diff --git a/library/string.c b/library/string.c
new file mode 100644
index 0000000..4f32f5b
--- /dev/null
+++ b/library/string.c
@@ -0,0 +1,307 @@
+/*
+Copyright (C) 2015-2019 The University of Notre Dame
+This software is distributed under the GNU General Public License.
+See the file LICENSE for details.
+*/
+
+#include "kernel/types.h"
+#include "kernel/ascii.h"
+#include "library/malloc.h"
+#include "library/string.h"
+#include "library/malloc.h"
+#include "stdarg.h"
+
+void strcpy(char *d, const char *s)
+{
+	while(*s) {
+		*d++ = *s++;
+	}
+	*d = 0;
+}
+
+void strncpy(char *d, const char *s, unsigned length)
+{
+	while(*s && length--) {
+		*d++ = *s++;
+	}
+	*d = 0;
+}
+
+char * strdup(const char *s)
+{
+	char * d = (char *)malloc((strlen(s)+1) * sizeof(char));
+	char * tmp = d;
+	while(*s) {
+		*tmp++ = *s++;
+	}
+	*tmp = 0;
+	return d;
+}
+
+int strcmp(const char *a, const char *b)
+{
+	while(1) {
+		if(*a < *b) {
+			return -1;
+		} else if(*a > *b) {
+			return 1;
+		} else if(*a == 0) {
+			return 0;
+		} else {
+			a++;
+			b++;
+		}
+	}
+}
+
+int strncmp(const char *a, const char *b, unsigned length)
+{
+	while(length > 0) {
+		if(*a < *b) {
+			return -1;
+		} else if(*a > *b) {
+			return 1;
+		} else if(*a == 0) {
+			return 0;
+		} else {
+			a++;
+			b++;
+			length--;
+		}
+	}
+	return 0;
+}
+
+unsigned strlen(const char *s)
+{
+	unsigned len = 0;
+	while(*s) {
+		len++;
+		s++;
+	}
+	return len;
+}
+
+char *strrev(char *s)
+{
+	unsigned start = 0;
+	unsigned end = strlen(s) - 1;
+	char swap;
+
+	while(start < end) {
+		swap = s[start];
+		s[start] = s[end];
+		s[end] = swap;
+
+		start++;
+		end--;
+	}
+
+	return s;
+}
+
+char *strcat(char *d, const char *s)
+{
+	strcpy(d + strlen(d), s);
+	return d;
+}
+
+const char *strchr(const char *s, char ch)
+{
+	while(*s) {
+		if(*s == ch)
+			return s;
+		s++;
+	}
+	return 0;
+}
+
+char *strtok(char *s, const char *delim)
+{
+	static char *oldword = 0;
+	char *word;
+
+	if(!s)
+		s = oldword;
+
+	while(*s && strchr(delim, *s))
+		s++;
+
+	if(!*s) {
+		oldword = s;
+		return 0;
+	}
+
+	word = s;
+	while(*s && !strchr(delim, *s))
+		s++;
+
+	if(*s) {
+		*s = 0;
+		oldword = s + 1;
+	} else {
+		oldword = s;
+	}
+
+	return word;
+}
+
+int str2int(const char *s, int *d)
+{
+	int val = 0;
+	for(; *s; ++s) {
+		val *= 10;
+		if(*s > ASCII_9 || *s < ASCII_0) {
+			return 0;
+		}
+		val += (*s - '0');
+	}
+	*d = val;
+	return 1;
+}
+
+void memset(void *vd, char value, unsigned length)
+{
+	char *d = vd;
+	while(length) {
+		*d = value;
+		length--;
+		d++;
+	}
+}
+
+void memcpy(void *vd, const void *vs, unsigned length)
+{
+	char *d = vd;
+	const char *s = vs;
+	while(length) {
+		*d = *s;
+		d++;
+		s++;
+		length--;
+	}
+}
+
+extern void printf_putstring(const char *str);
+extern void printf_putchar(char c);
+
+static void printf_puthexdigit(uint8_t i)
+{
+	if(i < 10) {
+		printf_putchar('0' + i);
+	} else {
+		printf_putchar('a' + i - 10);
+	}
+}
+
+static void printf_puthex(uint32_t i)
+{
+	int j;
+	for(j = 28; j >= 0; j = j - 4) {
+		printf_puthexdigit((i >> j) & 0x0f);
+	}
+}
+
+static void printf_putint(int32_t i)
+{
+	int f, d;
+	if(i < 0 && i != 0) {
+		printf_putchar('-');
+		i = -i;
+	}
+
+	f = 1;
+	while((i / f) >= 10) {
+		f *= 10;
+	}
+	while(f > 0) {
+		d = i / f;
+		printf_putchar('0' + d);
+		i = i - d * f;
+		f = f / 10;
+	}
+}
+
+static void printf_putuint(uint32_t u)
+{
+	int f, d;
+	f = 1;
+	while((u / f) >= 10) {
+		f *= 10;
+	}
+	while(f > 0) {
+		d = u / f;
+		printf_putchar('0' + d);
+		u = u - d * f;
+		f = f / 10;
+	}
+}
+
+void printf(const char *s, ...)
+{
+	va_list args;
+
+	uint32_t u;
+	int32_t i;
+	char *str;
+
+	va_start(args, s);
+
+	while(*s) {
+		if(*s != '%') {
+			printf_putchar(*s);
+		} else {
+			s++;
+			switch (*s) {
+			case 'd':
+				i = va_arg(args, int32_t);
+				printf_putint(i);
+				break;
+			case 'u':
+				u = va_arg(args, uint32_t);
+				printf_putuint(u);
+				break;
+			case 'x':
+				u = va_arg(args, uint32_t);
+				printf_puthex(u);
+				break;
+			case 's':
+				str = va_arg(args, char *);
+				printf_putstring(str);
+				break;
+			case 'c':
+				u = va_arg(args, int32_t);
+				printf_putchar(u);
+				break;
+			case 0:
+				return;
+				break;
+			default:
+				printf_putchar(*s);
+				break;
+			}
+		}
+		s++;
+	}
+	va_end(args);
+}
+
+char *uint_to_string(uint32_t u, char *s)
+{
+	uint32_t f, d, i;
+
+	f = 1;
+	i = 0;
+	while((u / (f * 10)) > 0) {
+		f *= 10;
+	}
+	while(f > 0) {
+		d = u / f;
+		s[i] = '0' + d;
+		u = u % f;
+		f = f / 10;
+		i++;
+	}
+	s[i] = 0;
+	return s;
+}