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From: worley@alum.mit.edu (Dale R. Worley)
Newsgroups: gnu.bash.bug
Subject: An xtrace variant
Date: Sun, 28 Jun 2020 15:19:27 -0400
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Xref: csiph.com gnu.bash.bug:16472

When debugging a shell script, a useful command is:

    bash -x script-name

The deficiency of this is that "-x" causes all simple commands in your
startup files to be echoed as they are executed, and often this output
is a lot longer than the output from the commands in the script.

For a long time, I've wanted a variant of -x that only echoed the simple
commands after bash is done executing the startup files.  I finally did
a test implementation, naming a new switch "-X".  If it is set at the
end of the execution of the startup files, then bash sets "-x", which
causes subsequent simple commands to be echoed.

I named the new option "-X" as a mnemonic variant of "-x".  Its long
name is "Xtrace", because I couldn't think of anything better.  The code
changes are quite simple really.

Is this a useful idea?  Is there a better way to get an effect like
this?

Dale

diff --git a/builtins/set.def b/builtins/set.def
index d2bba43..e71c58f 100644
--- a/builtins/set.def
+++ b/builtins/set.def
@@ -114,6 +114,7 @@ Options:
           vi           use a vi-style line editing interface
 #endif /* READLINE */
           xtrace       same as -x
+          Xtrace       same as -X
   -p  Turned on whenever the real and effective user ids do not match.
       Disables processing of the $ENV file and importing of shell
       functions.  Turning this option off causes the effective uid and
@@ -122,6 +123,7 @@ Options:
   -u  Treat unset variables as an error when substituting.
   -v  Print shell input lines as they are read.
   -x  Print commands and their arguments as they are executed.
+  -X  Set -x after startup files are executed.
 #if defined (BRACE_EXPANSION)
   -B  the shell will perform brace expansion
 #endif /* BRACE_EXPANSION */
@@ -231,6 +233,7 @@ const struct {
   { "vi",        '\0', (int *)NULL, set_edit_mode, get_edit_mode },
 #endif
   { "xtrace",	  'x', (int *)NULL, (setopt_set_func_t *)NULL, (setopt_get_func_t *)NULL  },
+  { "Xtrace",	  'X', (int *)NULL, (setopt_set_func_t *)NULL, (setopt_get_func_t *)NULL  },
   {(char *)NULL, 0 , (int *)NULL, (setopt_set_func_t *)NULL, (setopt_get_func_t *)NULL },
 };
 
diff --git a/flags.c b/flags.c
index 6e20841..0828f78 100644
--- a/flags.c
+++ b/flags.c
@@ -159,6 +159,9 @@ int error_trace_mode = 0;
    with a 0 status, the status of the pipeline is 0. */
 int pipefail_opt = 0;
 
+/* Non-zero means set -x after startup files are executed. */
+int echo_commands_after_startup = 0;
+
 /* **************************************************************** */
 /*								    */
 /*			The Flags ALIST.			    */
@@ -187,7 +190,7 @@ const struct flags_alist shell_flags[] = {
   { 't', &just_one_command },
   { 'u', &unbound_vars_is_error },
   { 'v', &verbose_flag },
-  { 'x', &echo_command_at_execute },
+  { 'x', &echo_command_at_execute }, 
 
   /* New flags that control non-standard things. */
 #if 0
@@ -204,6 +207,7 @@ const struct flags_alist shell_flags[] = {
   { 'I', &no_invisible_vars },
   { 'P', &no_symbolic_links },
   { 'T', &function_trace_mode },
+  { 'X', &echo_commands_after_startup },
   {0, (int *)NULL}
 };
 
diff --git a/flags.h b/flags.h
index fdbf7f9..3b6fa8c 100644
--- a/flags.h
+++ b/flags.h
@@ -48,7 +48,8 @@ extern int
   echo_command_at_execute, no_invisible_vars, noclobber,
   hashing_enabled, forced_interactive, privileged_mode, jobs_m_flag,
   asynchronous_notification, interactive_comments, no_symbolic_links,
-  function_trace_mode, error_trace_mode, pipefail_opt;
+  function_trace_mode, error_trace_mode, pipefail_opt,
+  echo_commands_after_startup;
 
 /* -c, -s invocation options -- not really flags, but they show up in $- */
 extern int want_pending_command, read_from_stdin;
diff --git a/shell.c b/shell.c
index a2b2a55..4c40cd4 100644
--- a/shell.c
+++ b/shell.c
@@ -731,6 +731,10 @@ main (argc, argv, env)
 	start_debugger ();
 
 #if defined (ONESHOT)
+      if (echo_commands_after_startup) {
+	set_minus_o_option (FLAG_ON, "xtrace");
+	set_shellopts ();
+      }
       executing = 1;
       run_one_command (command_execution_string);
       exit_shell (last_command_exit_value);
@@ -791,6 +795,11 @@ main (argc, argv, env)
  read_and_execute:
 #endif /* !ONESHOT */
 
+  if (echo_commands_after_startup) {
+    set_minus_o_option (FLAG_ON, "xtrace");
+    set_shellopts ();
+  }
+
   shell_initialized = 1;
 
   if (pretty_print_mode && interactive_shell)