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BSD 2.11 - man page for execlp (bsd section 3)

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EXECL(3)										 EXECL(3)

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

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

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

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

       exect(name, argv, envp)
       char *name, *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 name 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 file name (or its last
       component).  A 0 argument must end the argument list.

       The  execv version is useful when the number of arguments is unknown in advance; the argu-
       ments 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 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.  On the VAX-11 this is done by setting the trace bit in the process
       status longword.  Exect is not available on the PDP-11.

       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  argu-
       ments  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 "=", and a null-terminated value.  The array of point-
       ers is terminated by a null pointer.  The shell sh(1) passes an environment entry for each
       global shell variable defined when the program is called.  See environ(7) for some conven-
       tionally 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 direc-
       tory list is obtained from the environment.

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

SEE ALSO
       execve(2), fork(2), environ(7), csh(1)

DIAGNOSTICS
       If the file cannot be found, if it is not executable, if it does not start  with  a  valid
       magic  number  (see  a.out(5)), if maximum memory is exceeded, or if the arguments require
       too much space, a return constitutes the diagnostic; the return value is -1.  Even for the
       super-user,  at least one of the execute-permission bits must be set for a file to be exe-
       cuted.

BUGS
       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.

4.2 Berkeley Distribution		  August 4, 1987				 EXECL(3)
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