2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
202 lines
4.8 KiB
Groff
202 lines
4.8 KiB
Groff
.\" $NetBSD: popen.3,v 1.16 2007/08/02 23:45:10 wiz Exp $
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.\"
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.\" Copyright (c) 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)popen.3 8.2 (Berkeley) 5/3/95
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.\"
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.Dd August 2, 2007
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.Dt POPEN 3
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.Os
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.Sh NAME
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.Nm popen ,
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.Nm pclose
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.Nd process
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.Tn I/O
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdio.h
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.Ft FILE *
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.Fn popen "const char *command" "const char *type"
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.Ft int
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.Fn pclose "FILE *stream"
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.Sh DESCRIPTION
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The
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.Fn popen
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function
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.Dq opens
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a process by creating an IPC connection,
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forking,
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and invoking the shell.
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Historically,
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.Nm popen
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was implemented with a unidirectional pipe;
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hence many implementations of
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.Nm popen
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only allow the
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.Fa type
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argument to specify reading or writing, not both.
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Since
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.Nm popen
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is now implemented using sockets, the
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.Fa type
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may request a bidirectional data flow.
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The
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.Fa type
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argument is a pointer to a null-terminated string
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which must be
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.Ql r
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for reading,
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.Ql w
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for writing, or
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.Ql r+
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for reading and writing.
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.Pp
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The
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.Fa command
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argument is a pointer to a null-terminated string
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containing a shell command line.
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This command is passed to
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.Pa /bin/sh
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using the
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.Fl c
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flag; interpretation, if any, is performed by the shell.
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.Pp
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The return value from
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.Fn popen
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is a normal standard
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.Tn I/O
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stream in all respects
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save that it must be closed with
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.Fn pclose
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rather than
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.Fn fclose .
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Writing to such a stream
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writes to the standard input of the command;
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the command's standard output is the same as that of the process that called
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.Fn popen ,
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unless this is altered by the command itself.
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Conversely, reading from a
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.Dq popened
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stream reads the command's standard output, and
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the command's standard input is the same as that of the process that called
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.Fn popen .
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.Pp
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Note that output
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.Fn popen
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streams are fully buffered by default.
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.Pp
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The
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.Fn pclose
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function waits for the associated process to terminate
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and returns the exit status of the command
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as returned by
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.Fn wait4 .
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.Sh RETURN VALUES
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The
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.Fn popen
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function returns
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.Dv NULL
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if the
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.Xr fork 2 ,
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.Xr pipe 2 ,
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or
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.Xr socketpair 2
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calls fail,
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or if it cannot allocate memory.
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.Pp
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The
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.Fn pclose
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function
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returns \-1 if
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.Fa stream
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is not associated with a
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.Dq popened
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command, if
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.Fa stream
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has already been
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.Dq pclosed ,
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or if
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.Xr wait4 2
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returns an error.
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.Sh ERRORS
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The
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.Fn popen
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function does not reliably set
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.Va errno .
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.Sh SEE ALSO
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.Xr sh 1 ,
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.Xr fork 2 ,
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.Xr pipe 2 ,
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.Xr socketpair 2 ,
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.Xr wait4 2 ,
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.Xr fclose 3 ,
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.Xr fflush 3 ,
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.Xr fopen 3 ,
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.Xr shquote 3 ,
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.Xr stdio 3 ,
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.Xr system 3
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.Sh STANDARDS
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The
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.Fn popen
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and
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.Fn pclose
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functions conform to
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.St -p1003.2-92 .
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.Sh HISTORY
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A
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.Fn popen
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and a
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.Fn pclose
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function appeared in
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.At v7 .
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.Sh BUGS
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Since the standard input of a command opened for reading
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shares its seek offset with the process that called
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.Fn popen ,
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if the original process has done a buffered read,
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the command's input position may not be as expected.
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Similarly, the output from a command opened for writing
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may become intermingled with that of the original process.
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The latter can be avoided by calling
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.Xr fflush 3
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before
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.Fn popen .
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.Pp
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Failure to execute the shell
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is indistinguishable from the shell's failure to execute command,
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or an immediate exit of the command.
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The only hint is an exit status of 127.
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.Pp
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The
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.Fn popen
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argument
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always calls
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.Xr sh 1 ,
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never calls
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.Xr csh 1 .
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