MirOS Manual: exec(3), execl(3), execle(3), execlp(3), execv(3), execvp(3)

EXEC(3)                    BSD Programmer's Manual                     EXEC(3)

NAME

     execl, execlp, execle, 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
     execv(const char *path, char *const argv[]);

     int
     execvp(const char *file, char *const argv[]);

DESCRIPTION

     The exec family of functions replace 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 NUL-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 execv() and execvp() functions provide an array of pointers to NUL-
     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 itself.

     The execle() function also specifies the environment of the executed pro-
     cess 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 NUL-
     terminated strings and must be terminated by a null pointer itself. 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 speci-
     fied, _PATH_DEFPATH from <paths.h> is used instead, its value being:
     /usr/bin:/bin:/usr/sbin:/sbin:/usr/X11R6/bin:/usr/local/bin

     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 glo-
     bal 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.)

RETURN VALUES

     If any of the exec functions return, an error has occurred. The return
     value is -1, and the global variable errno will be set to indicate the
     error.

FILES

     /bin/sh  default shell program

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).

     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), ktrace(2), ptrace(2), environ(7)

STANDARDS

     Historically, the default path for the execlp() and execvp() functions
     was .:/bin:/usr/bin. This was changed to improve security and behaviour.

     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.

     execl(), execv(), execle(), execlp() and execvp() conform to IEEE Std
     1003.1-1988 ("POSIX").

MirOS BSD #10-current          January 24, 1994                              1

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