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 avail-
     able 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 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, _PATH_DEFPATH from <paths.h> is used instead, its value being: /usr/bin:/bin:/usr/pkg/bin:/usr/local/bin.  In addition, cer-
     tain 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) 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(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 specified 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 be-
     haviour.

     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 ISO/IEC 9945-1:1990 (``POSIX.1'').

BSD
								    May 6, 2005 							       BSD