From b810fa6ab1d9d3fd7f6ac0b56a1e0e83a5c33b02 Mon Sep 17 00:00:00 2001
From: Aki <please@ignore.pl>
Date: Wed, 15 Jun 2022 18:03:03 +0200
Subject: Added partial implementation of head

---
 .gitignore |  1 +
 Makefile   |  2 +-
 head.c     | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+), 1 deletion(-)
 create mode 100644 head.c

diff --git a/.gitignore b/.gitignore
index f2bfd53..a2d3955 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,5 +2,6 @@
 cat
 fallocate
 false
+head
 ls
 true
diff --git a/Makefile b/Makefile
index 8694215..cd44d92 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 CFLAGS+=-std=c11 -Wall -Wextra -Wpedantic -D_POSIX_C_SOURCE=200809L
-UTILS=cat fallocate false ls true
+UTILS=cat fallocate false head ls true
 
 all: ${UTILS}
 
diff --git a/head.c b/head.c
new file mode 100644
index 0000000..b372a30
--- /dev/null
+++ b/head.c
@@ -0,0 +1,69 @@
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+
+int head(int fd, int lines, const char * name)
+{
+	static const size_t SIZE = 1024 * 4;
+	char buffer[SIZE];
+	while (lines > 0) {
+		const ssize_t available = read(fd, buffer, SIZE);
+		if (-1 == available) {
+			perror(name);
+			return 1;
+		}
+		if (0 == available)
+			return 0;
+		size_t offset = 0;
+		for (ssize_t n = 0; n < available; ++n) {
+			if (buffer[n] == '\n') {
+				lines--;
+				if (0 <= lines) {
+					const ssize_t res = write(1, buffer + offset, 1 + n - offset);
+					if (-1 == res) {
+						perror(name);
+						return 1;
+					}
+					offset = 1 + n;
+				}
+				if (0 >= lines)
+					return 0;
+			}
+		}
+		if (0 < lines) {
+			const ssize_t res = write(1, buffer + offset, available - offset);
+			if (-1 == res) {
+				perror(name);
+				return 1;
+			}
+		}
+	}
+	return 0;
+}
+
+
+int main(int argc, char * argv[])
+{
+	int opt;
+	int lines = 10;
+	while (-1 != (opt = getopt(argc, argv, "n:"))) {
+		switch (opt) {
+		case 'n':
+			errno = 0;
+			lines = strtol(optarg, (char **) NULL, 10);
+			if (lines < 0)
+				errno = EINVAL;
+			if (0 != errno) {
+				perror(optarg);
+				return 1;
+			}
+			break;
+		default:
+			dprintf(2, "Usage: %s [-n lines] [file...]\n", argv[0]);
+			return 1;
+		}
+	}
+	(void) head(0, lines, "<stdin>");
+}
-- 
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