Add very simple ls

src/Makefile

@@ -1,6 +1,6 @@
 CC= gcc
-SRCFILES= cat.c touch.c yes.c mkdir.c echo.c
-OBJFILES= cat touch yes mkdir echo
+SRCFILES= cat.c touch.c yes.c mkdir.c echo.c ls.c
+OBJFILES= cat touch yes mkdir echo ls
 CFLAGS= -Wall -Wextra
 
 .PHONY: all clean
@@ -11,6 +11,7 @@ all:
 	$(CC) $(CFLAGS) yes.c -o yes
 	$(CC) $(CFLAGS) mkdir.c -o mkdir
 	$(CC) $(CFLAGS) echo.c -o echo
+	$(CC) $(CFLAGS) ls.c -o ls
 
 clean:
 	@rm ${OBJFILES}

src/ls.c

@@ -0,0 +1,32 @@
+#include <stdio.h>
+#include <dirent.h>
+
+// TODO: add more sorted output (. and .. in the top) and flags
+
+int main(int argc, char *argv[]) {
+  DIR *dp;
+  struct dirent *ep;
+  if (argc > 1) {
+    dp = opendir(argv[1]);
+    if (dp != NULL) {
+      while ((ep = readdir (dp))) {
+	printf("%s\n", ep->d_name);
+      }
+      closedir(dp);
+    } else {
+      perror("ls");
+    }
+    return 0;
+  } else {
+    dp = opendir("./");
+    if (dp != NULL) {
+      while ((ep = readdir (dp))) {
+	printf("%s\n", ep->d_name);
+      }
+      closedir(dp);
+    } else {
+      perror("ls");
+    }
+    return 0;
+  }
+}