common/spawn.c: add spawn_piped()

include/common/spawn.h

@@ -2,10 +2,34 @@
 #ifndef LABWC_SPAWN_H
 #define LABWC_SPAWN_H
 
+#include <sys/types.h>
+
 /**
  * spawn_async_no_shell - execute asynchronously
  * @command: command to be executed
  */
 void spawn_async_no_shell(char const *command);
 
+/**
+ * spawn_piped - execute asyncronously
+ * @command: command to be executed
+ * @pipe_fd: set to the read end of a pipe
+ *           connected to stdout of the command
+ *
+ * Notes:
+ * The returned pid_t has to be waited for to
+ * not produce zombies and the pipe_fd has to
+ * be closed. spawn_piped_close() can be used
+ * to ensure both.
+ */
+pid_t spawn_piped(const char *command, int *pipe_fd);
+
+/**
+ * spawn_piped_close - clean up a previous
+ *                     spawn_piped() process
+ * @pid: will be waitpid()'d for
+ * @pipe_fd: will be close()'d
+ */
+void spawn_piped_close(pid_t pid, int pipe_fd);
+
 #endif /* LABWC_SPAWN_H */