Quote paths with double quotes not single quotes

scp.py

@@ -14,20 +14,31 @@
 import types
 
 
-# this is quote from the shlex module, added in py3.3
-_find_unsafe = re.compile(br'[^\w@%+=:,./~-]').search
+# Based on POSIX:
+# https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
+_find_unsafe = re.compile(br'[\[\s\'|&;<>()$\\"*?#~=%]').search
 
 
 def _sh_quote(s):
-    """Return a shell-escaped version of the string `s`."""
+    """Return a POSIX shell-escaped version of the string `s`."""
     if not s:
         return b""
     if _find_unsafe(s) is None:
         return s
 
-    # use single quotes, and put single quotes into double quotes
-    # the string $'b is then quoted as '$'"'"'b'
-    return b"'" + s.replace(b"'", b"'\"'\"'") + b"'"
+    # For maximal portability with Windows use double-quotes not single-
+    # quotes, and only escape the characters that are absolutely necessary.
+    # Note this does not provide 100% compatibility with Windows: if you need
+    # POSIX special characters $ or ` in your Windows path you'll need to
+    # provide your own sanitizer function.
+
+    # Take a match where group 1 is 0 or more backslashes and group 2 is a
+    # special character.  The result is the backslashes escaped, plus one
+    # backslash to escape the special character and the special character.
+    def esc(m):
+        return m.group(1) + m.group(1) + b'\\' + m.group(2)
+
+    return b'"' + re.sub(br'(\\*)([$`"\n])', esc, s) + b'"'
 
 
 # Unicode conversion functions; assume UTF-8

test.py

@@ -80,6 +80,7 @@ def setUpClass(cls):
             b'/tmp/r\\xC3\\xA9mi\\x00'
             b'/tmp/bien rang\\xC3\\xA9/file\\x00'
             b'/tmp/bien rang\\xC3\\xA9/b\\xC3\\xA8te\\x00'
+            b'/tmp/bien rang\\xC3\\xA9/h\\q\\$l\\`l\\"o\\x00'
             b'/tmp/p\\xE9t\\xE9'  # invalid UTF-8 here
             b'" | xargs -0 touch; '
             b'fi')
@@ -158,12 +159,13 @@ def test_get_folder(self):
                            [u'bien rang\xE9', u'bien rang\xE9\\file',
                             u'bien rang\xE9\\b\xE8te'],
                            [b'bien rang\xC3\xA9', b'bien rang\xC3\xA9/file',
-                            b'bien rang\xC3\xA9/b\xC3\xA8te'])
+                            b'bien rang\xC3\xA9/b\xC3\xA8te',
+                            b'bien rang\xC3\xA9/h\\q$l`l"o'])
         self.download_test(b'/tmp/bien rang\xC3\xA9', True, b'target',
                            [u'target', u'target\\file',
                             u'target\\b\xE8te'],
                            [b'target', b'target/file',
-                            b'target/b\xC3\xA8te'])
+                            b'target/b\xC3\xA8te', br'target/h\q$l`l"o'])
 
     def test_get_invalid_unicode(self):
         self.download_test(b'/tmp/p\xE9t\xE9', False, u'target',