Epoch Converter on Linux — Bash Commands for Unix Timestamps

Linux has built-in epoch conversion. The date command handles everything. Here are the commands you need, plus the macOS differences that trip everyone up.

Essential Commands

Get Current Timestamp

date +%s → 1712345678

Milliseconds: date +%s%3N → 1712345678123

Epoch to Date

date -d @1712345678 → Fri Apr 5 18:14:38 UTC 2024

Custom format: date -d @1712345678 +"%Y-%m-%d %H:%M:%S" → 2024-04-05 18:14:38

Date to Epoch

date -d "2026-04-06 14:30:00" +%s → 1775574600

date -d "next Friday" +%s → timestamp for next Friday

date -d "2 hours ago" +%s → timestamp from 2 hours ago

Quick Reference

Task	Linux (GNU)	macOS (BSD)
Current epoch	date +%s	date +%s
Epoch to date	date -d @1712345678	date -r 1712345678
Date to epoch	date -d "2026-04-06" +%s	date -j -f "%Y-%m-%d" "2026-04-06" +%s
UTC output	date -u -d @1712345678	date -u -r 1712345678
Custom format	date -d @N +"%Y-%m-%d"	date -r N +"%Y-%m-%d"

The macOS Gotcha

macOS ships with BSD date, not GNU date. The -d @ syntax does not work. Use -r instead:

• Linux: date -d @1712345678
• macOS: date -r 1712345678

Install GNU coreutils via Homebrew (brew install coreutils) to get gdate which uses Linux syntax.

Scripting Patterns

Check if a timestamp has expired:

NOW=$(date +%s)
EXPIRY=1775944800
if [ "$NOW" -gt "$EXPIRY" ]; then
  echo "Expired"
else
  echo "Still valid"
fi

Calculate elapsed time:

START=$(date +%s)
# ... do work ...
END=$(date +%s)
echo "Took $((END - START)) seconds"

When the Terminal Is Overkill

If you are reading docs, debugging an API response, or checking a JWT claim and just need to convert one timestamp quickly, the browser-based converter is faster than remembering whether it is -d @ or -r.

Related: Cron Generator, Regex Tester, JSON Formatter.