Korn shell script function to generate a calendar for a month and/or year. This script is an emulation of the Unix "cal" command.

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function usagemsg_cal_k93 {
  print "
Program: cal_k93

Generate a monthly or yearly calendar

Usage: ${1##*/} [-?vV] [[month] year]

  Where:
    -v = Verbose mode - displays cal_k93 function info
    -V = Very Verbose Mode - debug output displayed

Author: Dana French (dfrench@mtxia.com)
        Copyright 2006, All Rights Reserved

\"AutoContent\" enabled
"
}
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#### 
#### Description:
#### 
#### Function to generate a monthly or yearly calendar. 
#### Emulation of the Unix "cal" command.
#### 
#### Assumptions:
#### 
#### If specified, the year number is assumed to be greater
#### than 0.  If specified, the month number is assumed to be
#### between 1 and 12, 1=Jan 2=Feb 3=Mar...
#### 
#### Dependencies:
#### 
#### This function is dependent upon several other K93_Unix
#### functions to provide needed information, therefore these
#### functions must exist in a directory referenceced by the
#### FPATH variable.
#### 
#### Unfortunately, Korn shell does not provide a mechanism
#### to determine the current month and year.  So if no
#### command line arguments are provided to this function,
#### specifying the year and or month, the external Unix
#### command "date" is used to generate the current month and
#### year number.  If needed, the directory containing the
#### "date" command is assumed to be in the PATH.
#### 
#### Products:
#### 
#### This function can generate a monthly or yearly calendar
#### for any year greater than year number 0.
#### 
#### Configured Usage:
#### 
#### This function can be called from the command line or
#### from within other functions, and it can be called with
#### or without command line arguments.  If specified, the
#### command line arguments identify the year and month for
#### which to display a calendar.  See the usage message for
#### syntax. 
#### 
#### Details:
#### 
################################################################
function cal_k93 {
  typeset VERSION="1.0"
  typeset TRUE="1"
  typeset FALSE="0"
  typeset VERBOSE="${FALSE}"
  typeset VERYVERB="${FALSE}"
  typeset FULLYEAR="${FALSE}"
  typeset YEAR=$( date +"%Y" )
  typeset MONTH=$( date +"%m" )
  typeset SPACE="                            "
  typeset WID="21"
  DOW2=( Su  Mo  Tu  We  Th  Fr  Sa )
  DOW3=( Sun Mon Tue Wed Thu Fri Sat )
  DOWFULL=( Sunday Monday Tuesday Wednesday Thursday Friday Saturday )
  MNAME=( NUL January February March April May June July August September October November December )
  DIM=(   0  31  28  31  30  31  30  31  31  30  31  30  31 )

#### 
#### Process the command line options and arguments, saving
#### the values as appropriate.
#### 

  while getopts ":vV" OPTION
  do
      case "${OPTION}" in
          'v') VERBOSE="${TRUE}";;
          'V') VERYVERB="${TRUE}";;
        [?:#]) usagemsg_cal_k93 "${0}" && return 1 ;;
      esac
  done
   
  shift $(( ${OPTIND} - 1 ))
  
  trap "usagemsg_cal_k93 ${0}" EXIT

#### VIOLATION of the underlying principle behind the purpose
#### of K93_Unix.  Since Korn shell does not have a built-in
#### mechanism to determine the current month or the current
#### year, the external program "date" is used to determine
#### these values.

  (( ${#} == 1 )) && typeset YEAR="${1}"  FULLYEAR="${TRUE}"
  (( ${#} == 2 )) && typeset YEAR="${2}"  MONTH="${1}"

#### If more than two command line parameters remain, this is
#### an error.  Display an error message and return from the
#### function with a non-zero (2) exit code.

  if (( ${#} > 2 ))
  then
      print -u 2 -- "# Error: Invalid number of command line parameters"
      return 2
  fi

  trap "-" EXIT
  
#### 
#### Display some program info and the command line arguments specified
#### if "VERBOSE" mode was specified.
#### 

  (( VERYVERB == TRUE )) && set -x
  (( VERBOSE  == TRUE )) && print -u 2 -- "# Entering Function: ${0}"
  (( VERBOSE  == TRUE )) && print -u 2 -- "# Version..........: ${VERSION}"
  (( VERBOSE  == TRUE )) && print -u 2 -- "# Month Specified..: ${MONTH:-}"
  (( VERBOSE  == TRUE )) && print -u 2 -- "# Year Specified...: ${YEAR:-}"

################################################################
################################################################

#### If the year is a  leap year, add 1 to the number of
#### days in the month of february.

  if leapyear_k93 -y ${YEAR}
  then
      DIM[2]="29"
  fi

#### If single month, set the beginning and ending values for the
#### loop to be the numeric value of that month.

  (( FULLYEAR == FALSE )) && BEG=${MONTH}  END=${MONTH}

#### If full year calendar is to be displayed, set the
#### beginning and ending values for the loop to be 1 and 12.

  if (( FULLYEAR == TRUE  ))
  then
      (( VERBOSE == TRUE )) && print -u 2 -- "# Generating calender for entire year of \"${YEAR}\""
      BEG="1"
      END="12"
  fi

#### Generate a calendar for the the month or year specified,
#### using a loop.

  for (( MON=${BEG}; MON<=${END}; ++MON ))
  do
    unset ROW1 ROW2 ROW3 ROW4 ROW5 ROW6
    typeset -R2 ROW1 ROW2 ROW3 ROW4 ROW5 ROW6

#### Initialize each position of each row of the calendar,
#### since each row represents a week, each row will have 7
#### non-null elements although they may not begin at index
#### position 0.  Initialize each array element for each
#### calendar  row with two blank characters, since each
#### position may contain a double digit number. 

    for (( i=0; i<=6; ++i ))
    do
        ROW1[i]="  "
        ROW2[i+7]="  "
        ROW3[i+14]="  "
        ROW4[i+21]="  "
        ROW5[i+28]="  "
        ROW6[i+35]="  "
    done

#### Determine on which day of the week the first day of the
#### month occurs using the "dow_k93" function.  If "VERBOSE"
#### mode was specified on the command line of this function
#### using a "-v" option, pass it along to  the "dow_k93"
#### function.

