EXEC(3)                                                   EXEC(3)

     NAME
          exec, execl - execute a file

     SYNOPSIS
          #include <u.h>
          #include <libc.h>

          int exec(char *name, char* argv[])

          int execl(char *name, ...)

     DESCRIPTION
          Exec and execl overlay the calling process with the named
          file, then transfer to the entry point of the image of the
          file.

          Name points to the name of the file to be executed; it must
          not be a directory, and the permissions must allow the cur-
          rent user to execute it (see stat(3)). It should also be a
          valid binary image, as defined by the local operating sys-
          tem, or a shell script (see rc(1)). The first line of a
          shell script must begin with `#!'  followed by the name of
          the program to interpret the file and any initial arguments
          to that program, for example

               #!/bin/rc
               ls | mc

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

               void main(int argc, char *argv[])

          Argv is a copy of the array of argument pointers passed to
          exec; that array must end in a null pointer, and argc is the
          number of elements before the null pointer.  By convention,
          the first argument should be the name of the program to be
          executed.  Execl is like exec except that argv will be an
          array of the parameters that follow name in the call.  The
          last argument to execl must be a null pointer.

          For a file beginning #!, the arguments passed to the program
          (/bin/rc in the example above) will be the name of the file
          being executed, any arguments on the #! line, the name of
          the file again, and finally the second and subsequent argu-
          ments given to the original exec call.  The result honors
          the two conventions of a program accepting as argument a
          file to be interpreted and argv[0] naming the file being
          executed.

          Most attributes of the calling process are carried into the

     EXEC(3)                                                   EXEC(3)

          result; in particular, files remain open across exec (except
          those opened with OCEXEC OR'd into the open mode; see
          open(3)); and the working directory and environment (see
          getenv(3)) remain the same.  However, a newly exec'ed pro-
          cess has no notification handlers (see notify(3)).

     SOURCE
          /src/lib9/exec.c
          /src/lib9/execl.c

     SEE ALSO
          prof(1), intro(3), stat(3)

     DIAGNOSTICS
          If these functions fail, they return and set errstr. There
          can be no return from a successful exec or execl; the call-
          ing image is lost.

     BUGS
          On Unix, unlike on Plan 9, exec and execl use the user's
          current path to locate prog. This is a clumsy way to deal
          with Unix's lack of a union directory for /bin.

          To avoid name conflicts with the underlying system, exec and
          execl are preprocessor macros defined as p9exec and p9execl;
          see intro(3).