddir/src/pwd")
 tmp=d
 
@@ -38,7 +38,7 @@ cd "$pwd/$tmp/removed" || framework_failure_
 
 # Skip this test if the system doesn't let you remove the working directory.
 if rmdir ../removed 2>/dev/null; then
-  v=`readlink -e .` && fail=1
+  v=$(readlink -e .) && fail=1
   test -z "$v" || fail=1
 fi
 
@@ -46,94 +46,94 @@ cd "$pwd/$tmp" || fail=1
 
 for p in "" "$pwd/$tmp/"; do
 
-  v=`readlink -m "${p}regfile"` || fail=1
+  v=$(readlink -m "${p}regfile") || fail=1
   test "$v" = "$my_pwd/$tmp/regfile" || fail=1
 
-  v=`readlink -m "${p}./regfile/"` || fail=1
+  v=$(readlink -m "${p}./regfile/") || fail=1
   test "$v" = "$my_pwd/$tmp/regfile" || fail=1
 
-  v=`readlink -m "${p}regfile/more"` || fail=1
+  v=$(readlink -m "${p}regfile/more") || fail=1
   test "$v" = "$my_pwd/$tmp/regfile/more" || fail=1
 
-  v=`readlink -m "${p}./regfile/more/"` || fail=1
+  v=$(readlink -m "${p}./regfile/more/") || fail=1
   test "$v" = "$my_pwd/$tmp/regfile/more" || fail=1
 
-  v=`readlink -m "${p}subdir"` || fail=1
+  v=$(readlink -m "${p}subdir") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir" || fail=1
 
-  v=`readlink -m "${p}./subdir/"` || fail=1
+  v=$(readlink -m "${p}./subdir/") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir" || fail=1
 
-  v=`readlink -m "${p}subdir/more"` || fail=1
+  v=$(readlink -m "${p}subdir/more") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir/more" || fail=1
 
-  v=`readlink -m "${p}./subdir/more/"` || fail=1
+  v=$(readlink -m "${p}./subdir/more/") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir/more" || fail=1
 
-  v=`readlink -m "${p}missing"` || fail=1
+  v=$(readlink -m "${p}missing") || fail=1
   test "$v" = "$my_pwd/$tmp/missing" || fail=1
 
-  v=`readlink -m "${p}./missing/"` || fail=1
+  v=$(readlink -m "${p}./missing/") || fail=1
   test "$v" = "$my_pwd/$tmp/missing" || fail=1
 
-  v=`readlink -m "${p}missing/more"` || fail=1
+  v=$(readlink -m "${p}missing/more") || fail=1
   test "$v" = "$my_pwd/$tmp/missing/more" || fail=1
 
-  v=`readlink -m "${p}./missing/more/"` || fail=1
+  v=$(readlink -m "${p}./missing/more/") || fail=1
   test "$v" = "$my_pwd/$tmp/missing/more" || fail=1
 
-  v=`readlink -m "${p}link1"` || fail=1
+  v=$(readlink -m "${p}link1") || fail=1
   test "$v" = "$my_pwd/$tmp/regfile" || fail=1
 
-  v=`readlink -m "${p}./link1/"` || fail=1
+  v=$(readlink -m "${p}./link1/") || fail=1
   test "$v" = "$my_pwd/$tmp/regfile" || fail=1
 
-  v=`readlink -m "${p}link1/more"` || fail=1
+  v=$(readlink -m "${p}link1/more") || fail=1
   test "$v" = "$my_pwd/$tmp/regfile/more" || fail=1
 
-  v=`readlink -m "${p}./link1/more/"` || fail=1
+  v=$(readlink -m "${p}./link1/more/") || fail=1
   test "$v" = "$my_pwd/$tmp/regfile/more" || fail=1
 
-  v=`readlink -m "${p}link2"` || fail=1
+  v=$(readlink -m "${p}link2") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir" || fail=1
 
-  v=`readlink -m "${p}./link2/"` || fail=1
+  v=$(readlink -m "${p}./link2/") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir" || fail=1
 
-  v=`readlink -m "${p}link2/more"` || fail=1
+  v=$(readlink -m "${p}link2/more") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir/more" || fail=1
 
-  v=`readlink -m "${p}./link2/more/"` || fail=1
+  v=$(readlink -m "${p}./link2/more/") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir/more" || fail=1
 
-  v=`readlink -m "${p}link2/more/more2"` || fail=1
+  v=$(readlink -m "${p}link2/more/more2") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir/more/more2" || fail=1
 
-  v=`readlink -m "${p}./link2/more/more2/"` || fail=1
+  v=$(readlink -m "${p}./link2/more/more2/") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir/more/more2" || fail=1
 
-  v=`readlink -m "${p}link3"` || fail=1
+  v=$(readlink -m "${p}link3") || fail=1
   test "$v" = "$my_pwd/$tmp/missing" || fail=1
 
-  v=`readlink -m "${p}./link3/"` || fail=1
+  v=$(readlink -m "${p}./link3/") || fail=1
   test "$v" = "$my_pwd/$tmp/missing" || fail=1
 
-  v=`readlink -m "${p}link3/more"` || fail=1
+  v=$(readlink -m "${p}link3/more") || fail=1
   test "$v" = "$my_pwd/$tmp/missing/more" || fail=1
 
-  v=`readlink -m "${p}./link3/more/"` || fail=1
+  v=$(readlink -m "${p}./link3/more/") || fail=1
   test "$v" = "$my_pwd/$tmp/missing/more" || fail=1
 
-  v=`readlink -m "${p}link4"` || fail=1
+  v=$(readlink -m "${p}link4") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir/missing" || fail=1
 
-  v=`readlink -m "${p}./link4/"` || fail=1
+  v=$(readlink -m "${p}./link4/") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir/missing" || fail=1
 
-  v=`readlink -m "${p}link4/more"` || fail=1
+  v=$(readlink -m "${p}link4/more") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir/missing/more" || fail=1
 
-  v=`readlink -m "${p}./link4/more/"` || fail=1
+  v=$(readlink -m "${p}./link4/more/") || fail=1
   test "$v" = "$my_pwd/$tmp/subdir/missing/more" || fail=1
 
 done