How to Use the 'cal' Command (with examples)

The cal command is a simple and effective utility available on Unix-like operating systems that allows users to display calendars in a straightforward manner. This can be useful for anyone looking to quickly view calendar dates without the need for a graphical interface. Besides displaying the current month, it provides various other functionalities such as showcasing specific months, entire years, or even highlighting current dates in a calendar view.

Use case 1: Display a Calendar for the Current Month

Code:

cal

Motivation: For quickly checking the current month’s dates, the basic cal command shows the calendar of the present month. This is particularly useful for anyone who wants to verify dates or plan short-term activities without navigating through digital calendars or applications.

Explanation:

• The cal command, without any additional arguments, defaults to displaying the calendar of the ongoing month. This default behavior is designed to provide immediate, relevant information without needing any date specifics from the user.

Example output:

    October 2023      
Su Mo Tu We Th Fr Sa  
 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 31

Use case 2: Display a Calendar for a Specific Year

Code:

cal 2023

Motivation:
When planning for long-term projects or events spanning multiple months, having a yearly view is beneficial. By displaying a calendar for an entire year, one can gain insight into month sequences, holidays, or special events that may be significant for scheduling or holiday planning.

Explanation:

• cal 2023: The argument 2023 specifies the year for which the calendar should be displayed. The command will output all the months of the specified year.

Example output:

                             2023     
       January               February               March       
Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7               1  2  3  4               1  2  3 
 8  9 10 11 12 13 14    5  6  7  8  9 10 11    4  5  6  7  8  9 10 
15 16 17 18 19 20 21   12 13 14 15 16 17 18   11 12 13 14 15 16 17 
22 23 24 25 26 27 28   19 20 21 22 23 24 25   18 19 20 21 22 23 24 
29 30 31               26 27 28              25 26 27 28 29 30 31 

Use case 3: Display a Calendar for a Specific Month and Year

Code:

cal 10 2023

Motivation: Helps in pinpointing dates or planning activities in a particular month of a specific year. This is particularly advantageous when revisiting historical data or planning future events in a known period.

Explanation:

• cal 10 2023: The argument 10 represents the month (October), and 2023 represents the year, allowing for the display of a specific month within a specified year.

Example output:

    October 2023      
Su Mo Tu We Th Fr Sa  
 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 31

Use case 4: Display the Whole Calendar for the Current Year Using [j]ulian Days

Code:

cal -y -j

Motivation: Julian day numbering provides a sequential count of days within a year, which can be instrumental in fields like astronomy, agriculture, education, and more. This is helpful for datasets or time series analysis which might prefer day-of-year formats over conventional date formats.

Explanation:

• -y: This option instructs the command to print a calendar of the whole current year.
• -j: Enables the Julian day format, meaning each day of the year is numbered incrementally starting from January 1.

Example output:

                             2023     
       January               February               March       
Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7                 31  32    60
 8  9 10 11 12 13 14    30  31  32  33  34  35    59  60  61  62  
15 16 17 18 19 20 21    37  38  39  40  41  42    66  67  68  69
22 23 24 25 26 27 28    35  36  37  38  39  40  54   
29 30 31

Use case 5: [h]ighlight Today and Display [3] Months Spanning the Date

Code:

cal -h -3 10 2023

Motivation: This feature is essential for anyone managing or planning short-term projects across multiple months. Highlighting the current date draws immediate attention, aiding in the tracking of timelines or deadlines.

Explanation:

• -h: Highlights the current day in the calendar view.
• -3: Directs the program to show three months spanning the specified date.
• Parameters 10 and 2023 specify the month (October) and the year, respectively, to define the range of months displayed.

Example output:

   September 2023        October 2023        November 2023
Su Mo Tu We Th Fr Sa  Su Mo Tu We Th Fr Sa  Su Mo Tu We Th Fr Sa
       1  2  3        1  2  3  4  5  6  7          1  2  3  4
 4  5  6  7  8  9 10  8  9 10*11 12 13 14   5  6  7  8  9 10 11
11 12 13 14 15 16 17 15 16 17 18 19 20 21  12 13 14 15 16 17 18
18 19 20 21 22 23 24 22 23 24 25 26 27 28  19 20 21 22 23 24 25
25 26 27 28 29 30    29 30 31             26 27 28 29 30

Use case 6: Display the 2 Months [B]efore and 3 [A]fter a Specific [m]onth of the Current Year

Code:

cal -A 3 -B 2 10

Motivation: Viewing months surrounding a central date can enhance event planning, allowing users to visualize a period across half a year. This can be useful for seasonal businesses or educational academic terms planning.

Explanation:

• -A 3: Displays three months after the specified month.
• -B 2: Displays two months before the specified month.
• 10: Specifies the central month (October) around which the months before and after are displayed.

Example output:

   August 2023        September 2023        October 2023    
Su Mo Tu We Th Fr Sa  Su Mo Tu We Th Fr Sa  Su Mo Tu We Th Fr Sa
    1  2  3  4  5        1  2  3  4  5  6     1  2  3  4  5  6
 6  7  8  9 10 11 12   7  8  9 10 11 12 13   8  9 10 11 12 13 
13 14 15 16 17 18 19  13 14 15 16 17 18 19  15 16 17 18 19 20

Use case 7: Display a Specific Number of Months Before and After ([C]ontext) the Specified Month

Code:

cal -C 5 6

Motivation: Occasionally, it is beneficial to introspect on a larger timeframe around a specific time of interest, which aids in compiling reports or ascertaining patterns over an extended context period.

Explanation:

• -C 5: Allows users to input a number of months post and prior in display, centered on the chosen month.
• 6: Sets June as the central month around which context is built.

Example output:

  February 2023       March 2023        April 2023      
Su Mo Tu We Th Fr Sa  Su Mo Tu We Th Fr Sa  Su Mo Tu We Th Fr Sa
          1  2  3  4           1  2  3  4           1  2  3  4
 5  6  7  8  9 10 11   5  6  7  8  9 10 11   5  6  7  8  9 10
12 13 14 15 16 17 18  12 13 14 15 16 17 18  12 13 14 15 16 17

Use case 8: Specify the Starting [d]ay of the Week

Code:

cal -d 0

Motivation: Each region or country might observe different starting days of the week due to cultural or traditional preferences. Adjusting the calendar view to reflect local practices can provide a more pertinent and practical view for users.

Explanation:

• -d 0: The digit 0 sets Sunday as the first day of the week, as per standard American convention. Changing this number adjusts the week’s start day (e.g., Monday as 1).

Example output:

    September 2023
Su Mo Tu We Th Fr Sa  
    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 

Conclusion:

The versatility of the cal command is apparent through its various use cases, providing quick and accessible insight into calendars across different time scales and formats. Whether for professional scheduling or casual date checking, this command is a valuable tool adaptable for a wide array of users’ needs. By using the various options outlined above, users can not only visualize time frames but also adjust calendars to better align with specific tasks and cultural preferences.