Friday Fun – Does Anyone Really Know What Day It Is?

This week's Friday Fun I think epitomizes how much I think about PowerShell. But I also think it will serve as a useful learning device if not something you might actually want to use. For some reason, I thought it would be useful to quickly display a monthly calendar in PowerShell. Sure, I could click over to the clock on the start bar and navigate to a calendar. But then I have to take my hands off the keyboard and click around with a mouse. I'd much rather type a quick command, maybe give it a date and see the results. So this is what I came up with: Get-Calendar.

#requires -version 2.0

Function Get-Calendar {

<#
.Synopsis
Display a monthly calendar
.Description
This command will display calendar month based on the given date.
.Example
PS C:\> get-calendar

      September 2014
Sun Mon Tue Wed Thu Fri Sat
      1   2   3   4   5   6
  7   8   9  10  11  12  13
 14  15  16  17  18  19  20
 21  22  23  24  25  26  27
 28  29  30
 .Example
 PS C:> 1..12 | foreach {get-calendar "$_/1/2015"} | Out-file c:\work\2015.txt
Create a calendar text file for 2015 using a North American date format.
.Notes
Last Updated: September 16, 2014
Version     : 1.0

Learn more:
 PowerShell in Depth: An Administrator's Guide (http://www.manning.com/jones6/)
 PowerShell Deep Dives (http://manning.com/hicks/)
 Learn PowerShell 3 in a Month of Lunches (http://manning.com/jones3/)
 Learn PowerShell Toolmaking in a Month of Lunches (http://manning.com/jones4/)

.Link
https://jdhitsolutions.com/blog/2014/09/friday-fun-does-anyone-really-know-what-day-it-is
.Link
Get-Date
Get-Culture
#>

[cmdletbinding()]
Param(
[Parameter(Position=0)]
[ValidateNotNullorEmpty()]
[datetime]$Date = (Get-Date)
)

#get some information about weekday names that is culture specific
$cult = Get-Culture
$cal = $cult.Calendar
$ui = Get-UICulture

$daysOfWeek = $ui.DateTimeFormat.AbbreviatedDayNames
$startWeek = $daysOfWeek[0]
#create a string with the days of the week
$days = $DaysOfWeek -join " "

#how many days in the month
$intDays = $cal.GetDaysInMonth($Date.year,$Date.month)

#get the first day of the month
[datetime]$firstday = $Date.addDays(-$Date.Day+1)

<#
I want to align each row of weekdays with the days of the week header.
I need to align the first day of the first week.
#>

$week1=@()
for ($i=0;$i -lt 7;$i++) {
if (("{0:ddd}" -f $firstday) -eq $ui.DateTimeFormat.AbbreviatedDayNames[$i] ) {
  #I am assuming all short day abbreviations will be 3 characters
  $week1+=$firstday.Day.ToString().PadLeft(3)
  #got the date so move on
  break
}
else {
 #add an empty day
 $week1+="   "
} 
}

#fill out the rest of the week
$j = 1
#loop through until we reach the end of the week
while ($i -le 5) {
    $week1+=$firstday.AddDays($j).day.ToString().PadLeft(3)
    $i++
    $j++
}

#construct a centered header
$MonthYear = "{0:MMMM yyyy}" -f $Date
$pad = ($days.Length/2) + ($Monthyear.length/2)
$title = $monthYear.PadLeft($pad)

#define a here string for the final calendar output
$myCal=@"

$title
$days
$($week1 -join " ")`n
"@

#process the rest of the weeks
for ($k=2;$k -le 5;$k++ ) {
 #initialize an array for a week of days
 $wkArray = @()
 for ($i = 0; $i -le 6; $i++) { 
  #get the next day
  $nextday = $firstday.AddDays($j)

  #test if we are still in the same month
  if ($nextday.Month -eq $firstday.month) {
    #add the padded day to the array
    $wkArray+= $nextday.day.ToString().PadLeft(3)
    $j++
  } 
  else {
    #new month so break out of the inner For loop
    Break
  }
 }
 #join each element of the array into a single line
 #and add to the calendar string
 $myCal+= "$($wkArray -join " ")`n"
}

#write out as separate lines which makes it easier to save to a file
$mycal.Split("`n")

} #end function

Set-Alias -Name gcal -Value Get-Calendar

The script will define an alias, gcal, for the function.

Because calendars are culture (i.e. language) specific, I wanted to write something that anyone could use, and not something just for North American users. That meant retrieving culture settings so I could use language specific versions of days of the week. I think. It is very hard to fully test this without a system running completely in a different culture.

I wanted my calendar to display abbreviated week day names in the correct culture.

$cult = Get-Culture
$cal = $cult.Calendar
$ui = Get-UICulture

$daysOfWeek = $ui.DateTimeFormat.AbbreviatedDayNames

After quite a bit of experimenting, I realized the best way to create the calendar was to write each line as a separate string. This meant one line would be the abbreviated week day names.

#create a string with the days of the week
$days = $DaysOfWeek -join " "

Then each week would be a string of numbers. But this was the tricky part. It was easy enough to find out how many days were in the month, and what the first day of the month would be.

$intDays = $cal.GetDaysInMonth($Date.year,$Date.month)

#get the first day of the month
[datetime]$firstday = $Date.addDays(-$Date.Day+1)

Here's the challenge: I can figure out that the first day of the month might be on a Thursday. Which means I need to align '1' under the THU heading, and then add enough other days until I reach the end of the week.

$week1=@()
for ($i=0;$i -lt 7;$i++) {
if (("{0:ddd}" -f $firstday) -eq $ui.DateTimeFormat.AbbreviatedDayNames[$i] ) {
  #I am assuming all short day abbreviations will be 3 characters
  $week1+=$firstday.Day.ToString().PadLeft(3)
  #got the date so move on
  break
}
else {
 #add an empty day
 $week1+="   "
} 
}

So I created an array, $Week1, to hold a set of values. I use a FOR loop to check if the date's short day name matches the array of abbreviated day names from the UI culture, I know that is the first day of the month. Otherwise, I simply add a 2 space "filler" to the array. Then I need to add the rest of the days for the first week.

#fill out the rest of the week
$j = 1
#loop through until we reach the end of the week
while ($i -le 5) {
    $week1+=$firstday.AddDays($j).day.ToString().PadLeft(3)
    $i++
    $j++
}

With that, I can begin constructing a text representation of the calendar using a here string.

#define a here string for the final calendar output
$myCal=@"

$title
$days
$($week1 -join " ")`n
"@

The clever part is using the -Join operator to essentially concatenate all of the values in the week 1 array, separating each by a space. From here, I repeat the process for each week until I reach the end of the month.

At the end of the process $mycal is a here string with the calendar. I could simply write $mycal to the pipeline and it would look just fine. However, because you might want to save the calendar to a text file, I found it best to split the here string back into an array.

#write out as separate lines which makes it easier to save to a file
$mycal.Split("`n")

Now you can create a text file calendar for next year:

1..12 | foreach {get-calendar "$_/1/2015"} | Out-file c:\work\2015.txt

Or run the command at the prompt.

The function defaults to the current month or you can specify any date. You can even write it to the host and add a little color.

If you run PowerShell under something other than en-US, I'd love to hear how this works for you. Hope you have a little bit of fun with this.

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