1 files changed, 60 insertions, 0 deletions
diff --git a/combine.c b/combine.c
new file mode 100644
index 0000000..4629ca7
--- /dev/null
+++ b/combine.c
@@ -0,0 +1,60 @@
+// SPDX-FileCopyrightText: 2024 Tomasz Kramkowski <tomasz@kramkow.ski>
+// SPDX-LicenseIdentifier: GPL-3.0-or-later
+
+// A tool to combine two files by replacing every instance of the character
+// sequence %s with the contents of the file named by the first argument.
+// This tool does not support escaping.
+
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static const char *argv0 = "combine";
+
+void dump(FILE *f)
+{
+	if (fseek(f, 0, SEEK_SET) != 0) {
+		fprintf(stderr, "%s: error: Failed to rewind inclusion file: %s",
+			argv0, strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+	int c;
+	while (c = fgetc(f), c != EOF) putchar(c);
+}
+
+int main(int argc, char **argv)
+{
+	if (argv[0] != NULL) argv0 = argv[0];
+	if (argc != 2) {
+		fprintf(stderr, "Usage: %s inclusion\n", argv0);
+		return EXIT_FAILURE;
+	}
+
+	FILE *inclusion = fopen(argv[1], "r");
+	if (inclusion == NULL) {
+		fprintf(stderr, "%s: error: Failed to open \"%s\": %s\n", argv0,
+			argv[1], strerror(errno));
+		return EXIT_FAILURE;
+	}
+
+	bool was_percent = false;
+	int c;
+	while (c = getchar(), c != EOF) {
+		if (was_percent) {
+			was_percent = false;
+			if (c == 's') {
+				dump(inclusion);
+			} else {
+				putchar('%');
+				putchar(c);
+			}
+		} else {
+			if (c == '%')
+				was_percent = true;
+			else
+				putchar(c);
+		}
+	}
+}