New component: cat

Generically reads an arbitrary file natively.

Saves a few layers of execution in comparison to using `run_command`
with an argument like `cat ./file`.

components/cat.c

@@ -0,0 +1,32 @@
+/* See LICENSE file for copyright and license details. */
+#include <stdio.h>
+#include <string.h>
+
+#include "../slstatus.h"
+#include "../util.h"
+
+const char *
+cat(const char *path)
+{
+        char *f;
+        FILE *fp;
+
+        if (!(fp = fopen(path, "r"))) {
+                warn("fopen '%s':", path);
+                return NULL;
+        }
+
+        f = fgets(buf, sizeof(buf) - 1, fp);
+        if (fclose(fp) < 0) {
+                warn("fclose '%s':", path);
+                return NULL;
+        }
+        if (!f)
+                return NULL;
+
+        if ((f = strrchr(buf, '\n')))
+                f[0] = '\0';
+
+        return buf[0] ? buf : NULL;
+}
+