Cookbooks
Bash
Chapter 7. Dates and Times
Calculating a date in the future or past

Bash:
Calculating a date in the future or past

How to:

In Bash, you can use the date command along with the -d flag to manipulate dates. Here’s how:

# Current Date
date

# Future Date: 10 days from now
date -d "+10 days"

# Past Date: 10 days ago
date -d "-10 days"

# Specific Future Date: Adding weeks, months, years
date -d "+1 month"
date -d "+2 weeks"
date -d "+1 year"

# Sample output for future date
Mon 31 Jan 2023 12:34:56 PM PST

Deep Dive

Manipulating dates is a common requirement in scripting and programming. Historically, this task was more cumbersome and error-prone when handling leap years, timezones, etc. In Unix-like systems, the date command has evolved to include options for easy date calculation.

Alternatives include using shell arithmetic or external tools like awk or perl for more complex date logic, but the date command remains the easiest and most straightforward for basic operations. Under the hood, the date command uses system libraries to handle the complexity of time calculation, abstracting this from the user.

See Also

Comparing two dates