Add head

apps/head.c

@@ -0,0 +1,72 @@
+/* vim: tabstop=4 shiftwidth=4 noexpandtab
+ * This file is part of ToaruOS and is released under the terms
+ * of the NCSA / University of Illinois License - see LICENSE.md
+ * Copyright (C) 2018 K. Lange
+ *
+ * head - Print the first `n` lines of a file.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <getopt.h>
+#include <errno.h>
+
+int main(int argc, char * argv[]) {
+	int n = 10;
+	int opt;
+	int print_names = 0;
+	int retval = 0;
+
+	while ((opt = getopt(argc, argv, "n:")) != -1) {
+		switch (opt) {
+			case 'n':
+				n = atoi(optarg);
+				break;
+		}
+	}
+
+	if (argc > optind + 1) {
+		/* Multiple files */
+		print_names = 1;
+	}
+
+	if (argc == optind) {
+		/* This is silly, but should work due to reasons. */
+		argv[optind] = "-";
+		argc++;
+	}
+
+	for (int i = optind; i < argc; ++i) {
+		FILE * f = (!strcmp(argv[i],"-")) ? stdin : fopen(argv[i],"r");
+		if (!f) {
+			fprintf(stderr, "%s: %s: %s\n", argv[0], argv[i], strerror(errno));
+			retval = 1;
+			continue;
+		}
+
+		if (print_names) {
+			fprintf(stdout, "==> %s <==\n", (f == stdin) ? "standard input" : argv[i]);
+		}
+
+		int line = 1;
+
+		while (!feof(f)) {
+			int c = fgetc(f);
+			if (c >= 0) {
+				fputc(c, stdout);
+
+				if (c == '\n') {
+					line++;
+					if (line > n) break;
+				}
+			}
+		}
+
+		if (f != stdin) {
+			fclose(f);
+		}
+	}
+
+	return retval;
+}