FreeBSD Man Pages

exec(3)

NAME

     execl, execlp, execle, exect, execv, execvp, 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, ... /*, (char *)0 */);

     int
     execlp(const char *file, const char *arg, ... /*, (char *)0 */);

     int
     execle(const char *path, const char *arg, ...
	 /*, (char *)0, 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[]);

     int
     execvP(const char *file, const char *search_path, 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 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(), execvp(), 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.

     Some of these functions have special semantics.

     The functions execlp(), execvp(), 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.  For execlp() and
     execvp(), search path is the path specified in the environment by
     ``PATH'' variable.  If this variable isn't specified, the default path is
     set according to the _PATH_DEFPATH definition in <paths.h>, which is set
     to ``/usr/bin:/bin''.  For execvP(), the search path is specified as an
     argument to the function.	In addition, certain errors are treated spe-
     cially.

     If an error is ambiguous (for simplicity, we shall consider all errors
     except ENOEXEC as being ambiguous here, although only the critical error
     EACCES is really ambiguous), then these functions will act as if they
     stat the file to determine whether the file exists and has suitable exe-
     cute permissions.	If it does, they will return immediately with the
     global variable errno restored to the value set by execve().  Otherwise,
     the search will be continued.  If the search completes without performing
     a successful execve() or terminating due to an error, these functions
     will return with the global variable errno set to EACCES or ENOENT
     according to whether at least one file with suitable execute permissions
     was found.

     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.)

     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

     The execl(), execle(), execlp(), execvp() and execvP() functions may fail
     and set errno for any of the errors specified for the library functions
     execve(2) and malloc(3).

     The exect() and execv() functions 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), ktrace(2), ptrace(2), environ(7)

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 security.

     The behavior of execlp() and execvp() when errors occur while attempting
     to execute the file is not quite historic practice, and has not tradi-
     with unsuitable execute permissions.  In 4.4BSD, they returned upon all
     errors except EACCES, ENOENT, ENOEXEC and ETXTBSY.  This was inferior to
     the traditional error handling, since it breaks the ignoring of errors
     for path prefixes and only improves the handling of the unusual ambiguous
     error EFAULT and the unusual error EIO.  The behaviour was changed to
     match the behaviour of sh(1).

STANDARDS

     The execl(), execv(), execle(), execlp() and execvp() functions conform
     to IEEE Std 1003.1-1988 (``POSIX.1'').  The execvP() function first
     appeared in FreeBSD 5.2.

FreeBSD 5.4		       January 24, 1994 		   FreeBSD 5.4

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