ulib uprintf to pipe not termdev, ulib Add stringbuffer and linearlist, tb Capture subshell output

ulib/string/stringbuffer.c

@@ -0,0 +1,26 @@
+#include <stdint.h>
+#include <stddef.h>
+#include <string/stringbuffer.h>
+#include <umalloc/umalloc.h>
+#include <string/string.h>
+#include <linearlist.h>
+
+void stringbuffer_init(StringBuffer *sb) {
+  string_memset(sb, 0, sizeof(*sb));
+}
+
+void stringbuffer_free(StringBuffer *sb) {
+  LINLIST_FREE(sb);
+}
+
+void stringbuffer_appendchar(StringBuffer *sb, char c) {
+  LINLIST_APPEND(sb, c);
+}
+
+void stringbuffer_appendcstr(StringBuffer *sb, char *cstr) {
+  char *s = cstr;
+  while (*s) {
+    stringbuffer_appendchar(sb, *s);
+    s++;
+  }
+}