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\"     @(#)exec.3       8.3 (Berkeley) 1/24/94
\"
Dd September 1, 2019
Dt EXEC 3
Os
Sh NAME
Nm execl ,
Nm execlp ,
Nm execlpe ,
Nm execle ,
Nm exect ,
Nm execv ,
Nm execvp ,
Nm execvpe
Nd execute a file
Sh LIBRARY
Lb libc
Sh SYNOPSIS
In unistd.h
Vt extern char **environ;
Ft int
Fn execl "const char *path" "const char *arg" ...
Ft int
Fn execlp "const char *file" "const char *arg" ...
Ft int
Fn execlpe "const char *file" "const char *arg" ... "char *const envp[]"
Ft int
Fn execle "const char *path" "const char *arg" ... "char *const envp[]"
Ft int
Fn exect "const char *path" "char *const argv[]"  "char *const envp[]"
Ft int
Fn execv "const char *path" "char *const argv[]"
Ft int
Fn execvp "const char *file" "char *const argv[]"
Ft int
Fn execvpe "const char *file" "char *const argv[]" "char *const envp[]"
Sh DESCRIPTION
The
Fn exec
family of functions replaces the current process image with a
new process image.
The functions described in this manual page are front-ends for the function
Xr execve 2 .
(See the manual page for
Xr execve 2
for detailed information about the replacement of the current process.
The
Xr script 7
manual page provides detailed information about the execution of
interpreter scripts.)
Pp
The initial argument for these functions is the pathname of a file which
is to be executed.
Pp
The
Fa "const char *arg"
and subsequent ellipses in the
Fn execl ,
Fn execlp ,
Fn execlpe ,
and
Fn execle
functions can be thought of as
Em arg0 ,
Em arg1 ,
\&...,
Em argn .
Together they describe a list of one or more pointers to NUL-terminated
strings that represent the argument list available to the executed program.
The first argument, by convention, should point to the file name associated
with the file being executed.
The list of arguments
Em must
be terminated by a
Dv NULL
pointer.
Pp
The
Fn exect ,
Fn execv ,
Fn execvp ,
and
Fn execvpe
functions provide an array of pointers to NUL-terminated strings that
represent the argument list available to the new program.
The first argument, by convention, should point to the file name associated
with the file being executed.
The array of pointers
Sy must
be terminated by a
Dv NULL
pointer.
Pp
The
Fn execle ,
Fn execlpe ,
Fn exect ,
and
Fn execvpe
functions also specify the environment of the executed process by following
the
Dv NULL
pointer that terminates the list of arguments in the parameter list
or the pointer to the argv array with an additional parameter.
This additional parameter is an array of pointers to NUL-terminated strings
and
Em must
be terminated by a
Dv NULL
pointer.
The other functions take the environment for the new process image from the
external variable
Va environ
in the current process.
Pp
Some of these functions have special semantics.
Pp
The functions
Fn execlp ,
Fn execlpe ,
Fn execvp ,
and
Fn execvpe
will duplicate the actions of the shell in searching for an executable file
if the specified file name does not contain a slash
Dq Li \&/
character.
The search path is the path specified in the environment by the
Ev PATH
variable.
If this variable isn't specified,
Va _PATH_DEFPATH
from
In paths.h
is used instead, its value being:
Pa /usr/bin:/bin:/usr/pkg/bin:/usr/local/bin .
In addition, certain errors are treated specially.
Pp
If permission is denied for a file (the attempted
Xr execve 2
returned
Er EACCES ) ,
these functions will continue searching the rest of
the search path.
If no other file is found, however, they will return with the global variable
Va errno
set to
Er EACCES .
Pp
If the header of a file isn't recognized (the attempted
Xr execve 2
returned
Er ENOEXEC ) ,
these functions will execute the shell with the path of
the file as its first argument.
(If this attempt fails, no further searching is done.)
Pp
If the file is currently busy (the attempted
Xr execve 2
returned
Er ETXTBUSY ) ,
these functions will sleep for several seconds,
periodically re-attempting to execute the file.
Pp
The function
Fn exect
executes a file with the program tracing facilities enabled (see
Xr ptrace 2 ) .
Sh RETURN VALUES
If any of the
Fn exec
functions returns, an error will have occurred.
The return value is \-1, and the global variable
Va errno
will be set to indicate the error.
Sh FILES
Bl -tag -width /bin/sh -compact
It Pa /bin/sh
The shell.
El
Sh COMPATIBILITY
Historically, the default path for the
Fn execlp
Fn execlpe ,
Fn execvp ,
and
Fn execvpe
functions was
Dq Pa :/bin:/usr/bin .
This was changed to improve security and behaviour.
Pp
The behavior of
Fn execlp ,
Fn execlpe ,
Fn execvp ,
and
Fn execvpe
when errors occur while attempting to execute the file is historic
practice, but has not traditionally been documented and is not specified
by the POSIX standard.
Pp
Traditionally, the functions
Fn execlp ,
Fn execlpe ,
Fn execvp ,
and
Fn execvpe
ignored all errors except for the ones described above and
Er ENOMEM
and
Er E2BIG ,
upon which they returned.
They now return if any error other than the ones described above occurs.
Sh ERRORS
Fn execl ,
Fn execle ,
Fn execlp ,
Fn execlpe ,
Fn execvp ,
and
Fn execvpe
may fail and set
Va errno
for any of the errors specified for the library functions
Xr execve 2
and
Xr malloc 3 .
Pp
Fn exect
and
Fn execv
may fail and set
Va errno
for any of the errors specified for the library function
Xr execve 2 .
Sh SEE ALSO
Xr sh 1 ,
Xr execve 2 ,
Xr fork 2 ,
Xr ptrace 2 ,
Xr environ 7 ,
Xr script 7
Sh STANDARDS
Fn execl ,
Fn execv ,
Fn execle ,
Fn execlp ,
and
Fn execvp
conform to
St -p1003.1-90 .
Sh HISTORY
The
Fn exec
function appeared in
At v1 .
The
Fn execlpe
function appeared first in QNX and the
Fn execvpe
function exists on both
Nx
and QNX.

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