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popen (3)
  • popen (3) ( Solaris man: Библиотечные вызовы )
  • >> popen (3) ( FreeBSD man: Библиотечные вызовы )
  • popen (3) ( Русские man: Библиотечные вызовы )
  • popen (3) ( Linux man: Библиотечные вызовы )
  • popen (3) ( POSIX man: Библиотечные вызовы )

  • BSD mandoc
     

    NAME

    
    
    popen
    
     
    pclose
    
     - process
    
    I/O
    
     
    

    LIBRARY

    Lb libc
    
     
    

    SYNOPSIS

       #include <stdio.h>
    FILE * popen (const char *command const char *type);
    int pclose (FILE *stream);
     

    DESCRIPTION

    The popen ();
    function ``opens'' a process by creating a bidirectional pipe forking, and invoking the shell. Any streams opened by previous popen ();
    calls in the parent process are closed in the new child process. Historically, popen ();
    was implemented with a unidirectional pipe; hence many implementations of popen ();
    only allow the Fa type argument to specify reading or writing, not both. Since popen ();
    is now implemented using a bidirectional pipe, the Fa type argument may request a bidirectional data flow. The Fa type argument is a pointer to a null-terminated string which must be `r' for reading, `w' for writing, or `r+' for reading and writing.

    The Fa command argument is a pointer to a null-terminated string containing a shell command line. This command is passed to /bin/sh using the -c flag; interpretation, if any, is performed by the shell.

    The return value from popen ();
    is a normal standard I/O stream in all respects save that it must be closed with pclose ();
    rather than fclose (.);
    Writing to such a stream writes to the standard input of the command; the command's standard output is the same as that of the process that called popen (,);
    unless this is altered by the command itself. Conversely, reading from a ``popened'' stream reads the command's standard output, and the command's standard input is the same as that of the process that called popen (.);

    Note that output popen ();
    streams are fully buffered by default.

    The pclose ();
    function waits for the associated process to terminate and returns the exit status of the command as returned by wait4(2).  

    RETURN VALUES

    The popen ();
    function returns NULL if the fork(2) or pipe(2) calls fail, or if it cannot allocate memory.

    The pclose ();
    function returns -1 if Fa stream is not associated with a ``popened'' command, if Fa stream already ``pclosed'' or if wait4(2) returns an error.  

    ERRORS

    The popen ();
    function does not reliably set errno  

    SEE ALSO

    sh(1), fork(2), pipe(2), wait4(2), fclose(3), fflush(3), fopen(3), stdio(3), system(3)  

    HISTORY

    A popen ();
    and a pclose ();
    function appeared in AT&T System v7 .

    Bidirectional functionality was added in Fx 2.2.6 .  

    BUGS

    Since the standard input of a command opened for reading shares its seek offset with the process that called popen (,);
    if the original process has done a buffered read, the command's input position may not be as expected. Similarly, the output from a command opened for writing may become intermingled with that of the original process. The latter can be avoided by calling fflush(3) before popen (.);

    Failure to execute the shell is indistinguishable from the shell's failure to execute command, or an immediate exit of the command. The only hint is an exit status of 127.

    The popen ();
    function always calls sh(1), never calls csh(1).


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    ERRORS
    SEE ALSO
    HISTORY
    BUGS


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