diff --git a/client/mysqltest.cc b/client/mysqltest.cc
index 10a59b0c4afda..f78b469d1608e 100644
--- a/client/mysqltest.cc
+++ b/client/mysqltest.cc
@@ -4614,9 +4614,12 @@ void do_write_file_command(struct st_command *command, my_bool append)
   static DYNAMIC_STRING ds_content;
   static DYNAMIC_STRING ds_filename;
   static DYNAMIC_STRING ds_delimiter;
+  static DYNAMIC_STRING ds_eval_flag;
+  my_bool eval_content;
   const struct command_arg write_file_args[] = {
     { "filename", ARG_STRING, TRUE, &ds_filename, "File to write to" },
-    { "delimiter", ARG_STRING, FALSE, &ds_delimiter, "Delimiter to read until" }
+    { "delimiter", ARG_STRING, FALSE, &ds_delimiter, "Delimiter to read until" },
+    { "eval", ARG_STRING, FALSE, &ds_eval_flag, "Evaluate the content" }
   };
   DBUG_ENTER("do_write_file");
 
@@ -4629,6 +4632,14 @@ void do_write_file_command(struct st_command *command, my_bool append)
   if (bad_path(ds_filename.str))
     DBUG_VOID_RETURN;
 
+  if ((eval_content= (ds_eval_flag.length != 0)) &&
+      strcasecmp(ds_eval_flag.str, "eval"))
+  {
+    report_or_die("Invalid argument '%s' to '%.*b', only 'eval' is allowed",
+                  ds_eval_flag.str, command->first_word_len, command->query);
+    DBUG_VOID_RETURN;
+  }
+
   if (!append && access(ds_filename.str, F_OK) == 0)
   {
     /* The file should not be overwritten */
@@ -4651,10 +4662,24 @@ void do_write_file_command(struct st_command *command, my_bool append)
   if (cur_block->ok)
   {
     DBUG_PRINT("info", ("Writing to file: %s", ds_filename.str));
-    str_to_file2(ds_filename.str, ds_content.str, ds_content.length, append);
+    if (eval_content)
+    {
+      /* Evaluate on every execution, keep command->content unevaluated */
+      DYNAMIC_STRING ds_eval_content;
+      if (init_dynamic_string(&ds_eval_content, "", ds_content.length + 256, 256))
+        die("Out of memory");
+      do_eval(&ds_eval_content, ds_content.str,
+              ds_content.str + ds_content.length, FALSE);
+      str_to_file2(ds_filename.str, ds_eval_content.str, ds_eval_content.length,
+                   append);
+      dynstr_free(&ds_eval_content);
+    }
+    else
+      str_to_file2(ds_filename.str, ds_content.str, ds_content.length, append);
   }
   dynstr_free(&ds_filename);
   dynstr_free(&ds_delimiter);
+  dynstr_free(&ds_eval_flag);
   DBUG_VOID_RETURN;
 }
 
@@ -4665,11 +4690,11 @@ void do_write_file_command(struct st_command *command, my_bool append)
   command	called command
 
   DESCRIPTION
-  write_file <file_name> [<delimiter>];
+  write_file <file_name> [<delimiter> [eval]];
   <what to write line 1>
   <...>
   < what to write line n>
-  EOF
+  <delimiter>
 
   --write_file <file_name>;
   <what to write line 1>
@@ -4680,6 +4705,9 @@ void do_write_file_command(struct st_command *command, my_bool append)
   Write everything between the "write_file" command and 'delimiter'
   to "file_name"
 
+  If 'eval' is given, variables and expressions in the content are
+  substituted. It requires <delimiter> to be given explicitly.
+
   NOTE! Will fail if <file_name> exists
 
   Default <delimiter> is EOF
@@ -4741,11 +4769,11 @@ void do_write_line(struct st_command *command)
   command	called command
 
   DESCRIPTION
-  append_file <file_name> [<delimiter>];
+  append_file <file_name> [<delimiter> [eval]];
   <what to write line 1>
   <...>
   < what to write line n>
-  EOF
+  <delimiter>
 
   --append_file <file_name>;
   <what to write line 1>
@@ -4756,6 +4784,9 @@ void do_write_line(struct st_command *command)
   Append everything between the "append_file" command
   and 'delimiter' to "file_name"
 
+  If 'eval' is given, variables and expressions in the content are
+  substituted. It requires <delimiter> to be given explicitly.
+
   Default <delimiter> is EOF
 
