execle(3C) — UTek 4319-3.0



EXECL(3C)               COMMAND REFERENCE               EXECL(3C)



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

SYNOPSIS
     execl(filename, arg0, arg1, ..., argn, 0)
     char *filename, *arg0, *arg1, ..., *argn;

     execlp(filename, arg0, arg1, ..., argn, 0)
     char *filename, *arg0, *arg1, ..., *argn;

     execv(filename, argv)
     char *filename, *argv[ ];

     execvp(filename, argv)
     char *filename, *argv[ ];

     execle(filename, arg0, arg1, ..., argn, 0, envp)
     char *filename, *arg0, *arg1, ..., *argn, *envp[ ];

     exect(filename, argv, envp)
     char *filename, *argv[ ], *envp[ ];

     extern char **environ;

DESCRIPTION
     These routines provide various interfaces to the execve
     system call.  Refer to execve(2) for a description of their
     properties; only brief descriptions are provided here.

     Exec in all its forms overlays the calling process with the
     named file, then transfers to the entry point of the core
     image of the file.  There can be no return from a successful
     exec; the calling core image is lost.

     The filename argument is a pointer to the name of the file
     to be executed.  The pointers arg[0], arg[1] ...  address
     null-terminated strings.  Conventionally arg[0] is the name
     of the file.

     Two interfaces are available.  Execl is useful when a known
     file with known arguments is being called.  The arguments to
     execl are the character strings constituting the file and
     the arguments; the first argument is conventionally the same
     as the filename (or its last component).  A 0 argument must
     end the argument list.  Execle is like execl but uses the
     addition argument envp; see below.

     The execv version is useful when the number of arguments is
     unknown in advance; the arguments to execv are the name of
     the file to be executed and a vector of strings containing
     the arguments.  The last argument string must be followed by



Printed 5/12/88                                                 1



EXECL(3C)               COMMAND REFERENCE               EXECL(3C)



     a ``0'' pointer.

     The exect version is used when the executed file is to be
     manipulated with ptrace(2). The program is forced to single
     step a single instruction giving the parent an opportunity
     to manipulate its state.  See ptrace(2).

     When a C program is executed, it is called as follows:

          main(argc, argv, envp)
          int argc;
          char **argv, **envp;

     where argc is the argument count and argv is an array of
     character pointers to the arguments themselves.  As
     indicated, argc is conventionally at least one and the first
     member of the array points to a string containing the name
     of the file.

     Argv is directly usable in another execv because argv[argc]
     is 0.

     Envp is a pointer to an array of strings that constitute the
     environment of the process.  Each string consists of a name,
     an equal sign (=), and a null-terminated value.  The array
     of pointers is terminated by a null pointer.  The shell
     sh(1sh) passes an environment entry for each global shell
     variable defined when the program is called.  See environ(7)
     for some conventionally used names.  The C run-time start-
     off routine places a copy of envp in the global cell
     environ, which is used by execv and execl to pass the
     environment to any subprograms executed by the current
     program.

     Execlp and execvp are called with the same arguments as
     execl and execv, but duplicate the shell's actions in
     searching for an executable file in a list of directories.
     The directory list is obtained from the environment.

     Even for the superuser, at least one of the execute-
     permission bits must be set for a file to be executed.

FILES
     /bin/sh        Shell, invoked if command file found by
                    execlp or execvp.

DIAGNOSTICS
     See execve(2).

RETURN VALUE
     If exec returns to the calling process, an error has
     occurred.  The return value will be -1.



Printed 5/12/88                                                 2



EXECL(3C)               COMMAND REFERENCE               EXECL(3C)



CAVEATS
     If execvp is called to execute a file that turns out to be a
     shell command file, and if it is impossible to execute the
     shell, the values of argv[0] and argv[-1] will be modified
     before return.

SEE ALSO
     csh(1csh), sh(1sh), execve(2), fork(2), ptrace(2), a.out(5),
     and environ(7).














































Printed 5/12/88                                                 3

%%index%%
na:288,139;
sy:427,4525;
de:4952,2000;7312,2451;
fi:9763,285;
di:10048,157;
rv:10205,266;
ca:10831,373;
se:11204,297;
%%index%%000000000151

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