add tail

util/concat.c

@@ -0,0 +1,17 @@
+/* See LICENSE file for copyright and license details. */
+#include <stdio.h>
+#include "../text.h"
+#include "../util.h"
+
+void
+concat(FILE *fp1, const char *s1, FILE *fp2, const char *s2)
+{
+	char buf[BUFSIZ];
+	size_t n;
+
+	while((n = fread(buf, 1, sizeof buf, fp1)) > 0)
+		if(fwrite(buf, 1, n, fp2) != n)
+			eprintf("%s: write error:", s2);
+	if(ferror(fp1))
+		eprintf("%s: read error:", s1);
+}