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28 .\" @(#)popen.3 8.2 (Berkeley) 5/3/95
29 .\" $FreeBSD: src/lib/libc/gen/popen.3,v 1.10.2.4 2003/03/15 15:11:05 trhodes Exp $
30 .\" $DragonFly: src/lib/libc/gen/popen.3,v 1.4 2006/04/08 08:17:06 swildner Exp $
45 .Fn popen "const char *command" "const char *type"
47 .Fn pclose "FILE *stream"
53 a process by creating a bidirectional pipe
55 and invoking the shell.
56 Any streams opened by previous
58 calls in the parent process are closed in the new child process.
61 was implemented with a unidirectional pipe;
62 hence many implementations of
66 argument to specify reading or writing, not both.
69 is now implemented using a bidirectional pipe, the
71 argument may request a bidirectional data flow.
74 argument is a pointer to a null-terminated string
81 for reading and writing.
85 argument is a pointer to a null-terminated string
86 containing a shell command line.
87 This command is passed to
91 flag; interpretation, if any, is performed by the shell.
97 stream in all respects
98 save that it must be closed with
102 Writing to such a stream
103 writes to the standard input of the command;
104 the command's standard output is the same as that of the process that called
106 unless this is altered by the command itself.
107 Conversely, reading from a
109 stream reads the command's standard output, and
110 the command's standard input is the same as that of the process that called
115 streams are fully buffered by default.
119 function waits for the associated process to terminate
120 and returns the exit status of the command
133 or if it cannot allocate memory.
140 is not associated with a
152 function does not reliably set
172 Bidirectional functionality was added in
175 Since the standard input of a command opened for reading
176 shares its seek offset with the process that called
178 if the original process has done a buffered read,
179 the command's input position may not be as expected.
180 Similarly, the output from a command opened for writing
181 may become intermingled with that of the original process.
182 The latter can be avoided by calling
187 Failure to execute the shell
188 is indistinguishable from the shell's failure to execute command,
189 or an immediate exit of the command.
190 The only hint is an exit status of 127.