Convert Epoch Timestamp to Readable Date in Linux

In the Linux operating system, Unix epoch timestamps—which count the number of seconds elapsed since January 1, 1970 (UTC)—can be converted into human-readable date and time formats using the native date command. By passing the @ symbol followed by the timestamp to the -d or --date flag, Linux parses the numeric value and translates it into a standard calendar date, allowing users to customize timezones and output formats directly from the command line.

The Basic Conversion Syntax

The GNU date utility found in most Linux distributions uses the -d (or --date) option to accept input strings. To specify an epoch timestamp, prefix the numeric value with the @ symbol:

date -d @1704067200

Output:

Mon Jan  1 00:00:00 UTC 2024

(Note: The actual output time zone will default to your system's configured local timezone.)

Converting to UTC

By default, the date command displays the converted epoch time according to the local timezone configured on your system. To view the timestamp in Coordinated Universal Time (UTC), add the -u (or --utc) flag:

date -u -d @1704067200

Customizing the Output Format

The date command allows formatting the output using format specifiers prefixed by a + sign. This allows you to extract specific date components or adhere to standard formats like ISO 8601.

Standard Date and Time (YYYY-MM-DD HH:MM:SS):
```
date -d @1704067200 +"%Y-%m-%d %H:%M:%S"
```
Output: 2024-01-01 00:00:00
Date Only:
```
date -d @1704067200 +"%F"
```
Output: 2024-01-01
Time with Timezone:
```
date -d @1704067200 +"%T %Z"
```
Output: 00:00:00 UTC

Handling Milliseconds

The standard date command expects epoch values in seconds. If you have a 13-digit millisecond timestamp (common in web applications), you must convert it to seconds before passing it to date. This can be done in Bash using arithmetic expansion:

epoch_ms=1704067200000
date -d @$((epoch_ms / 1000))

BSD/macOS Differences

While GNU date is standard across Linux, macOS and BSD variants use a different syntax for epoch conversion. On BSD systems, the -r flag is used instead:

date -r 1704067200