Mega CD-ROM 1/megacd_rom_1.zip/megacd_rom_1/VIRUS/AM40.ZIP/PATHINFO.TXT

Text File | 1989-02-16 | 6KB | 96 lines

             INFORMATION ON THE DOS ENVIRONMENT PATH STRING
             ----------------------------------------------

          All versions of PC and MS DOS above 2.0 maintain an area in
     memory called the environment.  The environment contains a series of
     text strings that are used by DOS and applications programs for
     various purposes.  You can see what strings are currently in the
     enviroment by typing SET and pressing <RETURN> from the DOS level.  As
     a minimum, the environment will contain the string COMSPEC= followed
     by a DOS directory path and (usually) COMMAND.COM.  Most hard disk
     equipped machines will show the following COMSPEC string:

                         COMSPEC=C:\COMMAND.COM

          Other strings that frequently appear in the environment are the
     PROMPT= and PATH= strings.  Control of the environment is effected
     through the DOS SET command, which may be entered at the DOS level or
     from a batch (like AUTOEXEC.BAT) file.  For example, if a user desired
     that DOS used a copy of COMMAND.COM that was in a directory named
     C:\DOS, he/she might place the command SET COMSPEC=C:\DOS\COMMAND.COM
     in the AUTOEXEC.BAT file.  After booting, DOS would load COMMAND.COM
     from C:\DOS each time it needed to reload the command interpreter.
     All other copies of COMMAND.COM in the system would be superfluous and
     ignored by DOS.
          One very useful string that can be placed in the DOS environment
     by the user is the PATH= string.  When the name of an executable file
     is issued from the DOS level, DOS will first look in the current
     subdirectory for the file.  If it finds it, it loads and executes it
     and all is fine.  If it cannot find the file in the current directory,
     DOS will search the environment for the PATH= designator.  If one
     exists, DOS will start searching the system directories that are in the
     PATH= string for the executable file.  For example, suppose that
     the AUTOEXEC.BAT contains the command SET PATH=C:\DOS;D:\UTIL;E:\JUNK.
     Note that directory path names are separated by semicolons and can
     (and should) include the drive designator.  Now further suppose that
     the user is in a directory named D:\SOMENAME and desires to run the
     program MYPROG.EXE but MYPROG.EXE is not resident in D:\SOMENAME.
     When the user enters MYPROG, DOS, unable find it in the current
     directory, starts searching the directories in the PATH= string
     starting with C:\DOS.  If MYPROG.EXE was in D:\UTIL, DOS would load
     and execute the program and D:\UTIL would be the active directory when
     the program received control from DOS.  Obviously, if DOS cannot find
     MYPROG.EXE in any of directories in the PATH= string, the message BAD
     COMMAND OR FILENAME will be displayed.
          The exact same sequence is followed if a running program calls
     DOS to execute a program but with one possible important difference.
     For technical reasons, some programs (like ArcMaster) need to load a
     secondary copy of COMMAND.COM and then pass the name of the program to
     be executed to COMMAND.COM.  This is accomplished by searching the
     environment string for the COMSPEC= string to locate COMMAND.COM,
     changing to that directory, and telling DOS to load COMMAND.COM.  The
     command passed to DOS might look somethin like this:

                           COMMAND.COM MYPROG.EXE

     This tells DOS to run COMMAND.COM and for COMMAND.COM to load and
     execute MYPROG.EXE.  Even if MYPROG.EXE were located in the active
     directory when the applications program passed this command to DOS,
     COMMAND.COM might not find MYPROG.EXE because the applications program
     swithed to the directory where COMMAND.COM was located in order to
     start things rolling.  Therefore, unless MYPROG.EXE was in a directory
     contained in the PATH= string or in the same directory as COMMAND.COM,
     DOS would not find it.

          ArcMaster depends upon the presence of an archive system's
     executable files (PAK.EXE, ARC.EXE, PKZIP.EXE, etc.). It calls these
     programs by using the command sequence just described and therefore
     cannot function properly unless these programs are in a directory
     specified in the PATH= string.  The simplest thing to do is to place
     your archive system files and LIST.COM in one subdirectory and place
     its DOS path name in the environment.  For example, suppose you are
     using PKWare and you place PKZIP, PKUNXIP, and LIST in a directory
     named C:\ARCUTILS.  Placing the following line in your AUTOEXEC.BAT
     file and rebooting will ensure that ArcMaster will function properly:

                             PATH=C:\ARCUTILS

     Obviously, the PATH= string can contain other directory path names and
     you may already have a PATH= command in your AUTOEXEC.BAT file.  If
     so, just add the directory containing the archive system files to the
     string.  For maximum speed, make it the first directory name in the
     string.
          When ArcMaster loads it will check your system environment
     to see if a PATH= string exists.  If so, it will search each
     directory in the string to see if any of the five supported archive
     system files can be found in the directories defined in the PATH.
     If not, or if no path string exists, ArcMaster will display a message
     to that effect and pause. If this occurs, take the steps described
     above and rerun Arcmaster.

     NOTE:  It is **important** that DOS 2.x users use CAPS when entering
            path commands into the environment.  DOS 3.x automatically
            changes all characters to upper case but DOS 2.x does not.