    DOWOPT="-y ${YEAR} -m ${MON} -d 1"
    (( VERBOSE == TRUE )) && DOWOPT="${DOWOPT} -v"
    FIRSTDAY="$( dow_k93 ${DOWOPT} )"
    (( VERBOSE == TRUE )) && print -u 2 -- "# ${MNAME[MON]} 1, ${YEAR}...: ${DOWFULL[FIRSTDAY]}"

#### Assign day numbers to each day of the month, beginning
#### on the  day of the week the month starts.  Assign the
#### day numbers sequentially for each row of the calendar. 
#### Some row positions may not have a number  assigned. 
#### Account for the Gregorian Reformation from Sep 2-14,
#### 1752, by skipping Sep 3-13.

    for (( i=${FIRSTDAY}; i<=(${DIM[${MON}]}+${FIRSTDAY}-1); ++i ))
    do

        if (( YEAR == 1752 )) &&
           (( MON  == 9    )) &&
           (( ( i - FIRSTDAY + 1 ) > 2 ))
        then
            (( i >=  0 && i <=  6 )) && ROW1[i]=$(( i - FIRSTDAY + 12 ))
            (( i >=  7 && i <= 13 )) && ROW2[i]=$(( i - FIRSTDAY + 12 ))
            (( i >= 14 && i <= 20 )) && ROW3[i]=$(( i - FIRSTDAY + 12 ))
        else
            (( i >=  0 && i <=  6 )) && ROW1[i]=$(( i - FIRSTDAY + 1 ))
            (( i >=  7 && i <= 13 )) && ROW2[i]=$(( i - FIRSTDAY + 1 ))
            (( i >= 14 && i <= 20 )) && ROW3[i]=$(( i - FIRSTDAY + 1 ))
            (( i >= 21 && i <= 27 )) && ROW4[i]=$(( i - FIRSTDAY + 1 ))
            (( i >= 28 && i <= 34 )) && ROW5[i]=$(( i - FIRSTDAY + 1 ))
            (( i >= 35 && i <= 41 )) && ROW6[i]=$(( i - FIRSTDAY + 1 ))
        fi
    done

#### Determine the length of the string containing the full
#### month name followed by the 4 digit year.  Then center
#### this string over a calendar by subtracting the length
#### from the width of a calendar and divide the result by 2.
#### This is the number of spaces that should be inserted
#### before the "month year" string and after the string as
#### well.

    TLEN=$(( ${#MNAME[${MON}]} + ${#YEAR} + 1 ))

    SPCS=$(( ( WID - TLEN ) / 2 ))
    SUFFIX="${SPCS}"

    IFS=$' \t\n'

#### Store all elements of each row of the calendar in an
#### array to be displayed after all calendars have been
#### generated (if a full year calendar is being generated)

    (( VERBOSE == TRUE )) && print -u 2 -- "# Generating calendar for ${MNAME[MON]}, ${YEAR}"
    CAL1[MON]="${SPACE:0:SPCS}${MNAME[${MON}]} ${YEAR}${SPACE:0:SUFFIX}"
    CAL2[MON]="${DOW2[*]}"
    CAL3[MON]="${ROW1[*]}"
    CAL4[MON]="${ROW2[*]}"
    CAL5[MON]="${ROW3[*]}"
    CAL6[MON]="${ROW4[*]}"
    CAL7[MON]="${ROW5[*]}"
    CAL8[MON]="${ROW6[*]}"

  done

#### If a full year calendar is to be displayed, display the
#### first three months of the year, then the second three
#### months, and so on.  For the three months being displayed
#### at a time, display the first row of each calendar, one
#### after the other all on the same line, then the second
#### line,  and so on.  Continue for each calendar row, then
#### display the next three months, and so on until all
#### months for the year are displayed.

  if (( FULLYEAR == TRUE ))
  then

    print 

    for (( i=1; i<=8; ++i ))
    do
        eval print -- "\"\${CAL${i}[1]}   \${CAL${i}[2]}   \${CAL${i}[3]}\""
    done
    for (( i=1; i<=8; ++i ))
    do
        eval print -- "\"\${CAL${i}[4]}   \${CAL${i}[5]}   \${CAL${i}[6]}\""
    done
    for (( i=1; i<=8; ++i ))
    do
        eval print -- "\"\${CAL${i}[7]}   \${CAL${i}[8]}   \${CAL${i}[9]}\""
    done
    for (( i=1; i<=8; ++i ))
    do
        eval print -- "\"\${CAL${i}[10]}   \${CAL${i}[11]}   \${CAL${i}[12]}\""
    done

    print 

  else

#### If a single month is to be displayed, display  each
#### stored row of the calendar for the month, in sequential
#### order one row after the other.

    for (( i=1; i<=8; ++i ))
    do
        eval print -- "\"\${CAL${i}[${MONTH}]}\""
    done

  fi

  (( VERBOSE  == TRUE )) && print -u 2 -- "# Exiting Function.: ${0}"
  return 0
}
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