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└─⟦a0efdde77⟧ Bits:30001252 EUUGD11 Tape, 1987 Spring Conference Helsinki
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.TH NSHPOPEN 3 "local"
.SH NAME
nshpopen, nshpclose \- initiate I/O to/from a process
.SH SYNOPSIS
.B #include <stdio.h>
.PP
.SM
.B FILE
.B *nshpopen(command, type)
.br
.B char *command, *type;
.PP
.B nshpclose(stream)
.br
.SM
.B FILE
.B *stream;
.SH DESCRIPTION
The arguments to 
.I nshpopen
are pointers to null-terminated strings containing respectively
a shell command line and an I/O mode, either "r" for reading or
"w" for writing.
It creates a pipe between the calling process and the command
to be executed.
The value returned is a stream pointer that can be used (as
appropriate) to write to the standard input of the command or
read from its standard output.
.PP
A stream opened by
.I nshpopen
should be closed by
.IR nshpclose ,
which waits for the associated process to terminate
and returns the exit status of the command.
.PP
Because open files are shared, a type "r" command may be used
as an input filter, and a type "w" as an output filter.
.PP
.I Nshpopen
breaks up the
.I command
argument string at spaces and tabs for the child process.
However, it does not invoke a shell, and does not
attempt any shell shell meta character parsing.
In particular, quoted white space will still cause argument seperation.
By avoiding calling a shell, pipe creation is a great deal quicker.
Also, by avoiding the (rather complicated) shell meta character
parsing, some types of bugs may be avoided.
This is important where the security of setuid programs is involved.
.SH "SEE ALSO"
pipe(2),
popen(3),
fopen(3S),
fclose(3S),
system(3),
wait(2),
sh(1)
.SH DIAGNOSTICS
.I Nshpopen
returns a null pointer if files or processes cannot be created,
or the shell cannot be accessed.
.PP
.I Nshpclose
returns \-1 if
.I stream
is not associated with an `nshpopened' command.
.SH BUGS
Buffered reading before opening an input filter
may leave the standard input of that filter mispositioned.
Similar problems with an output filter may be
forestalled by careful buffer flushing, for instance, with
.I fflush,
see
.IR fclose (3).
.LP
.I Nshpopen
does not call a shell to do it's work.
It does not attempt to process shell meta characters.
Thus, it does not treat quotes, I/O redirects, or file
name wildcard characters specially.
This is it's incompatibility with
.I popen(3).
.LP
This type of function should have been included with
.I popen(3)
in the standard I/O library.