.\" Copyright 1991 The Regents of the University of California.
.\" %sccs.include.redist.roff%
.\" @(#)popen.3 6.4 (Berkeley) %G%
.Fn popen "const char *command" "const char *type"
.Fn pclose "FILE *stream"
a process by creating a pipe,
Since a pipe is by definition unidirectional, the
argument may specify only reading or writing, not both;
the resulting stream is correspondingly read-only or write-only.
argument is a pointer to a null-terminated string
containing a shell command line.
This command is passed to
flag; interpretation, if any, is performed by the shell.
argument is a pointer to a null-terminated string
save that it must be closed with
writes to the standard input of the command;
the command's standard output is the same as that of the process that called
unless this is altered by the command itself.
Conversely, reading from a
stream reads the command's standard output, and
the command's standard input is the same as that of the process that called
streams are fully buffered by default.
function waits for the associated process to terminate
and returns the exit status of the command
or if it cannot allocate memory.
function does not reliably set
Since the standard input of a command opened for reading
shares its seek offset with the process that called
if the original process has done a buffered read,
the command's input position may not be as expected.
Similarly, the output from a command opened for writing
may become intermingled with that of the original process.
The latter can be avoided by calling
Failure to execute the shell
is indistinguishable from the shell's failure to execute command,
or an immediate exit of the command.
The only hint is an exit status of 127.
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