1PCLOSE(3P) POSIX Programmer's Manual PCLOSE(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 pclose - close a pipe stream to or from a process
13
15 #include <stdio.h>
16 int pclose(FILE *stream);
18
21 The pclose() function shall close a stream that was opened by popen(),
22 wait for the command to terminate, and return the termination status of
23 the process that was running the command language interpreter. How‐
24 ever, if a call caused the termination status to be unavailable to
25 pclose(), then pclose() shall return -1 with errno set to [ECHILD] to
26 report this situation. This can happen if the application calls one of
27 the following functions:
28 * wait()
30 * waitpid() with a pid argument less than or equal to 0 or equal to
32 the process ID of the command line interpreter
33 * Any other function not defined in this volume of
35 IEEE Std 1003.1-2001 that could do one of the above
36 In any case, pclose() shall not return before the child process created
38 by popen() has terminated.
39 If the command language interpreter cannot be executed, the child ter‐
41 mination status returned by pclose() shall be as if the command lan‐
42 guage interpreter terminated using exit(127) or _exit(127).
43 The pclose() function shall not affect the termination status of any
45 child of the calling process other than the one created by popen() for
46 the associated stream.
47 If the argument stream to pclose() is not a pointer to a stream created
49 by popen(), the result of pclose() is undefined.
50
52 Upon successful return, pclose() shall return the termination status of
53 the command language interpreter. Otherwise, pclose() shall return -1
54 and set errno to indicate the error.
55
57 The pclose() function shall fail if:
58 ECHILD The status of the child process could not be obtained, as
60 described above.
61 The following sections are informative.
64
66 None.
67
69 None.
70
72 There is a requirement that pclose() not return before the child
73 process terminates. This is intended to disallow implementations that
74 return [EINTR] if a signal is received while waiting. If pclose()
75 returned before the child terminated, there would be no way for the
76 application to discover which child used to be associated with the
77 stream, and it could not do the cleanup itself.
78 If the stream pointed to by stream was not created by popen(), histori‐
80 cal implementations of pclose() return -1 without setting errno. To
81 avoid requiring pclose() to set errno in this case,
82 IEEE Std 1003.1-2001 makes the behavior unspecified. An application
83 should not use pclose() to close any stream that was not created by
84 popen().
85 Some historical implementations of pclose() either block or ignore the
87 signals SIGINT, SIGQUIT, and SIGHUP while waiting for the child process
88 to terminate. Since this behavior is not described for the pclose()
89 function in IEEE Std 1003.1-2001, such implementations are not conform‐
90 ing. Also, some historical implementations return [EINTR] if a signal
91 is received, even though the child process has not terminated. Such
92 implementations are also considered non-conforming.
93 Consider, for example, an application that uses:
95 popen("command", "r")
98 to start command, which is part of the same application. The parent
100 writes a prompt to its standard output (presumably the terminal) and
101 then reads from the popen()ed stream. The child reads the response from
102 the user, does some transformation on the response (pathname expansion,
103 perhaps) and writes the result to its standard output. The parent
104 process reads the result from the pipe, does something with it, and
105 prints another prompt. The cycle repeats. Assuming that both processes
106 do appropriate buffer flushing, this would be expected to work.
107 To conform to IEEE Std 1003.1-2001, pclose() must use waitpid(), or
109 some similar function, instead of wait().
110 The code sample below illustrates how the pclose() function might be
112 implemented on a system conforming to IEEE Std 1003.1-2001.
113 int pclose(FILE *stream)
116 {
117 int stat;
118 pid_t pid;
119 pid = <pid for process created for stream by popen()>
122 (void) fclose(stream);
123 while (waitpid(pid, &stat, 0) == -1) {
124 if (errno != EINTR){
125 stat = -1;
126 break;
127 }
128 }
129 return(stat);
130 }
131
133 None.
134
136 fork(), popen(), waitpid(), the Base Definitions volume of
137 IEEE Std 1003.1-2001, <stdio.h>
138
140 Portions of this text are reprinted and reproduced in electronic form
141 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
142 -- Portable Operating System Interface (POSIX), The Open Group Base
143 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
144 Electrical and Electronics Engineers, Inc and The Open Group. In the
145 event of any discrepancy between this version and the original IEEE and
146 The Open Group Standard, the original IEEE and The Open Group Standard
147 is the referee document. The original Standard can be obtained online
148 at http://www.opengroup.org/unix/online.html .
149IEEE/The Open Group 2003 PCLOSE(3P)