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28 .\" @(#)popen.3 8.2 (Berkeley) 5/3/95
44 .Fn popen "const char *command" "const char *type"
46 .Fn pclose "FILE *stream"
52 a process by creating a bidirectional pipe
54 and invoking the shell.
55 Any streams opened by previous
57 calls in the parent process are closed in the new child process.
60 was implemented with a unidirectional pipe;
61 hence many implementations of
65 argument to specify reading or writing, not both.
68 is now implemented using a bidirectional pipe, the
70 argument may request a bidirectional data flow.
73 argument is a pointer to a null-terminated string
80 for reading and writing.
84 argument is a pointer to a null-terminated string
85 containing a shell command line.
86 This command is passed to
90 flag; interpretation, if any, is performed by the shell.
96 stream in all respects
97 save that it must be closed with
101 Writing to such a stream
102 writes to the standard input of the command;
103 the command's standard output is the same as that of the process that called
105 unless this is altered by the command itself.
106 Conversely, reading from a
108 stream reads the command's standard output, and
109 the command's standard input is the same as that of the process that called
114 streams are fully buffered by default.
118 function waits for the associated process to terminate
119 and returns the exit status of the command
132 or if it cannot allocate memory.
139 is not associated with a
151 function does not reliably set
171 Bidirectional functionality was added in
174 Since the standard input of a command opened for reading
175 shares its seek offset with the process that called
177 if the original process has done a buffered read,
178 the command's input position may not be as expected.
179 Similarly, the output from a command opened for writing
180 may become intermingled with that of the original process.
181 The latter can be avoided by calling
186 Failure to execute the shell
187 is indistinguishable from the shell's failure to execute command,
188 or an immediate exit of the command.
189 The only hint is an exit status of 127.