*command
**
Form:           IF  "NOT/S,WARN/S,ERROR/S,FAIL/S,EQ/K,,EXISTS/K,MCTYPE/K*
                    *SYSTYPE/K,MCNAME/K"
Purpose:        To allow conditionals within command sequences.
Author:         ARA
Specification:
   If one or more of the specified conditions is satisfied, then the
rest of the command line (after ';') is obeyed;  otherwise it is
skipped and the return code preserved.
        NOT            reverses the result
        WARN           satisfied if previous return code >= 5
        ERROR              "      "     "       "     "  >= 10
        FAIL               "      "     "       "     "  >= 20
        EQ a b         satisfied if a and b are textually
                       identical (disregarding case).
        EXISTS file    satisfied if the file exists (i.e. can
                       be opened for input).
        MCTYPE string  satisfied if string matches the machine type
                       string held in the rootnode info vector.
                       (e.g. PDP11, NOVA, LSI4, 68000)
        SYSTYPE string satisfied if string matches the system type string.
                       (e.g. S-TRIPOS, FM-TRIPOS)
        MCNAME string  satisfied if string matches the machine name.
                       (e.g. ALPHA, GOLD)
    Note that the FAILAT command must be used in order to ensure that
conditions that would otherwise abort a command sequence can be tested
using WARN and FAIL.  Use HELP FAILAT COMMAND and HELP COMMAND RC for further
information.

Examples:
        IF EXISTS file; TYPE file
        IF NOT WARN; SKIP no-warning-label
        IF ERROR; QUIT 10
        IF MCTYPE 68000; 68000-OBJ.MYPROG
        IF NOT EQ <arg$val> val; ECHO "<arg$val> not equal to 'val'"
             {this last example is typical of a line in a C command
              sequence}


