322 lines
8.0 KiB
Groff
322 lines
8.0 KiB
Groff
.\" 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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.\" 4. 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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.\" $FreeBSD$
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.\"
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.Dd January 24, 1994
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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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.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" ... /* "(char *)0" */
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.Ft int
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.Fn execlp "const char *file" "const char *arg" ... /* "(char *)0" */
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.Ft int
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.Fo execle
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.Fa "const char *path" "const char *arg" ...
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.Fa /*
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.Bk -words
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.Fa "(char *)0" "char *const envp[]" */
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.Ek
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.Fc
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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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.Ft int
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.Fn execvP "const char *file" "const char *search_path" "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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.Fn execvp ,
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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 argument list
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or the pointer to the argv array with an additional argument.
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This additional argument 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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.Fn execvp ,
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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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For
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.Fn execlp
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and
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.Fn execvp ,
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search path is the path specified in the environment by
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.Dq Ev PATH
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variable.
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If this variable is not specified,
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the default path is set according to the
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.Dv _PATH_DEFPATH
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definition in
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.In paths.h ,
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which is set to
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.Dq Ev /usr/bin:/bin .
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For
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.Fn execvP ,
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the search path is specified as an argument to the function.
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In addition, certain errors are treated specially.
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.Pp
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If an error is ambiguous (for simplicity, we shall consider all
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errors except
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.Er ENOEXEC
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as being ambiguous here, although only the critical error
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.Er EACCES
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is really ambiguous),
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then these functions will act as if they stat the file to determine
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whether the file exists and has suitable execute permissions.
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If it does, they will return immediately with the global variable
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.Va errno
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restored to the value set by
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.Fn execve .
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Otherwise, the search will be continued.
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If the search completes without performing a successful
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.Fn execve
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or terminating due to an error,
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these functions 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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or
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.Er ENOENT
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according to whether at least one file with suitable execute permissions
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was found.
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.Pp
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If the header of a file is not recognized (the attempted
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.Fn execve
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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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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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.Fn 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 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 place the current directory last to enhance system
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security.
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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 not quite historic
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practice, and 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 ETXTBSY ,
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upon which they retried after sleeping for several seconds, 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 for
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.Er ETXTBSY ,
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and determine existence and executability more carefully.
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In particular,
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.Er EACCES
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for inaccessible directories in the path prefix is no longer
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confused with
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.Er EACCES
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for files with unsuitable execute permissions.
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In
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.Bx 4.4 ,
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they returned upon all errors except
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.Er EACCES ,
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.Er ENOENT ,
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.Er ENOEXEC
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and
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.Er ETXTBSY .
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This was inferior to the traditional error handling,
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since it breaks the ignoring of errors for path prefixes
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and only improves the handling of the unusual ambiguous error
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.Er EFAULT
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and the unusual error
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.Er EIO .
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The behaviour was changed to match the behaviour of
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.Xr sh 1 .
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.Sh ERRORS
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The
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.Fn execl ,
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.Fn execle ,
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.Fn execlp ,
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.Fn execvp
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and
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.Fn execvP
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functions
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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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The
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.Fn exect
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and
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.Fn execv
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functions
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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 ktrace 2 ,
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.Xr ptrace 2 ,
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.Xr environ 7
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.Sh STANDARDS
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The
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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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functions
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conform to
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.St -p1003.1-88 .
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The
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.Fn execvP
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function first appeared in
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.Fx 5.2 .
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