Don't shell-parse REPL shell commands to make redirection etc. work

Julia's "shell parsing" (as used for backticks) excplicitly states that output redirection, pipes etc. are not supported via their shell metacharacters. Thus parsing a REPL shell command via the backtick mechanism makes it impossible to redirect output, unless shell quoting has loopholes and lets these metacharacters through (which leads to severe problems if one e.g. wants to quote an already-quoted string).

For example, Julia's shell parsing returns the same result for these two different commands:
   echo '>a'
   echo >a
In both cases, the command ["echo", ">a"] is generated, assuming that the character ">" is not special. It is then impossible to extract the original REPL user's intention from this command. Thus the REPL needs to parse shell commands via `split`, which suffices to determine whether the command is `cd`. Everything else is left to the shell.

base/REPL.jl

@@ -727,11 +727,9 @@ function setup_interface(repl::LineEditREPL; hascolor = repl.hascolor, extra_rep
             (repl.envcolors ? Base.input_color : repl.input_color) : "",
         keymap_func_data = repl,
         complete = ShellCompletionProvider(repl),
-        # Transform "foo bar baz" into `foo bar baz` (shell quoting)
-        # and pass into Base.repl_cmd for processing (handles `ls` and `cd`
-        # special)
+        # Pass into Base.repl_cmd for processing (handles `cd` special)
         on_done = respond(repl, julia_prompt) do line
-            Expr(:call, :(Base.repl_cmd), macroexpand(Expr(:macrocall, symbol("@cmd"),line)), outstream(repl))
+            Base.repl_cmd(line, outstream(repl))
         end)
 
     ################################# Stage II #############################

base/client.jl

@@ -39,7 +39,7 @@ exit(n) = ccall(:jl_exit, Void, (Int32,), n)
 exit() = exit(0)
 quit() = exit()
 
-function repl_cmd(cmd, out)
+function repl_cmd(line, out)
     shell = shell_split(get(ENV,"JULIA_SHELL",get(ENV,"SHELL","/bin/sh")))
     # Note that we can't support the fish shell due to its lack of subshells
     #   See this for details: https://github.com/JuliaLang/julia/issues/4918
@@ -49,29 +49,35 @@ function repl_cmd(cmd, out)
         shell = "/bin/sh"
     end
 
-    if isempty(cmd.exec)
+    cmds = split(line)
+    if isempty(cmds)
         throw(ArgumentError("no cmd to execute"))
-    elseif cmd.exec[1] == "cd"
+    elseif cmds[1] == "cd"
         new_oldpwd = pwd()
-        if length(cmd.exec) > 2
+        if length(cmds) > 2
             throw(ArgumentError("cd method only takes one argument"))
-        elseif length(cmd.exec) == 2
-            dir = cmd.exec[2]
+        elseif length(cmds) == 2
+            dir = cmds[2]
             if dir == "-"
                 if !haskey(ENV, "OLDPWD")
                     error("cd: OLDPWD not set")
                 end
                 cd(ENV["OLDPWD"])
             else
-                cd(@windows? dir : readchomp(`$shell -c "echo $(shell_escape(dir))"`))
+                cmd = "echo $dir"
+                unixcmd = `$shell -c $cmd`
+                cd(@windows? dir : readchomp(unixcmd))
             end
         else
             cd()
         end
         ENV["OLDPWD"] = new_oldpwd
         println(out, pwd())
     else
-        run(ignorestatus(@windows? cmd : (isa(STDIN, TTY) ? `$shell -i -c "($(shell_escape(cmd))) && true"` : `$shell -c "($(shell_escape(cmd))) && true"`)))
+        ttyflag = isa(STDIN, TTY) ? "-i" : ""
+        unixcmd = `$shell $ttyflag -c $line`
+        wincmd = Cmd(Vector{ByteString}(shell_split(line)))
+        run(ignorestatus(@windows? wincmd : unixcmd))
     end
     nothing
 end