************* BACK AND FORTH PAGING SUBROUTINE ************

PAGEFLOP

If they want to quit, do so

 If They want to quit subsession, Do SO!

  Decrement LOCAL and GLOBAL Page Counters

FORWARD

  Increment LOCAL and GLOBAL Page Counters

   *************** END PAGEFLOP *********************

P35

Shell Programming|Command Grouping|4-9.1|9,54

     Several commands may be grouped on the same 

line by separating the commands with a semicolons. 

For example:

ls; date; tbl *.doc | nroff | lpr

     Using a semicolon allows you to separate 

commands without typing them on subsequent lines.

P36

Shell Programming|Command Grouping|4-9.2|12,54

     A user may start a subshell, i.e., another level 

of command processing, by typing the command sh or csh,

or by grouping commands with ( and ).

( cd x_dir; rm junk; cc game.c; a.out )

The Subshell in the above example is alive until the 

last command in the parentheses is finished.

     NOTE: You must precede a <CR> with a backslash (\) 

to continue a long shell command onto a second line.

P37

Shell Programming|The Programming Environment|4-10.1|14,54

     Setting up one's programming environment is a 

process whereby one initializes one or more variables 

and makes them known to other subshells.

     Setting up the environment is most often done in 

your login command file:

              .profile   (under the Bourne Shell)

                .login   (under the C-Shell)

     Variables may be also be assigned values on 

a command line.

P38

Shell Programming|The Programming Environment|4-10.2|15,54

     The process of making variables available to 

other shells is a two-step process under the Bourne 

Shell.  It involves:

      1.  assigning a value to a variable and 

      2.  using the Bourne Shell command export with 

          the variable as the argument.  For example:

TERM=wy50; export TERM

     The above process is accomplished in a single 

step under the C Shell, by using the setenv command:

setenv  TERM  wy50

P39

Shell Programming|The Programming Environment|4-10.3|6,54

     You can see the value of all Shell variables

(i.e., your current programming environment) by using:

set  (under sh) or 

printenv (under csh).

P40

Shell Programming|The Programming Environment|4-10.4|12,54

     After you have logged on to a UNIX system, the

first program that the login process invokes is your

shell program, usually sh or csh.  This program initially 

executes the commands in the system-wide login command file.

     The system-wide login command file for sh is 

/etc/profile; for csh it is /etc/cshrc.

     These files are accessible to the system administrator 

and should contain parameters with system-wide effects.

P41

Shell Programming|The Programming Environment|4-10.5|5,54

     Following the execution of the commands in 

/etc/profile or in /etc/cshrc, the Shell goes into

your home directory, and executes your private login 

command file (.profile under sh or .login under csh), 

thereby setting up your personal environment.

P42

Shell Programming|The Programming Environment|4-10.6|14,53

    The contents of a typical .profile file may be 

as shown below:

        % cat .profile

        HOME=/usr/home/deutsch

        SHELL=/bin/csh

        MAIL=$HOME/mailfile

        PATH=:/usr/nelson/bin:/usr/ucb:/bin:/usr/bin

        TERM=vt100

        USER=deutsch

        export HOME PATH MAIL TERM

        date

        echo "NUMBER OF USERS `who | wc -l`"

P43

Shell Programming| More Shell Scripts|4-11.1|10,60

TASK:  Assume a file called address contains your 

company address and you want to print 1000 shipping labels.

We'll show you an example of a Bourne Shell script and 

a C Shell script to accomplish the task.  Both examples 

will use the "while" loop, with a FALSE condition being

reached when the "while" statement evaluates to zero.

Note the use of the command expr which is used to

evaluate arithmetic expressions.

P44

Shell Programming| More Shell Scripts|4-11.2|16,40

-------- example of sh script -------- 

         count=1000

         while test $count -ne 0

         do

             cat address

             count=`expr $count - 1`

         done

---------------------------------------

-------- example of csh script -------- 

         set count=1000

         while ($count)

             cat address

             set count=`expr $count - 1`

         end

----------------------------------------

P45

Shell Programming| More Shell Scripts|4-11.3|11,54

TASK:  Write a "cleanup" script under the Bourne Shell 

that will look recursively through all of a user's 

directories, starting at the current one, and search 

for executable and object files.  Ask whether the user 

wants to delete the file.  Have a positive response 

remove the file.

NOTE: the line if test "$i" = ".o -o -x $i tests 

whether the file $i is either an object or an executable 

file.  if test "$response" = y tests whether the value 

of the string "response" equals "y".

P46

Shell Programming| More Shell Scripts|4-11.4|15,54

               Bourne Shell cleanup script

     -----------------------------------------------

     for i in *

     do

         if test -d $i

         then (cd $i; $HOME/cleanup;)

         else if test "$i" = *.o -o -x $i

              then echo "you want to delete file $i"

                  read response

                  if test "$response" = y

                  then rm $i

                  fi

              fi

         fi

     done