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popen(3)
NAME
  popen - Initiates a pipe to a process

SYNOPSIS
  #include <stdio.h>

  FILE *popen(
	  const char *command,
	  const char *type );

LIBRARY
  Standard C Library (libc)

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  popen():  XPG4, XPG4-UNIX

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  command
      Points to a null-terminated string containing a shell command line.

  type
      Points to a null-terminated string containing an I/O mode.

DESCRIPTION
  The popen() function creates a pipe between the calling program and a shell
  command to be executed. It returns a pointer to a FILE structure for the
  stream.

  If the type parameter is the value r, the calling program can read from the
  standard output of the command by reading from the returned file stream. If
  the type parameter is the value w, the calling program can write to the
  standard input of the command by writing to the returned file stream.

  Because open files are shared, a type r command can be used as an input
  filter and a type w command as an output filter.

NOTES
  Programs using the popen() function to invoke an output filter should
  beware of possible deadlock caused by output data remaining in the
  program's buffer. This can be avoided by either using the setbuf() function
  to ensure that the output stream is unbuffered, or by using the fflush()
  function to ensure that all buffered data is flushed before calling the
  pclose() function.

				    Caution

       If the original processes and the process started with the popen()
       function concurrently read or write a common file, neither should use
       buffered I/O. If they do, the results are unpredictable.

RETURN VALUES
  Upon successful completion, the popen() function returns a pointer to the
  FILE structure for the opened stream. In case of error because files or
  processes could not be created, the popen() function returns a null
  pointer.

SEE ALSO
  Functions: exec(2), fork(2), fclose(3), fopen(3), pclose(3), pipe(2),
  setbuf(3)

  Standards: standards(5)

Index for Section 3

Alphabetical listing for P

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