date Command Examples - Linux Reference

About date

date displays or sets the system date and time. It's essential for logging, timestamps, scheduling, and date calculations.

Basic Syntax: date [OPTION]... [+FORMAT]

Key Format Specifiers: %Y (year), %m (month), %d (day), %H (hour), %M (minute), %S (second), %A (weekday), %B (month name)

Example 1: Basic Date Display

Display current date and time in various default formats.

# Default format
date

# ISO 8601 format
date -I
date --iso-8601

# RFC 5322 format (email headers)
date -R

# UTC time
date -u
date --utc

Output:

Tue Nov 12 15:36:31 EST 2025
2025-11-12
Tue, 12 Nov 2025 15:36:31 -0500
Tue Nov 12 20:36:31 UTC 2025

Example 2: Custom Date Formatting

Create custom date formats using format specifiers.

# Standard formats
date '+%Y-%m-%d'
date '+%H:%M:%S'
date '+%Y-%m-%d %H:%M:%S'

# Verbose formats
date '+%A, %B %d, %Y'
date '+%I:%M %p on %A'

# Compact formats
date '+%Y%m%d'
date '+%Y%m%d_%H%M%S'

# Custom delimiters
date '+%d/%m/%Y'
date '+%m-%d-%Y'

Output:

2025-11-12
15:36:31
2025-11-12 15:36:31
Tuesday, November 12, 2025
03:36 PM on Tuesday
20251112
20251112_153631

Note:

The + sign is required before format strings. Combine multiple specifiers to create any date format needed.

Example 3: Timestamps for Files and Logs

Generate timestamps perfect for filenames and logging.

# Create timestamped backup
tar -czf backup_$(date +%Y%m%d).tar.gz /data/

# Log with timestamp
echo "$(date '+%Y-%m-%d %H:%M:%S') - Backup completed" >> backup.log

# Timestamped filename
touch report_$(date +%Y-%m-%d_%H-%M-%S).txt

# ISO 8601 with seconds
date '+%Y-%m-%dT%H:%M:%S'

# Unix epoch timestamp
date +%s

# Epoch with milliseconds
date +%s%3N

Examples:

backup_20251112.tar.gz
2025-11-12 15:36:31 - Backup completed
report_2025-11-12_15-36-31.txt
2025-11-12T15:36:31
1731441391
1731441391123

Example 4: Date Arithmetic

Calculate dates in the past or future.

# Tomorrow
date -d "tomorrow"
date -d "+1 day"

# Yesterday
date -d "yesterday"
date -d "-1 day"

# Next week
date -d "+1 week"
date -d "+7 days"

# 30 days ago
date -d "-30 days" '+%Y-%m-%d'

# Specific date operations
date -d "2025-01-01 +90 days"

# Next month
date -d "+1 month"

# Complex calculations
date -d "2025-11-12 +2 weeks +3 days"

Output:

Wed Nov 13 15:36:31 EST 2025
Mon Nov 11 15:36:31 EST 2025
Tue Nov 19 15:36:31 EST 2025
2025-10-13
Wed Apr 01 00:00:00 EDT 2025

Note:

Use -d or --date for relative dates. Supports days, weeks, months, years, hours, minutes, seconds.

Example 5: Parsing and Converting Dates

Convert between different date formats and parse date strings.

# Parse specific date
date -d "2025-11-12"
date -d "Nov 12, 2025"
date -d "11/12/2025"

# Parse with time
date -d "2025-11-12 15:30:00"

# Convert to different format
date -d "2025-11-12" '+%A, %B %d, %Y'

# Parse epoch timestamp
date -d @1731441391

# Convert epoch to readable
date -d @1731441391 '+%Y-%m-%d %H:%M:%S'

# ISO to RFC format
date -d "2025-11-12T15:30:00" -R

Output:

Tue Nov 12 00:00:00 EST 2025
Tuesday, November 12, 2025
Tue Nov 12 15:36:31 EST 2025
2025-11-12 15:36:31

Example 6: Working with Different Time Zones

Display times in different time zones using TZ environment variable.

# UTC time
TZ=UTC date

# Different time zones
TZ=America/New_York date
TZ=America/Los_Angeles date
TZ=Europe/London date
TZ=Asia/Tokyo date

# Show multiple zones
for tz in UTC America/New_York Europe/London Asia/Tokyo; do
    echo "$tz: $(TZ=$tz date '+%H:%M')"
done

# Convert specific time to different zone
TZ=Asia/Tokyo date -d "TZ=\"America/New_York\" 2025-11-12 15:00"

Output:

Tue Nov 12 20:36:31 UTC 2025
Tue Nov 12 15:36:31 EST 2025
Tue Nov 12 12:36:31 PST 2025
Tue Nov 12 20:36:31 GMT 2025
Wed Nov 13 05:36:31 JST 2025

Example 7: Day of Week and Date Components

Extract specific date components and calculate day of week.