 */
diff --git a/mysql-test/main/mysqltest.result b/mysql-test/main/mysqltest.result
index 478ef82ca1fa0..46234ba89a258 100644
--- a/mysql-test/main/mysqltest.result
+++ b/mysql-test/main/mysqltest.result
@@ -989,4 +989,41 @@ select "foo\""bar";
 foo\"bar
 foo\"bar
 set sql_mode=default;
+#
+# MDEV-40353: append_file in mysqltest does not support variables
+#             and expressions substitution
+#
+# Without 'eval' the content is written as it is
+variable: $var
+expression: $(6*7)
+escaped: \$var
+a backslash: \\! echo foo
+undefined variable: $mdev_40353_not_set.
+# With 'eval' variables and expressions are substituted
+variable: foo
+expression: 42
+escaped: $var
+a backslash: \! echo foo
+undefined variable: .
+# a lone dollar sign is an error when evaluated
+mysqltest: At line 1: Empty variable
+# append_file with 'eval' and a not default delimiter
+variable: foo
+expression: 42
+escaped: $var
+a backslash: \! echo foo
+undefined variable: .
+appended: foo
+# The 'eval' argument is not case sensitive
+variable: foo
+# The content is evaluated on every execution of the command
+iteration 1
+iteration 2
+# Nothing is written and nothing is evaluated in a false block
+the false block has written nothing
+# 'eval' requires the delimiter to be given explicitly
+mysqltest: At line 1: End of file encountered before 'eval' delimiter was found
+# Only 'eval' is allowed as the third argument
+mysqltest: At line 1: Invalid argument 'junk' to 'write_file', only 'eval' is allowed
+# End of 10.6 tests
 End of tests
diff --git a/mysql-test/main/mysqltest.test b/mysql-test/main/mysqltest.test
index b545e3540403e..ba01acbf6c6c5 100644
--- a/mysql-test/main/mysqltest.test
+++ b/mysql-test/main/mysqltest.test
@@ -2954,6 +2954,111 @@ set sql_mode=no_backslash_escapes;
 select "foo\""bar";
 set sql_mode=default;
 
+--echo #
+--echo # MDEV-40353: append_file in mysqltest does not support variables
+--echo #             and expressions substitution
+--echo #
+
+--let $file= $MYSQLTEST_VARDIR/tmp/mdev_40353.txt
+--let $var= foo
+
+--echo # Without 'eval' the content is written as it is
+
+--write_file $file
+variable: $var
+expression: $(6*7)
+escaped: \$var
+a backslash: \\! echo foo
+undefined variable: $mdev_40353_not_set.
+EOF
+--cat_file $file
+--remove_file $file
+
+--echo # With 'eval' variables and expressions are substituted
+
+--write_file $file EOF eval
+variable: $var
+expression: $(6*7)
+escaped: \$var
+a backslash: \\! echo foo
+undefined variable: $mdev_40353_not_set.
+EOF
+--cat_file $file
+
+--echo # a lone dollar sign is an error when evaluated
+
+--let $script= $MYSQLTEST_VARDIR/tmp/mdev_40353_err.test
+--write_file $script END
+  --write_file $MYSQLTEST_VARDIR/tmp/mdev_40353_err.txt EOF eval
+  a lone dollar sign: $
+  EOF
+END
+--error 1
+--exec $MYSQL_TEST < $script 2>&1
+--remove_file $script
+
+--echo # append_file with 'eval' and a not default delimiter
+
+--append_file $file END eval
+appended: $var
+END
+--cat_file $file
+--remove_file $file
+
+--echo # The 'eval' argument is not case sensitive
+
+--write_file $file EOF EVAL
+variable: $var
+EOF
+--cat_file $file
+--remove_file $file
+
+--echo # The content is evaluated on every execution of the command
+
+--let $i= 0
+while ($i < 2)
+{
+  --inc $i
+  --append_file $file EOF eval
+iteration $i
+EOF
+}
+--cat_file $file
+--remove_file $file
+
+--echo # Nothing is written and nothing is evaluated in a false block
+
+# A lone dollar sign in the content would be an error if it was evaluated
+--let $i= 0
+while ($i < 1)
+{
+  --inc $i
+  if (0)
+  {
+    --write_file $file EOF eval
+$
+EOF
+  }
+}
+
+# write_file fails if the file exists, so it also checks that the
+# false block above has written nothing
+--write_file $file
+the false block has written nothing
+EOF
+--cat_file $file
+--remove_file $file
+
+--echo # 'eval' requires the delimiter to be given explicitly
+--error 1
+--exec echo "--write_file $file eval" | $MYSQL_TEST 2>&1
+
+--echo # Only 'eval' is allowed as the third argument
+--error 1
+--exec echo "--write_file $file EOF junk" | $MYSQL_TEST 2>&1
+
+--echo # End of 10.6 tests
+
 --echo End of tests
 
 # Wait till we reached the initial number of concurrent sessions