env: add XONSH_SUPPRESS_WELCOME to suppress welcome msg (#5719)

add `XONSH_SUPPRESS_WELCOME` variable to suppress welcome msg

Co-authored-by: Gil Forsyth <gforsyth@users.noreply.github.com>

news/add-suppress-welcome-env.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* env: Added ``$XONSH_SUPPRESS_WELCOME`` variable to suppress the welcome message.
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>

xonsh/environ.py

@@ -1627,6 +1627,10 @@ class PromptSetting(Xettings):
         "For example, to have stderr appear on a red background, the "
         'prefix & postfix pair would be "{BACKGROUND_RED}" & "{RESET}".',
     )
+    XONSH_SUPPRESS_WELCOME = Var.with_default(
+        False,
+        "Suppresses the welcome message.",
+    )
 
 
 class PromptHistorySetting(Xettings):

xonsh/main.py

@@ -548,6 +548,7 @@ def main_xonsh(args):
             ignore_sigtstp()
             if (
                 env["XONSH_INTERACTIVE"]
+                and not env["XONSH_SUPPRESS_WELCOME"]
                 and sys.stdin.isatty()  # In case the interactive mode is forced but no tty (input from pipe).
                 and not any(os.path.isfile(i) for i in env["XONSHRC"])
                 and not any(os.path.isdir(i) for i in env["XONSHRC_DIR"])