[Overview][Constants][Types][Procedures and functions][Variables][Index] | Reference for unit 'oldlinux' (#rtl)

# POpen

Pipe file to standard input/output of program

## Declaration

Source position: line 0

`procedure POpen(`
`var F: text;`
`const Prog: string;`
`rw: Char`
`); procedure POpen(`
`var F: file;`
`const Prog: string;`
`rw: Char`
`);`

## Description

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 be reset or rewritten prior to using it. F can be of type Text or File. A file opened with POpen can be closed with Close, but also with PClose. The result is the same, but PClose returns the exit status of the command Cmd.

## Errors

Errors are reported in LinuxError and are essentially those of the Execve, Dup and AssignPipe commands.

## See also

AssignPipe |  | Create a set of pipe file handlers
PClose |  | Close file opened with POpen

## Example

    Program Example37;

    { Program to demonstrate the Popen function. }

    uses oldlinux;

    var f : text;
        i : longint;

    begin
      writeln ('Creating a shell script to which echoes its arguments');
      writeln ('and input back to stdout');
      assign (f,'test21a');
      rewrite (f);
      writeln (f,'#!/bin/sh');
      writeln (f,'echo this is the child speaking.... ');
      writeln (f,'echo got arguments \*"$*"\*');
      writeln (f,'cat');
      writeln (f,'exit 2');
      writeln (f);
      close (f);
      chmod ('test21a',octal (755));
      popen (f,'./test21a arg1 arg2','W');
      if linuxerror<>0 then
         writeln ('error from POpen : Linuxerror : ', Linuxerror);
      for i:=1 to 10 do
        writeln (f,'This is written to the pipe, and should appear on stdout.');
      Flush(f);
      Writeln ('The script exited with status : ',PClose (f));
      writeln;
      writeln ('Press <return> to remove shell script.');
      readln;
      assign (f,'test21a');
      erase (f)
    end.

Documentation generated on: Feb 26 2014