exec(3) - NetBSD Manual Pages

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EXEC(3)                   NetBSD Programmer's 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 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 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 speci-
     fied in the environment by ``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(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(3) functions returns, an error will have occurred.
     The return value is -1, and the global variable errno will be set to in-
     dicate 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)


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 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 IEEE
     Std1003.1-1990 (``POSIX'').

NetBSD 1.4                     January 24, 1994                              2