1PCLOSE(P) POSIX Programmer's Manual PCLOSE(P)
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6 pclose - close a pipe stream to or from a process
7
9 #include <stdio.h>
10 int pclose(FILE *stream);
12
15 The pclose() function shall close a stream that was opened by popen(),
16 wait for the command to terminate, and return the termination status of
17 the process that was running the command language interpreter. How‐
18 ever, if a call caused the termination status to be unavailable to
19 pclose(), then pclose() shall return -1 with errno set to [ECHILD] to
20 report this situation. This can happen if the application calls one of
21 the following functions:
22 * wait()
24 * waitpid() with a pid argument less than or equal to 0 or equal to
26 the process ID of the command line interpreter
27 * Any other function not defined in this volume of
29 IEEE Std 1003.1-2001 that could do one of the above
30 In any case, pclose() shall not return before the child process created
32 by popen() has terminated.
33 If the command language interpreter cannot be executed, the child ter‐
35 mination status returned by pclose() shall be as if the command lan‐
36 guage interpreter terminated using exit(127) or _exit(127).
37 The pclose() function shall not affect the termination status of any
39 child of the calling process other than the one created by popen() for
40 the associated stream.
41 If the argument stream to pclose() is not a pointer to a stream created
43 by popen(), the result of pclose() is undefined.
44
46 Upon successful return, pclose() shall return the termination status of
47 the command language interpreter. Otherwise, pclose() shall return -1
48 and set errno to indicate the error.
49
51 The pclose() function shall fail if:
52 ECHILD The status of the child process could not be obtained, as
54 described above.
55 The following sections are informative.
58
60 None.
61
63 None.
64
66 There is a requirement that pclose() not return before the child
67 process terminates. This is intended to disallow implementations that
68 return [EINTR] if a signal is received while waiting. If pclose()
69 returned before the child terminated, there would be no way for the
70 application to discover which child used to be associated with the
71 stream, and it could not do the cleanup itself.
72 If the stream pointed to by stream was not created by popen(), histori‐
74 cal implementations of pclose() return -1 without setting errno. To
75 avoid requiring pclose() to set errno in this case,
76 IEEE Std 1003.1-2001 makes the behavior unspecified. An application
77 should not use pclose() to close any stream that was not created by
78 popen().
79 Some historical implementations of pclose() either block or ignore the
81 signals SIGINT, SIGQUIT, and SIGHUP while waiting for the child process
82 to terminate. Since this behavior is not described for the pclose()
83 function in IEEE Std 1003.1-2001, such implementations are not conform‐
84 ing. Also, some historical implementations return [EINTR] if a signal
85 is received, even though the child process has not terminated. Such
86 implementations are also considered non-conforming.
87 Consider, for example, an application that uses:
89 popen("command", "r")
92 to start command, which is part of the same application. The parent
94 writes a prompt to its standard output (presumably the terminal) and
95 then reads from the popen()ed stream. The child reads the response from
96 the user, does some transformation on the response (pathname expansion,
97 perhaps) and writes the result to its standard output. The parent
98 process reads the result from the pipe, does something with it, and
99 prints another prompt. The cycle repeats. Assuming that both processes
100 do appropriate buffer flushing, this would be expected to work.
101 To conform to IEEE Std 1003.1-2001, pclose() must use waitpid(), or
103 some similar function, instead of wait().
104 The code sample below illustrates how the pclose() function might be
106 implemented on a system conforming to IEEE Std 1003.1-2001.
107 int pclose(FILE *stream)
110 {
111 int stat;
112 pid_t pid;
113 pid = <pid for process created for stream by popen()>
116 (void) fclose(stream);
117 while (waitpid(pid, &stat, 0) == -1) {
118 if (errno != EINTR){
119 stat = -1;
120 break;
121 }
122 }
123 return(stat);
124 }
125
127 None.
128
130 fork() , popen() , waitpid() , the Base Definitions volume of
131 IEEE Std 1003.1-2001, <stdio.h>
132
134 Portions of this text are reprinted and reproduced in electronic form
135 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
136 -- Portable Operating System Interface (POSIX), The Open Group Base
137 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
138 Electrical and Electronics Engineers, Inc and The Open Group. In the
139 event of any discrepancy between this version and the original IEEE and
140 The Open Group Standard, the original IEEE and The Open Group Standard
141 is the referee document. The original Standard can be obtained online
142 at http://www.opengroup.org/unix/online.html .
143IEEE/The Open Group 2003 PCLOSE(P)