You lose the fine control you once had by using the pipe() system call, and handling the fork/exec yourself. However, since the Bourne shell is used directly, shell metacharacter expansion (including wildcards) is permissible within the ”command” argument.Pipes which are created with popen() must be closed with pclose(). By now, you have probably realized that popen/pclose share a striking resemblance to the standard file stream I/O functions fopen() and fclose().
Author: Beniamin Suhayl