sh: Do not stat() $MAIL/$MAILPATH in non-interactive shells.

These may be NFS mounted, and we should not touch them unless we are going
to do something useful with the information.

bin/sh/main.c

@@ -157,6 +157,8 @@ main(int argc, char *argv[])
 		out2fmt_flush("sh: cannot determine working directory\n");
 	if (getpwd() != NULL)
 		setvar ("PWD", getpwd(), VEXPORT);
+	if (iflag)
+		chkmail(1);
 	if (argv[0] && argv[0][0] == '-') {
 		state = 1;
 		read_profile("/etc/profile");

bin/sh/var.c

@@ -337,8 +337,13 @@ setvareq(char *s, int flags)
 			/*
 			 * We could roll this to a function, to handle it as
 			 * a regular variable function callback, but why bother?
+			 *
+			 * Note: this assumes iflag is not set to 1 initially.
+			 * As part of init(), this is called before arguments
+			 * are looked at.
 			 */
-			if (vp == &vmpath || (vp == &vmail && ! mpathset()))
+			if ((vp == &vmpath || (vp == &vmail && ! mpathset())) &&
+			    iflag == 1)
 				chkmail(1);
 			if ((vp->flags & VEXPORT) && localevar(s)) {
 				change_env(s, 1);

tools/regression/bin/sh/parameters/mail1.0

@@ -0,0 +1,15 @@
+# $FreeBSD$
+# Test that a non-interactive shell does not access $MAIL.
+
+goodfile=/var/empty/sh-test-goodfile
+mailfile=/var/empty/sh-test-mailfile
+T=$(mktemp sh-test.XXXXXX) || exit
+MAIL=$mailfile ktrace -i -f "$T" sh -c "[ -s $goodfile ]" 2>/dev/null
+if ! grep -q $goodfile "$T"; then
+	# ktrace problem
+	rc=0
+elif ! grep -q $mailfile "$T"; then
+	rc=0
+fi
+rm "$T"
+exit ${rc:-3}

tools/regression/bin/sh/parameters/mail2.0

@@ -0,0 +1,15 @@
+# $FreeBSD$
+# Test that an interactive shell accesses $MAIL.
+
+goodfile=/var/empty/sh-test-goodfile
+mailfile=/var/empty/sh-test-mailfile
+T=$(mktemp sh-test.XXXXXX) || exit
+MAIL=$mailfile ktrace -i -f "$T" sh +m -i </dev/null >/dev/null 2>&1
+if ! grep -q $goodfile "$T"; then
+	# ktrace problem
+	rc=0
+elif grep -q $mailfile "$T"; then
+	rc=0
+fi
+rm "$T"
+exit ${rc:-3}