execv
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NAME
execl, execlp, execle, exect, execv, execvp - 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 exect( const char *path, char *const argv[]);
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 exect, 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 begin executed. The array of
pointers must be terminated by a NULL pointer.
The execle and exect functions also specify the environ-
ment 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 environ-
ment 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 (/) charac-
ter. The search path is the path specified in the envi-
ronment by the PATH variable. If this variable isn't
specified, the default path ``/bin:/usr/bin:'' is used (is
this true for Linux?). 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.)
If the file is currently busy (the attempted execve
returned ETXTBUSY), these functions will sleep for several
seconds, periodically re-attempting to execute the file.
(Is this true for Linux?)
The function exect executes a file with the program trac-
ing facilities enabled (see ptrace(2).
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
/bin/sh
ERRORS
Execl, execle, execlp and execvp may fail and set errno
for any of the errors specified for the library functions
execve(2) and malloc(3).
Exect and execv may fail and set errno for any of the
errors specified for the library function execve(2).
SEE ALSO
sh(1), execve(2), fork(2), trace(2), environ(7), ptrace(2)
COMPATIBILITY
Historically, the default path for the execlp and execvp
functions was ``:/bin:/usr/bin''. This was changed to
place the current directory last to enhance system secu-
rity.
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.
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'').
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Copyright (C) 1998
Hurricane Electric.
All Rights Reserved.