Procedure POpen (F : Text; Cmd : pathstr; rw : char) ;
Popen runs the command specified in Cmd, and redirects the standard in or output of the command to the other end of the pipe F. The parameter rw indicates the direction of the pipe. If it is set to 'W', then F can be used to write data, which will then be read by the command from stdinput. If it is set to 'R', then the standard output of the command can be read from F. F should NOT be reset or rewritten. .
Errors are reported in LinuxError and are essentially those of the Execve, Dup and AssignPipe commands.
AssignPipe, popen(3)