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41 .Fn popen "const char *command" "const char *type"
43 .Fn pclose "FILE *stream"
49 a process by creating a bidirectional pipe
51 and invoking the shell.
52 Any streams opened by previous
54 calls in the parent process are closed in the new child process.
57 was implemented with a unidirectional pipe;
58 hence many implementations of
62 argument to specify reading or writing, not both.
65 is now implemented using a bidirectional pipe, the
67 argument may request a bidirectional data flow.
70 argument is a pointer to a null-terminated string
77 for reading and writing.
81 may be appended to that to request that the underlying file descriptor
86 argument is a pointer to a null-terminated string
87 containing a shell command line.
88 This command is passed to
92 flag; interpretation, if any, is performed by the shell.
98 stream in all respects
99 save that it must be closed with
103 Writing to such a stream
104 writes to the standard input of the command;
105 the command's standard output is the same as that of the process that called
107 unless this is altered by the command itself.
108 Conversely, reading from a
110 stream reads the command's standard output, and
111 the command's standard input is the same as that of the process that called
116 streams are fully buffered by default.
120 function waits for the associated process to terminate
121 and returns the exit status of the command
134 or if it cannot allocate memory.
141 is not associated with a
153 function does not reliably set
173 Bidirectional functionality was added in
176 Since the standard input of a command opened for reading
177 shares its seek offset with the process that called
179 if the original process has done a buffered read,
180 the command's input position may not be as expected.
181 Similarly, the output from a command opened for writing
182 may become intermingled with that of the original process.
183 The latter can be avoided by calling
188 Failure to execute the shell
189 is indistinguishable from the shell's failure to execute command,
190 or an immediate exit of the command.
191 The only hint is an exit status of 127.