Bash Epoch Timestamp

The date command is the standard tool for Unix timestamps in Bash. Note: Linux (GNU date) and macOS (BSD date) have different syntax for some operations.

Get the current Unix timestamp

Bash

date +%s                            # seconds (works on Linux + macOS)
date +%s%3N                         # milliseconds (GNU/Linux only)
date +%s%N                          # nanoseconds  (GNU/Linux only)

# Store in a variable
NOW=$(date +%s)
echo $NOW

Convert epoch to human-readable date

Bash — Linux (GNU date)

date -d @1700000000
date -d @1700000000 '+%Y-%m-%d %H:%M:%S'   # 2023-11-14 22:13:20
date -d @1700000000 --utc                   # force UTC output
date -d @1700000000 '+%Y-%m-%dT%H:%M:%SZ' --utc  # ISO 8601

Bash — macOS (BSD date)

date -r 1700000000
date -r 1700000000 '+%Y-%m-%d %H:%M:%S'
date -r 1700000000 -u '+%Y-%m-%dT%H:%M:%SZ'  # ISO 8601 UTC

Convert date string to epoch

Bash — Linux (GNU date)

date -d "2023-11-14 22:13:20" +%s
date -d "2023-11-14T22:13:20Z" +%s        # ISO 8601 UTC
date -d "yesterday" +%s
date -d "next monday" +%s
date -d "2 hours ago" +%s

Bash — macOS (BSD date)

date -j -f "%Y-%m-%d %H:%M:%S" "2023-11-14 22:13:20" +%s
date -j -f "%Y-%m-%dT%H:%M:%S" "2023-11-14T22:13:20" +%s

Date arithmetic in scripts

Bash

NOW=$(date +%s)

ONE_HOUR_AGO=$((NOW - 3600))
ONE_DAY_LATER=$((NOW + 86400))
THIRTY_DAYS_AGO=$((NOW - 30 * 86400))

# Check if a file was modified in the last hour
FILE_MOD=$(date -r myfile.log +%s 2>/dev/null || stat -c %Y myfile.log)
if (( NOW - FILE_MOD < 3600 )); then
  echo "File modified within the last hour"
fi

Measure script execution time

Bash

START=$(date +%s)

# ... your script here ...
sleep 2

END=$(date +%s)
ELAPSED=$((END - START))
echo "Elapsed: ${ELAPSED}s"

Cross-platform solution (Python fallback)

Bash

# Works on both Linux and macOS
python3 -c "import time; print(int(time.time()))"

# Convert epoch to date cross-platform
python3 -c "from datetime import datetime,timezone; print(datetime.fromtimestamp(1700000000,tz=timezone.utc))"

→ Use the live epoch converter to convert any shell timestamp instantly.