actually add the .c and .1 files

sponge.1

@@ -0,0 +1,15 @@
+.TH SPONGE 1 sbase\-VERSION
+.SH NAME
+sponge \- soak up standard input and write to a file
+.SH SYNOPSIS
+.B sponge
+.IR file
+.SH DESCRIPTION
+.B sponge
+reads stdin completely, then writes the saved contents to
+.IR file .
+This makes it possible to easily create pipes which read from and write to
+the same file.
+
+If the given file is a symbolic link, it writes to the links's destination
+instead.

sponge.c

@@ -0,0 +1,40 @@
+/* See LICENSE file for copyright and license details. */
+#include <stdio.h>
+
+#include "text.h"
+#include "util.h"
+
+static void
+usage(void)
+{
+	eprintf("usage: sponge file\n");
+}
+
+int
+main(int argc, char *argv[])
+{
+	FILE *fp, *tmpfp;
+
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND;
+
+	if(argc != 1)
+		usage();
+
+	if(!(tmpfp = tmpfile()))
+		eprintf("tmpfile:");
+
+	concat(stdin, "<stdin>", tmpfp, "<tmpfile>");
+	rewind(tmpfp);
+
+	if(!(fp = fopen(argv[0], "w")))
+		eprintf("sponge: '%s':", argv[0]);
+	concat(tmpfp, "<tmpfile>", fp, argv[0]);
+
+	fclose(fp);
+	fclose(tmpfp);
+
+	return 0;
+}