UNIX for Dummies Questions & Answers

#! /usr/bin/ksh
#
#  scroller ---  display text, but sleep every few lines.
#
#
#  scroller will copy 5 lines from standard input to the 
#  local terminal and then sleep for one second.  
#
#  You  can override the 5 lines with a "-l n" option.  
#  And you use  a "-s n" to override the sleep time.
#
#  You can type your interrupt character (often control c)
#  to get a menu that will let you adjust these values.
#
#  You can use -m to go straight to the menu at startup
#  
#  You can specify filenames or scroller can just read from 
#  standard in.
#
USAGE="usage: scroller [-s n] [-l n] [-m] [filename1] [filename2] ..."
  
#
#  initialize variables
#
#  Set reasonable initial values here.  TASK controls the main 
#  loop as described below.  snooze is the number of seconds for
#  the sleep.  lpp (lines per page) is the number of lines to
#  dispaly before sleeping.  lines will repeatedly cycle from 0
#  to npp as the program runs.  totallines is a count of lines
#  processed so far.  And we turn off IFS so the reads work with
#  data that has leading white space.
  
TASK=2
snooze=1
lpp=5
lines=0
totallines=0
IFS=""

#
#  Now Process the command line
#

error=0
while getopts :s:l:m  o ; do
        case $o in
        s)      if [[ $OPTARG -gt 0 && $OPTARG -lt 100 ]] ; then
                        snooze=$OPTARG
                else
                        print $OPTARG is illegal
                        error=1
                fi
                ;;
        l)      if [[ $OPTARG -gt 0 && $OPTARG -lt 100 ]] ; then
                        lpp=$OPTARG
                else
                        print $OPTARG is illegal
                        error=1
                fi
                ;;
        m)      TASK=2
                ;;
        ?)      print error argument $OPTARG is illegal
                error=1
                ;;
        esac
done
shift OPTIND-1
if ((error)) ; then
        print $USAGE
        TASK=0
fi


#
#  Open first file or indicate that we are using stdin
#

if (($# >= 1)) ; then
        input=$1
        exec < $input
        shift
else
        input="(standard input)"
fi


#
#  Major loop.  TASK can be 0 or 1 or 2.  If TASK is set we 
#  loop doing either task 1 or task 2.  Either task can switch 
#  to the other.  And both tasks can abort by setting TASK=0.  
#  But control c will switch to task 1.
#

trap interrupt=1 2
interrupt=0
while ((TASK)) ; do
        if ((interrupt)) ; then
                interrupt=0
                TASK=1
        fi
        case $TASK in

#
#   Task 1 --- display service menu
#

        1)      print  
                print  '=====[[ scroller service menu ]]====='
                print
                print  "      $totallines lines processed so far from $input"
                print  "      sleep seconds = $snooze"
                print  "      lines per page = $lpp"
                print  
                print  '   1) list the text'
                print  '   2) set lines per page'
                print  '   3) set sleep seconds'
                print  '   4) abort'
                print
                print -n  "[Enter Selection]====>>"
                read < /dev/tty
                case $REPLY in 
                1)      TASK=2
                        ;;
                2)      print lines per page is currently $lpp
                        print -n enter new value --
                        read val < /dev/tty
                        if [[ $val -gt 0 && $val -lt 100 ]] ; then
                                lpp=$val
                        else
                                print $val is illegal
                        fi
                        ;;
                3)      print sleep seconds is currently $snooze
                        print -n  enter new value --
                        read val < /dev/tty
                        if [[ $val -gt 0 && $val -lt 100 ]] ; then
                                snooze=$val
                        else
                                print $val is illegal
                        fi
                        ;;
                4)      TASK=0
                        ;;
                *)      print illegal response
                        print REPLY = $REPLY
                        ;;
                esac
                ;;

#
#  Task 2 --- copy lines from stdin to stdout
#
#    Read a line, increment counts, sleep if it's time
#

        2)      if read line ; then
                        print -r -- "$line"
                        ((totallines=totallines+1))
                        ((lines=lines+1))
                        if ((lines >= lpp)) ; then
                                lines=0
                                sleep $snooze
                        fi
                else
#
#    No more input.  Open a new file or give up.
#

                        if [[ $# -ge 1 ]] ; then
                                input=$1
                                exec < $input
                                shift
                        else
                                TASK=0
                        fi
                fi
                ;;

#
#   Task * --- can't happen
#
        *)      print -u2 $0: impossible error TASK = $TASK
                TASK=0
                ;;
        esac
done

((totallines)) && print "$totallines" total lines processed

exit 0

#ifdef __STDC__
#define PROTOTYPICAL
#endif
#ifdef __cplusplus
#define PROTOTYPICAL
#endif

#include <stdlib.h>
#include <sys/time.h>

#ifdef PROTOTYPICAL
int main(int argc, char *argv[])
#else
main(argc,argv)
char *argv[];
#endif

{
        int millisecs, microsecs;
        struct timeval tv;

        millisecs=atoi(argv[1]);
        microsecs=millisecs*1000;

        tv.tv_sec=microsecs/1000000;
        tv.tv_usec=microsecs%1000000;

        select(0, NULL, NULL, NULL, &tv);
        exit(0);
}