Bash Script to Convert Unix Timestamp to Date

Use the Bash command date -d @ to convert a Unix timestamp to a readable date, for example, date -d @1633072800 outputs the date for that timestamp.

Examples

Input0

OutputThu Jan 1 00:00:00 UTC 1970

Input1633072800

OutputFri Oct 1 00:00:00 UTC 2021

Input9999999999

OutputSat Nov 20 17:46:39 UTC 2286

How to Think About It

To convert a Unix timestamp to a date, think of the timestamp as the number of seconds since January 1, 1970. The Bash date command can interpret this number and display it as a normal date by using the -d option with an @ symbol before the timestamp.

Algorithm

1

Get the Unix timestamp input from the user or script argument.

2

Use the <code>date</code> command with the <code>-d</code> option and prefix the timestamp with @.

3

Print the output which is the human-readable date.

Code

bash

#!/bin/bash

# Read timestamp from argument
timestamp=$1

# Convert and print date
converted_date=$(date -d @$timestamp)
echo "$converted_date"

Output

Fri Oct  1 00:00:00 UTC 2021

Dry Run

Let's trace the timestamp 1633072800 through the code

1

Get input

timestamp=1633072800

2

Convert timestamp to date

date -d @1633072800 returns 'Fri Oct 1 00:00:00 UTC 2021'

3

Print result

Output: Fri Oct 1 00:00:00 UTC 2021

Step	Action	Value
1	Input timestamp	1633072800
2	date command output	Fri Oct 1 00:00:00 UTC 2021
3	Printed output	Fri Oct 1 00:00:00 UTC 2021

Why This Works

Step 1: Understanding Unix timestamp

A Unix timestamp counts seconds from 1970-01-01 00:00:00 UTC, so converting it means finding the date that many seconds later.

Step 2: Using date command

The Bash date command with -d @timestamp tells the system to interpret the number as seconds since epoch and format it as a date.

Step 3: Output formatting

The output is a human-readable date string showing day, month, time, and timezone for easy understanding.

Alternative Approaches

Using printf and date

bash

#!/bin/bash

timestamp=$1
printf '%(%Y-%m-%d %H:%M:%S)T\n' "$timestamp"

This uses Bash's built-in printf with format specifiers for a cleaner date format but requires Bash 4.2+.

Using Python one-liner

bash

python3 -c "import datetime, sys; print(datetime.datetime.utcfromtimestamp(int(sys.argv[1])))" 1633072800

Runs a Python command to convert timestamp, useful if date command is limited or unavailable.

Complexity: O(1) time, O(1) space

Time Complexity

The conversion uses a direct system call without loops, so it runs in constant time.

Space Complexity

Only a few variables are used to hold input and output, so space usage is constant.

Which Approach is Fastest?

Using the Bash date command is fastest and simplest; Python adds overhead but offers flexibility.

Approach	Time	Space	Best For
Bash date -d @timestamp	O(1)	O(1)	Simple and fast conversion
Bash printf with format	O(1)	O(1)	Formatted output with Bash 4.2+
Python one-liner	O(1)	O(1)	When date command is limited or for complex formatting