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EXEC(3)			 BSD Library Functions Manual		       EXEC(3)

NAME
     execl, execlp, execle, exect, execv, execvp -- execute a file

LIBRARY
     Standard C	Library	(libc, -lc)

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[], 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(2) for detailed information	about the replacement of the current
     process.  The script(7) manual page provides detailed information about
     the execution of interpreter scripts.)

     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	being executed.	 The array of pointers
     must be terminated	by a NULL pointer.

     The execle() and exect() functions	also specify 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	point-
     ers 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 speci-
     fied, _PATH_DEFPATH from <paths.h>	is used	instead, its value being:
     /usr/bin:/bin:/usr/pkg/bin:/usr/local/bin.	 In addition, certain errors
     are treated specially.

     If	permission is denied for a file	(the attempted execve(2) 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(2) re-
     turned 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(2) returned
     ETXTBUSY),	these functions	will sleep for several seconds,	periodically
     re-attempting to execute the file.

     The function exect() executes a file with the program tracing 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  The shell.

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 speci-
     fied for the library function execve(2).

SEE ALSO
     sh(1), execve(2), fork(2),	ptrace(2), environ(7), script(7)

COMPATIBILITY
     Historically, the default path for	the execlp() and execvp() functions
     was ":/bin:/usr/bin".  This was changed to	improve	security and behav-
     iour.

     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 ex-
     cept 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 ISO/IEC
     9945-1:1990 ("POSIX.1").

BSD				  May 6, 2005				   BSD

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | FILES | ERRORS | SEE ALSO | COMPATIBILITY | STANDARDS

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