diff --git a/src/uniq.c b/src/uniq.c
new file mode 100644
index 0000000..cb2f604
--- /dev/null
+++ b/src/uniq.c
@@ -0,0 +1,161 @@
+/* uniq.c */
+
+
+
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+
+#define OPTS_c 1
+#define OPTS_d 2
+#define OPTS_u 4
+
+
+/* uniq */
+/* PRE	if in == NULL then out == NULL too
+ * POST
+ * 	0	success
+ * 	else	error(s) occured */
+static int _uniq_error(char * message, int ret);
+static int _uniq_do(int opts, char * fields, int chars,
+		FILE * infp, FILE * outfp);
+static int _uniq(int opts, char * fields, int chars, char * in, char * out)
+{
+	FILE * infp = stdin;
+	FILE * outfp = stdout;
+	int ret;
+
+	if(in != NULL && (infp = fopen(in, "r")) == NULL)
+		return _uniq_error(in, 2);
+	if(out != NULL && (outfp = fopen(out, "w")) == NULL)
+	{
+		fclose(infp);
+		return _uniq_error(out, 2);
+	}
+	ret = _uniq_do(opts, fields, chars, infp, outfp);
+	if(in == NULL)
+	{
+		fclose(infp);
+		if(out == NULL)
+			fclose(outfp);
+	}
+	return ret;
+}
+
+static int _uniq_error(char * message, int ret)
+{
+	fprintf(stderr, "%s", "uniq: ");
+	perror(message);
+	return ret;
+}
+
+static int _uniq_do(int opts, char * fields, int chars,
+		FILE * infp, FILE * outfp)
+{
+	char * lastline = NULL;
+	char * line = NULL;
+	int len = 0;
+	char * p;
+	unsigned int cnt = 1;
+#define BUF 80
+
+	for(;;)
+	{
+		if((p = realloc(line, sizeof(char) * (len + BUF))) == NULL)
+		{
+			free(lastline);
+			free(line);
+			return _uniq_error("malloc", 2);
+		}
+		line = p;
+		if(fgets(&line[len], BUF, infp) == NULL) /* FIXME */
+		{
+			free(lastline);
+			free(line);
+			return _uniq_error("fread", 2);
+		}
+		for(p = &line[len]; *p != '\0' && *p != '\n'; p++);
+		if(*p == '\0')
+		{
+			len += BUF;
+			continue;
+		}
+		*p = '\0';
+		if(lastline == NULL)
+		{
+			lastline = line;
+			line = NULL;
+			len = 0;
+			continue;
+		}
+		if(strcmp(lastline, line) == 0)
+		{
+			cnt++;
+			continue;
+		}
+		if(cnt == 1 && !(opts & OPTS_d)) /* line is not repeated */
+			printf("%s%s\n", opts & OPTS_c ? "1 " : "", lastline);
+		else if(cnt > 1 && !(opts & OPTS_u)) /* line is repeated */
+		{
+			if(opts & OPTS_c)
+				printf("%d ", cnt);
+			printf("%s\n", lastline);
+		}
+		free(lastline);
+		lastline = line;
+		line = NULL;
+		len = 0;
+		cnt = 1;
+	}
+	free(lastline);
+	free(line);
+	return 0;
+}
+
+
+/* usage */
+static int _usage(void)
+{
+	fprintf(stderr, "%s", "Usage: uniq [-c|-d|-u][-f fields][-s char]\
+[input_file [output_file]]\n");
+	return 1;
+}
+
+int main(int argc, char * argv[])
+{
+	int opts = 0;
+	char * fields = NULL;
+	int chars = 0;
+	char * in = NULL;
+	char * out = NULL;
+	int o;
+
+	while((o = getopt(argc, argv, "cduf:s:")) != -1)
+	{
+		switch(o)
+		{
+			case 'c':
+				opts |= OPTS_c;
+				break;
+			case 'd':
+				opts |= OPTS_d;
+				break;
+			case 'u':
+				opts |= OPTS_u;
+				break;
+			default:
+				return _usage();
+		}
+	}
+	if(argc - optind >= 1)
+	{
+		in = argv[optind];
+		if(argc - optind == 2)
+			out = argv[optind+1];
+		else if(argc - optind > 2)
+			return _usage();
+	}
+	return _uniq(opts, fields, chars, in, out);
+}