How to use date command in day to day practical usage

In this article, we will learn about the date command in Linux and how to practically use it in day-to-day usage with some practical examples. The date command is used to print or change the system date and time, making it an essential tool for system administrators and users.

General Syntax

[root@localhost ~]# date [OPTION]... [+FORMAT]
[root@localhost ~]# date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]

Key Features of the Date Command

• Print current date and time on the system

• Display date and time in custom formats

• Read dates from files

• Display Universal Coordinated Time (UTC)

• Set system date and time

• Calculate past and future dates

Basic Usage Examples

Displaying Current Date and Time

[root@localhost ~]# date
Wed Jun 15 04:10:29 IST 2016

Parsing Date from String

The --date option allows you to parse and display dates from various string formats −

[root@localhost ~]# date --date="6/15/2016"
Wed Jun 15 00:00:00 IST 2016

[root@localhost ~]# date --date="next Monday"
Mon Jun 20 04:10:29 IST 2016

Reading Dates from Files

Use the --file option to read dates from a file. Create a sample file first −

[root@localhost ~]# vi samplelog.txt
# File contents:
04 jun 1978
03 aug 1980
24 feb 2004
22 dec 2007

[root@localhost ~]# date --file=samplelog.txt

Sun Jun  4 00:00:00 IST 1978
Thu Aug  3 00:00:00 IST 1980
Tue Feb 24 00:00:00 IST 2004
Sat Dec 22 00:00:00 IST 2007

Working with Past and Future Dates

The date command excels at calculating relative dates using natural language expressions −

[root@localhost ~]# date --date='1 day ago'
Tue Jun 14 16:01:31 IST 2016

[root@localhost ~]# date --date='yesterday'
Tue Jun 14 16:03:01 IST 2016

[root@localhost ~]# date --date='1 month ago'
Sun May 15 16:03:35 IST 2016

[root@localhost ~]# date --date='1 year ago'
Mon Jun 15 16:03:57 IST 2015

[root@localhost ~]# date --date='next Friday'
Fri Jun 17 16:04:12 IST 2016

Setting System Date and Time

Use the -s option to set the system date and time (requires root privileges) −

# date -s "Tue June 15 04:08:37 IST 2016"
Wed Jun 15 04:08:37 IST 2016

Working with Time Zones

Displaying UTC Time

[root@localhost ~]# date
Wed Jun 15 04:10:29 IST 2016

[root@localhost ~]# date -u
Tue Jun 14 22:40:31 UTC 2016

Converting Time Zones

[root@localhost ~]# date -d '2016-05-20 18:00 CST'
Sat May 21 05:30:00 IST 2016

File Timestamps

Check when a file was last modified using the -r option −

[root@localhost ~]# date -r samplelog.txt
Wed Jun 15 15:45:37 IST 2016

Custom Date Formatting

The date command supports extensive formatting options. Here are the most commonly used format specifiers −

Practical Format Examples

[root@localhost ~]# date +"%Y-%m-%d"
2016-06-15

[root@localhost ~]# date +"%B %d, %Y"
June 15, 2016

[root@localhost ~]# date +"%A, %b %d at %I:%M %p"
Wednesday, Jun 15 at 04:10 PM

[root@localhost ~]# date +"%s"
1466011829

Common Use Cases

• Log file naming: logfile_$(date +%Y%m%d).log

• Backup scripts: backup_$(date +%Y%m%d_%H%M%S).tar.gz

• Scheduling validation: Check if current time meets specific criteria

• Time zone conversions: Convert timestamps between different zones

• Date arithmetic: Calculate deadlines, intervals, and relative dates

Conclusion

The date command is a powerful and versatile tool for handling date and time operations in Linux. From basic display functions to complex date arithmetic and formatting, it serves as an essential utility for system administration, scripting, and daily command-line tasks. Its ability to parse natural language date expressions and work with multiple time zones makes it indispensable for modern system management.