Don't allow specifying an fd with a caret redirection

For example, an argument 12345^ is a real argument, not a redirection
There's no reason to use ^ here instead of >, and it's annoying to git
users.

Fixes #1873

src/tokenizer.cpp

@@ -383,10 +383,11 @@ static size_t read_redirection_or_fd_pipe(const wchar_t *buff,
             }
         }
     }
-
+    
     // Either way we should have ended on the redirection character itself like '>'.
+    // Don't allow an fd with a caret redirection - see #1873
     wchar_t redirect_char = buff[idx++];  // note increment of idx
-    if (redirect_char == L'>' || redirect_char == L'^') {
+    if (redirect_char == L'>' || (redirect_char == L'^' && idx == 1)) {
         redirection_mode = TOK_REDIRECT_OUT;
         if (buff[idx] == redirect_char) {
             // Doubled up like ^^ or >>. That means append.

tests/test1.in

@@ -104,6 +104,9 @@ echo Test 5 $sta
 echo Test redirections
 begin ; echo output ; echo errput 1>&2  ; end 2>&1 | tee ../test/temp/tee_test.txt ; cat ../test/temp/tee_test.txt
 
+# Test that trailing ^ doesn't trigger redirection, see #1873
+echo caret_no_redirect 12345^
+
 # Verify that we can pipe something other than stdout
 # The first line should be printed, since we output to stdout but pipe stderr to /dev/null
 # The second line should not be printed, since we output to stderr and pipe it to /dev/null

tests/test1.out

@@ -25,6 +25,7 @@ errput
 output
 errput
 output
+caret_no_redirect 12345^
 is_stdout
 abc\ndef
 abc