diff --git a/src/evalfunc.c b/src/evalfunc.c
index d2cc8fc..1b629ff 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -2369,6 +2369,8 @@
 			ret_number_bool,    f_setcharpos},
     {"setcharsearch",	1, 1, FEARG_1,	    arg1_dict_any,
 			ret_void,	    f_setcharsearch},
+    {"setcmdline",	1, 2, FEARG_1,	    arg2_string_number,
+			ret_number_bool,    f_setcmdline},
     {"setcmdpos",	1, 1, FEARG_1,	    arg1_number,
 			ret_number_bool,    f_setcmdpos},
     {"setcursorcharpos", 1, 3, FEARG_1,	    arg13_cursor,
@@ -3607,7 +3609,6 @@
 f_deepcopy(typval_T *argvars, typval_T *rettv)
 {
     varnumber_T	noref = 0;
-    int		copyID;
 
     if (in_vim9script()
 	    && (check_for_opt_bool_arg(argvars, 1) == FAIL))
@@ -3618,10 +3619,8 @@
     if (noref < 0 || noref > 1)
 	semsg(_(e_using_number_as_bool_nr), noref);
     else
-    {
-	copyID = get_copyID();
-	item_copy(&argvars[0], rettv, TRUE, TRUE, noref == 0 ? copyID : 0);
-    }
+	item_copy(&argvars[0], rettv, TRUE, TRUE,
+						noref == 0 ? get_copyID() : 0);
 }
 
 /*
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 2ef66ab..587a9ff 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -4211,6 +4211,35 @@
     rettv->vval.v_number = get_cmdline_screen_pos() + 1;
 }
 
+// Set the command line str to "str".
+// Returns 1 when failed, 0 when OK.
+    int
+set_cmdline_str(char_u *str, int pos)
+{
+    cmdline_info_T  *p = get_ccline_ptr();
+    int		    cmdline_type;
+    int		    len;
+
+    if (p == NULL)
+	return 1;
+
+    len = (int)STRLEN(str);
+    realloc_cmdbuff(len + 1);
+    p->cmdlen = len;
+    STRCPY(p->cmdbuff, str);
+
+    p->cmdpos = pos < 0 || pos > p->cmdlen ? p->cmdlen : pos;
+    new_cmdpos = p->cmdpos;
+
+    redrawcmd();
+
+    // Trigger CmdlineChanged autocommands.
+    cmdline_type = ccline.cmdfirstc == NUL ? '-' : ccline.cmdfirstc;
+    trigger_cmd_autocmd(cmdline_type, EVENT_CMDLINECHANGED);
+
+    return 0;
+}
+
 /*
  * Set the command line byte position to "pos".  Zero is the first position.
  * Only works when the command line is being edited.
@@ -4234,6 +4263,35 @@
     return 0;
 }
 
+// "setcmdline()" function
+    void
+f_setcmdline(typval_T *argvars, typval_T *rettv)
+{
+    int pos = -1;
+
+    if (argvars[0].v_type != VAR_STRING || argvars[0].vval.v_string == NULL)
+    {
+	emsg(_(e_string_required));
+	return;
+    }
+
+    if (argvars[1].v_type != VAR_UNKNOWN)
+    {
+	int error = FALSE;
+
+	pos = (int)tv_get_number_chk(&argvars[1], &error) - 1;
+	if (error)
+	    return;
+	if (pos < 0)
+	{
+	    emsg(_(e_argument_must_be_positive));
+	    return;
+	}
+    }
+
+    rettv->vval.v_number = set_cmdline_str(argvars[0].vval.v_string, pos);
+}
+
 /*
  * "setcmdpos()" function
  */
diff --git a/src/proto/ex_getln.pro b/src/proto/ex_getln.pro
index bcc310c..2eb32ab 100644
--- a/src/proto/ex_getln.pro
+++ b/src/proto/ex_getln.pro
@@ -34,6 +34,8 @@
 void f_getcmdline(typval_T *argvars, typval_T *rettv);
 void f_getcmdpos(typval_T *argvars, typval_T *rettv);
 void f_getcmdscreenpos(typval_T *argvars, typval_T *rettv);
+int set_cmdline_str(char_u *str, int pos);
+void f_setcmdline(typval_T *argvars, typval_T *rettv);
 void f_setcmdpos(typval_T *argvars, typval_T *rettv);
 void f_getcmdtype(typval_T *argvars, typval_T *rettv);
 int get_cmdline_firstc(void);
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 3372e8d..121ff25 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -3262,4 +3262,44 @@
   set wildoptions& wildmenu&
 endfunc
 
+func Test_setcmdline()
+  func SetText(text, pos)
+    call assert_equal(0, setcmdline(a:text))
+    call assert_equal(a:text, getcmdline())
+    call assert_equal(len(a:text) + 1, getcmdpos())
+
+    call assert_equal(0, setcmdline(a:text, a:pos))
+    call assert_equal(a:text, getcmdline())
+    call assert_equal(a:pos, getcmdpos())
+
+    call assert_fails('call setcmdline("' .. a:text .. '", -1)', 'E487:')
+    call assert_fails('call setcmdline({}, 0)', 'E928:')
+    call assert_fails('call setcmdline("' .. a:text .. '", {})', 'E728:')
+
+    return ''
+  endfunc
+
+  call feedkeys(":\<C-R>=SetText('set rtp?', 2)\<CR>\<CR>", 'xt')
+  call assert_equal('set rtp?', @:)
+
+  " setcmdline() returns 1 when not editing the command line.
+  call assert_equal(1, 'foo'->setcmdline())
+
+  " Called in custom function
+  func CustomComplete(A, L, P)
+    call assert_equal(0, setcmdline("DoCmd "))
+    return "January\nFebruary\nMars\n"
+  endfunc
+
+  com! -nargs=* -complete=custom,CustomComplete DoCmd :
+  call feedkeys(":DoCmd \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"DoCmd January February Mars', @:)
+
+  " Called in <expr>
+  cnoremap <expr>a setcmdline('let foo=')
+  call feedkeys(":a\<CR>", 'tx')
+  call assert_equal('let foo=0', @:)
+  cunmap a
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 931fe67..227e28c 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -3657,6 +3657,12 @@
   assert_equal(d, getcharsearch())
 enddef
 
+def Test_setcmdline()
+  v9.CheckDefAndScriptSuccess(['setcmdline("ls", 2)'])
+  v9.CheckDefAndScriptFailure(['setcmdline(123)'], ['E1013: Argument 1: type mismatch, expected string but got number', 'E928: String required'])
+  v9.CheckDefAndScriptFailure(['setcmdline("ls", "x")'], ['E1013: Argument 2: type mismatch, expected number but got string', 'E1030: Using a String as a Number'])
+enddef
+
 def Test_setcmdpos()
   v9.CheckDefAndScriptFailure(['setcmdpos("x")'], ['E1013: Argument 1: type mismatch, expected number but got string', 'E1210: Number required for argument 1'])
 enddef
diff --git a/src/version.c b/src/version.c
index 2e48687..6b4bdfa 100644
--- a/src/version.c
+++ b/src/version.c
@@ -708,6 +708,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    285,
+/**/
     284,
 /**/
     283,