diff --git a/mercurial/posix.py b/mercurial/posix.py
--- a/mercurial/posix.py
+++ b/mercurial/posix.py
@@ -8,7 +8,7 @@
 from i18n import _
 import encoding
 import os, sys, errno, stat, getpass, pwd, grp, socket, tempfile, unicodedata
-import fcntl
+import fcntl, re
 
 posixfile = open
 normpath = os.path.normpath
@@ -315,9 +315,16 @@ if sys.platform == 'cygwin':
     def checklink(path):
         return False
 
+_needsshellquote = None
 def shellquote(s):
     if os.sys.platform == 'OpenVMS':
         return '"%s"' % s
+    global _needsshellquote
+    if _needsshellquote is None:
+        _needsshellquote = re.compile(r'[^a-zA-Z0-9._/-]').search
+    if not _needsshellquote(s):
+        # "s" shouldn't have to be quoted
+        return s
     else:
         return "'%s'" % s.replace("'", "'\\''")
 
diff --git a/tests/test-extdiff.t b/tests/test-extdiff.t
--- a/tests/test-extdiff.t
+++ b/tests/test-extdiff.t
@@ -114,11 +114,11 @@ issue4463: usage of command line configu
   running '*echo* *\\a *\\a' in */extdiff.* (glob)
 #else
   $ hg --debug 4463a | grep '^running'
-  running '\'echo\' a-naked \'single quoted\' "double quoted" \'*/a\' \'$TESTTMP/a/a\'' in */extdiff.* (glob)
+  running 'echo a-naked \'single quoted\' "double quoted" */a $TESTTMP/a/a' in */extdiff.* (glob)
   $ hg --debug 4463b | grep '^running'
-  running 'echo b-naked \'single quoted\' "double quoted" \'*/a\' \'$TESTTMP/a/a\'' in */extdiff.* (glob)
+  running 'echo b-naked \'single quoted\' "double quoted" */a $TESTTMP/a/a' in */extdiff.* (glob)
   $ hg --debug echo | grep '^running'
-  running "'*echo*' '*/a' '$TESTTMP/a/a'" in */extdiff.* (glob)
+  running '*echo */a $TESTTMP/a/a' in */extdiff.* (glob)
 #endif
 
 (getting options from other than extdiff section)
@@ -149,15 +149,15 @@ issue4463: usage of command line configu
   running 'echo echo-naked "being quoted" *\\a *\\a' in */extdiff.* (glob)
 #else
   $ hg --debug 4463b2 | grep '^running'
-  running 'echo b2-naked \'single quoted\' "double quoted" \'*/a\' \'$TESTTMP/a/a\'' in */extdiff.* (glob)
+  running 'echo b2-naked \'single quoted\' "double quoted" */a $TESTTMP/a/a' in */extdiff.* (glob)
   $ hg --debug 4463b3 | grep '^running'
-  running 'echo b3-naked \'single quoted\' "double quoted" \'*/a\' \'$TESTTMP/a/a\'' in */extdiff.* (glob)
+  running 'echo b3-naked \'single quoted\' "double quoted" */a $TESTTMP/a/a' in */extdiff.* (glob)
   $ hg --debug 4463b4 | grep '^running'
-  running "echo '*/a' '$TESTTMP/a/a'" in */extdiff.* (glob)
-  $ hg --debug 4463b4 --option 'being quoted' | grep '^running'
-  running "echo 'being quoted' '*/a' '$TESTTMP/a/a'" in */extdiff.* (glob)
-  $ hg --debug extdiff -p echo --option 'being quoted' | grep '^running'
-  running "'echo' 'being quoted' '*/a' '$TESTTMP/a/a'" in */extdiff.* (glob)
+  running 'echo */a $TESTTMP/a/a' in */extdiff.* (glob)
+  $ hg --debug 4463b4 --option b4-naked --option 'being quoted' | grep '^running'
+  running "echo b4-naked 'being quoted' */a $TESTTMP/a/a" in */extdiff.* (glob)
+  $ hg --debug extdiff -p echo --option echo-naked --option 'being quoted' | grep '^running'
+  running "echo echo-naked 'being quoted' */a $TESTTMP/a/a" in */extdiff.* (glob)
 #endif
 
 #if execbit
@@ -273,7 +273,7 @@ Fallback to merge-tools.tool.executable|
   making snapshot of 2 files from working directory
     a
     b
-  running "'$TESTTMP/a/dir/tool.sh' 'a.*' 'a'" in */extdiff.* (glob)
+  running '$TESTTMP/a/dir/tool.sh a.* a' in */extdiff.* (glob)
   ** custom diff **
   cleaning up temp directory
   [1]