# Day of week
date '+%A'
date '+%a'
date '+%u'  # 1-7 (Monday=1)
date '+%w'  # 0-6 (Sunday=0)

# Month names
date '+%B'  # Full month name
date '+%b'  # Abbreviated

# Various components
date '+%Y'  # Year
date '+%m'  # Month (01-12)
date '+%d'  # Day (01-31)
date '+%j'  # Day of year (001-366)
date '+%V'  # Week number (ISO)

# Find day of specific date
date -d "2025-12-25" '+%A'

# Check if date is weekend
day=$(date '+%u')
[ $day -gt 5 ] && echo "Weekend" || echo "Weekday"

Output:

Tuesday
Tue
2
2
November
Nov
Thursday

Example 8: Calculating Time Differences

Calculate elapsed time and differences between dates.

# Calculate days between dates
start=$(date -d "2025-01-01" +%s)
end=$(date -d "2025-11-12" +%s)
diff=$((($end - $start) / 86400))
echo "$diff days"

# Time since epoch
date +%s

# Days until specific date
target=$(date -d "2025-12-31" +%s)
now=$(date +%s)
days_until=$(( ($target - $now) / 86400 ))
echo "$days_until days until end of year"

# Time script execution
start_time=$(date +%s)
# ... commands here ...
end_time=$(date +%s)
echo "Elapsed: $(($end_time - $start_time)) seconds"

# Age calculation
birthdate=$(date -d "1990-01-01" +%s)
now=$(date +%s)
age=$(( ($now - $birthdate) / 31536000 ))
echo "$age years old"

Output:

316 days
49 days until end of year
Elapsed: 45 seconds
35 years old

Example 9: Scheduling and Cron-Related Uses

Use date for scheduling, cron jobs, and periodic tasks.

# First day of month check
if [ $(date +%d) -eq 1 ]; then
    echo "First day of month - run monthly tasks"
fi

# First Monday of month
if [ $(date +%d) -le 7 ] && [ $(date +%u) -eq 1 ]; then
    echo "First Monday"
fi

# Business hours check
hour=$(date +%H)
if [ $hour -ge 9 ] && [ $hour -lt 17 ]; then
    echo "Business hours"
fi

# Weekend check
[ $(date +%u) -gt 5 ] && echo "Weekend mode" || echo "Weekday mode"

# Quarter check
month=$(date +%m)
case $month in
    01|02|03) quarter=Q1 ;;
    04|05|06) quarter=Q2 ;;
    07|08|09) quarter=Q3 ;;
    10|11|12) quarter=Q4 ;;
esac
echo "Current quarter: $quarter"

Example 10: Practical Scripting Examples

Real-world date usage in scripts and automation.

# Rotating log files
log_file="app_$(date +%Y%m%d).log"
echo "$(date '+%Y-%m-%d %H:%M:%S') - Application started" >> "$log_file"

# Archive old files
find /logs -name "*.log" -mtime +30 -exec \
    mv {} archive/archive_$(date +%Y%m%d)_{} \;

# Daily backup script
backup_dir="/backup/$(date +%Y/%m/%d)"
mkdir -p "$backup_dir"
tar -czf "$backup_dir/backup_$(date +%H%M%S).tar.gz" /data/

# Report generation
cat << EOF > report.txt
System Report
Generated: $(date '+%A, %B %d, %Y at %I:%M %p')
Uptime: $(uptime -p)
EOF

# Expiration check
expiry_date="2025-12-31"
expiry_epoch=$(date -d "$expiry_date" +%s)
now_epoch=$(date +%s)
if [ $now_epoch -gt $expiry_epoch ]; then
    echo "License expired"
else
    days_left=$(( ($expiry_epoch - $now_epoch) / 86400 ))
    echo "License valid for $days_left days"
fi

Additional Tips & Best Practices

ISO 8601: Use date -I for sortable dates. Add time with date -Iseconds
Epoch time: Unix timestamp (date +%s) is perfect for calculations and databases
Portability: GNU date (-d option) differs from BSD/macOS date. Check with date --version
File modification time: Use date -r filename to show file's modification time
Set system time: Requires root: sudo date -s "2025-11-12 15:30:00" (use NTP instead)
Hardware clock: Use hwclock to sync hardware clock with system time
NTP sync: Prefer ntpdate or timedatectl over manual date setting
Locale: Date format affected by LC_TIME. Set with LANG=en_US.UTF-8 date
Filename safety: Avoid spaces in date formats for filenames. Use underscores or hyphens
Leap years: date handles leap years, daylight saving, and timezone changes automatically
Performance: Cache epoch time in loops: now=$(date +%s) then reuse $now
Debugging: Use date -d to test date parsing before using in scripts