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EV_$INTRO                         Domain/OS                          EV_$INTRO


NAME
     intro - manipulating Domain/OS environment variables

SYNOPSIS (C)
     #include <apollo/base.h>
     #include <apollo/ev.h>

SYNOPSIS (Pascal)
     %include '/sys/ins/base.ins.pas';
     %include '/sys/ins/ev.ins.pas';

SYNOPSIS (FORTRAN)
     %include '/sys/ins/base.ins.ftn'
     %include '/sys/ins/ev.ins.ftn'

DESCRIPTION
     The ev_$ calls allow programs to manipulate variables in the process
     environment.  The process environment is part of the context associated
     with each process.  The process environment includes a list of name/value
     pairs called environment variables which are usually used to pass infor-
     mation from one program to another program running in the same process,
     or from a parent to a child process.

     Two common environment variables are USER and PATH; they are present in
     nearly all processes.  The USER variable is set by the system and identi-
     fies the owner of a process; it cannot be modified by descendant
     processes.  The PATH variable is also initially set by the system.  Its
     value is a list of directories to be searched for executable files; it
     can be modified by descendant processes to broaden or restrict the set of
     available programs.

     An environment variable is created by assigning a value to it.  It per-
     sists for the duration of the environment unless the variable is expli-
     citly deleted by the process running in the environment.  An environment
     variable can be accessed by its name, via ev_$get_var, or by its position
     in the environment variable list, via ev_$read_var_entry.

     The following is a list of the ev_$ calls.

                ev_$delete_var       delete an environment variable
                ev_$exist_var        test an environment variable
                ev_$get_var          get an environment variable
                ev_$read_var_entry   read an environment entry
                ev_$set_var          set an environment variable

   Constants
     ev_$string_max
          The maximum number of bytes in the name or value of an environment
          variable.

   Data Types
     ev_$string_ptr_t
          A pointer to type ev_$string_t, used to supply the names and values
          of environment variables to a program.

     ev_$string_t
          An array of up to ev_$string_max bytes, used to hold the name or
          value of an environment variable.