EXEC (3)
execute a file
SYNOPSIS
#include <unistd.h>
extern char **environ;
int execl( const char * path , const char * arg , ...);
int execlp( const char * file , const char * arg , ...);
int execle( const char * path , const char * arg
, ..., char * const envp []);
int execv( const char * path , char *const argv []);
int execvp( const char * file , char *const argv []);
DESCRIPTION
The
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
execve (2).
(See the manual page for
execve
for detailed information about the replacement of the current process.)
The initial argument for these functions is the pathname of a file which is
to be executed.
The
const char *arg
and subsequent ellipses in the
execl ,
execlp ,
and
execle
functions can be thought of as
arg0 ,
arg1 ,
...,
argn .
Together they describe a list of one or more pointers to null-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
must
be terminated by a
NULL
pointer.
The
execv
and
execvp
functions provide an array of pointers to null-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
must
be terminated by a
NULL
pointer.
The
execle
function also specifies the environment of the executed process by following
the
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 null-terminated strings and
must
be terminated by a
NULL
pointer. The other functions take the environment for the new process
image from the external variable
environ
in the current process.
Some of these functions have special semantics.
The functions
execlp
and
execvp
will duplicate the actions of the shell in searching for an executable file
if the specified file name does not contain a slash (/) character. The
search path is the path specified in the environment by the
PATH
variable. If this variable isn't specified, the default path
``:/bin:/usr/bin'' is used. In addition, certain
errors are treated specially.
If permission is denied for a file (the attempted
execve
returned
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
errno
set to
EACCES .
If the header of a file isn't recognized (the attempted
execve
returned
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.)
RETURN VALUES
If any of the
exec
functions returns, an error will have occurred. The return value is -1,
and the global variable
errno
will be set to indicate the error.
FILES
ERRORS
All of these functions may fail and set
errno
for any of the errors specified for the library function
execve (2).
SEE ALSO
COMPATIBILITY
On some other systems the default PATH has the current working
directory listed after
/bin
and
/usr/bin ,
as an anti-Trojan-horse measure. As of libc 5.4.7, Linux still uses the
traditional "current directory first" default PATH.
The behavior of
execlp
and
execvp
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. BSD (and possibly other systems) do an automatic
sleep and retry if ETXTBSY is encountered. Linux treats it as a hard
error and returns immediately.
Traditionally, the functions
execlp
and
execvp
ignored all errors except for the ones described above and
ENOMEM
and
E2BIG ,
upon which they returned. They now return if any error other than the ones
described above occurs.
STANDARDS
Execl ,
execv ,
execle ,
execlp
and
execvp
conform to
IEEE Std1003.1-88 (``POSIX.1'').
man3/exec.3
man3/exec.3
man3/exec.3
man3/exec.3
man3/exec.3
man3/exec.3
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