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Just typing date will print the date and time on the standard output. Following are some useful options with the date command.

• Seconds since UNIX epoch (01/01/1970)

Use %s to get number of seconds passed since UNIX epoch. Creating unique file names is one of the possible use case.

# + is use for formatting
date +%s
# Output: 1589455968

• Number of days since the year's beginning

Use %j to get the number of days passed since the beginning of the year.

# + is use for formatting
date +%j
# Output: 135

• Dates in the past or future

Use -d or --date option to get any date in the past or future.

# + is use for formatting
date +%F -d "1 day ago"
# Output: 2020-05-13

# More easily by using - sign
date +%F -d "-1 day"
# Output: 2020-05-13

date +"%D %T" -d "1 year ago"
# Output: 05/14/19 16:54:02

date +"%F" --date="1 month ago"
# Output: 2020-04-14

# For dates in future use + sign before number
date +%F -d "+1 day"
# Output: 2020-05-15

• Get Time Zone

Use %Z option to get your time zone

# + is use for formatting
date +%Z
# Output: PKT

• Get date from UNIX epoch

To extract date from the number of seconds passed since UNIX epoch, use -d with @.

date -d @1500000000
# Output: Fri 14 Jul 07:40:00 PKT 2017

• Get date in ISO Format

Use -Iseconds option to get current date in ISO Format.

date -Iseconds
# Output: 2020-05-14T17:18:22+05:00

• Get the last day of the previous month

While executing an SQL command to retrieve data for the starting and ending date of the previous month, it is always a point of concern to correctly determine whether the previous month was of 30 or 31 days. To resolve this issue, we can use date in the option argument of date command with %d option to get the current day of the month.

# + is use for formatting
# %d is used to get the day of the month

date +%F -d "$(date +%d) days ago"
# Output: 2020-04-30

I hope it will help you. Keep coding!

P.S. I will keep on adding to this post with time.