258 lines
6.6 KiB
Groff
258 lines
6.6 KiB
Groff
.\" $NetBSD: exec.3,v 1.18 2003/08/07 16:42:47 agc 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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.\" @(#)exec.3 8.3 (Berkeley) 1/24/94
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.\"
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.Dd August 10, 2002
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.Dt EXEC 3
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.Os
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.Sh NAME
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.Nm execl ,
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.Nm execlp ,
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.Nm execle ,
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.Nm exect ,
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.Nm execv ,
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.Nm execvp
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.Nd execute a file
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Vt extern char **environ;
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.Ft int
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.Fn execl "const char *path" "const char *arg" ...
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.Ft int
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.Fn execlp "const char *file" "const char *arg" ...
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.Ft int
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.Fn execle "const char *path" "const char *arg" ... "char *const envp[]"
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.Ft int
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.Fn exect "const char *path" "char *const argv[]" "char *const envp[]"
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.Ft int
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.Fn execv "const char *path" "char *const argv[]"
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.Ft int
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.Fn execvp "const char *file" "char *const argv[]"
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.Sh DESCRIPTION
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The
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.Nm exec
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family of functions replaces the current process image with a
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new process image.
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The functions described in this manual page are front-ends for the function
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.Xr execve 2 .
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(See the manual page for
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.Xr execve 2
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for detailed information about the replacement of the current process.)
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.Pp
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The initial argument for these functions is the pathname of a file which
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is to be executed.
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.Pp
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The
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.Fa "const char *arg"
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and subsequent ellipses in the
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.Fn execl ,
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.Fn execlp ,
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and
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.Fn execle
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functions can be thought of as
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.Em arg0 ,
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.Em arg1 ,
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\&...,
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.Em argn .
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Together they describe a list of one or more pointers to null-terminated
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strings that represent the argument list available to the executed program.
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The first argument, by convention, should point to the file name associated
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with the file being executed.
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The list of arguments
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.Em must
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be terminated by a
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.Dv NULL
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pointer.
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.Pp
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The
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.Fn exect ,
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.Fn execv ,
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and
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.Fn execvp
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functions provide an array of pointers to null-terminated strings that
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represent the argument list available to the new program.
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The first argument, by convention, should point to the file name associated
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with the file being executed.
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The array of pointers
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.Sy must
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be terminated by a
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.Dv NULL
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pointer.
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.Pp
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The
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.Fn execle
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and
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.Fn exect
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functions also specify the environment of the executed process by following
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the
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.Dv NULL
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pointer that terminates the list of arguments in the parameter list
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or the pointer to the argv array with an additional parameter.
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This additional parameter is an array of pointers to null-terminated strings
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and
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.Em must
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be terminated by a
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.Dv NULL
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pointer.
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The other functions take the environment for the new process image from the
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external variable
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.Va environ
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in the current process.
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.Pp
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Some of these functions have special semantics.
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.Pp
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The functions
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.Fn execlp
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and
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.Fn execvp
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will duplicate the actions of the shell in searching for an executable file
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if the specified file name does not contain a slash
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.Dq Li \&/
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character.
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The search path is the path specified in the environment by the
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.Ev PATH
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variable.
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If this variable isn't specified,
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.Va _PATH_DEFPATH
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from
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.Pa <paths.h>
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is used instead, its value being:
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.Pa /usr/bin:/bin:/usr/pkg/bin:/usr/local/bin .
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In addition, certain errors are treated specially.
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.Pp
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If permission is denied for a file (the attempted
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.Xr execve 2
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returned
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.Er EACCES ) ,
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these functions will continue searching the rest of
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the search path.
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If no other file is found, however, they will return with the global variable
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.Va errno
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set to
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.Er EACCES .
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.Pp
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If the header of a file isn't recognized (the attempted
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.Xr execve 2
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returned
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.Er ENOEXEC ) ,
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these functions will execute the shell with the path of
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the file as its first argument.
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(If this attempt fails, no further searching is done.)
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.Pp
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If the file is currently busy (the attempted
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.Xr execve 2
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returned
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.Er ETXTBUSY ) ,
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these functions will sleep for several seconds,
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periodically re-attempting to execute the file.
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.Pp
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The function
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.Fn exect
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executes a file with the program tracing facilities enabled (see
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.Xr ptrace 2 ) .
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.Sh RETURN VALUES
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If any of the
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.Nm exec
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functions returns, an error will have occurred.
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The return value is \-1, and the global variable
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.Va errno
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will be set to indicate the error.
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.Sh FILES
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.Bl -tag -width /bin/sh -compact
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.It Pa /bin/sh
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The shell.
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.El
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.Sh ERRORS
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.Fn execl ,
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.Fn execle ,
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.Fn execlp
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and
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.Fn execvp
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may fail and set
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.Va errno
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for any of the errors specified for the library functions
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.Xr execve 2
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and
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.Xr malloc 3 .
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.Pp
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.Fn exect
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and
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.Fn execv
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may fail and set
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.Va errno
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for any of the errors specified for the library function
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.Xr execve 2 .
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.Sh SEE ALSO
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.Xr sh 1 ,
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.Xr execve 2 ,
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.Xr fork 2 ,
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.Xr ptrace 2 ,
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.Xr environ 7
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.Sh COMPATIBILITY
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Historically, the default path for the
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.Fn execlp
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and
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.Fn execvp
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functions was
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.Dq Pa :/bin:/usr/bin .
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This was changed to improve security and behaviour.
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.Pp
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The behavior of
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.Fn execlp
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and
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.Fn execvp
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when errors occur while attempting to execute the file is historic
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practice, but has not traditionally been documented and is not specified
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by the
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.Tn POSIX
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standard.
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.Pp
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Traditionally, the functions
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.Fn execlp
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and
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.Fn execvp
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ignored all errors except for the ones described above and
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.Er ENOMEM
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and
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.Er E2BIG ,
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upon which they returned.
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They now return if any error other than the ones described above occurs.
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.Sh STANDARDS
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.Fn execl ,
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.Fn execv ,
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.Fn execle ,
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.Fn execlp
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and
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.Fn execvp
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conform to
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.St -p1003.1-90 .
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