date / cal

Display the current date and time.

date

Display with a format string.

date +format_string

Assign a formatted date to a variable.

today=$(date +%Y-%m-%d)

Display a specific date and time (GNU date only).

date -d "datetime_string"

Calculate a date N days in the past or future (GNU date only).

date -d "7 days ago" +%Y-%m-%d

Display this month's calendar.

cal

     March 2026
Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31

Specifying a year displays a full year calendar.

cal 2026

Specifying a month and year displays that month's calendar.

cal 3 2026

     March 2026
Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31

Format	Description / Output Example
%Y	Four-digit year (e.g., 2026).
%m	Month (01–12).
%d	Day of the month (01–31).
%H	Hour in 24-hour format (00–23).
%M	Minute (00–59).
%S	Second (00–59).
%A	Full weekday name in English (e.g., Friday).
%a	Abbreviated weekday name in English (e.g., Fri).
%B	Full month name in English (e.g., March).
%s	Unix timestamp (seconds since the epoch).
%Z	Timezone name (e.g., JST).
%Y%m%d	YYYYMMDD format (e.g., 20260306).
%Y-%m-%d %H:%M:%S	ISO 8601-style format (e.g., 2026-03-06 12:00:00).

Display the current date and time.

date
Fri Mar  6 12:00:00 JST 2026

Display the date and datetime using format strings.

echo "Today: $(date +%Y-%m-%d)"
Today: 2026-03-06

echo "Now: $(date '+%Y-%m-%d %H:%M:%S')"
Now: 2026-03-06 12:00:00

Written as a shell script, it looks like this.

date_sample.sh

echo "Today: $(date +%Y-%m-%d)"
echo "Now: $(date '+%Y-%m-%d %H:%M:%S')"

bash date_sample.sh
Today: 2026-03-06
Now: 2026-03-06 12:00:00

Use a date in a backup file name.

backup.sh

today=$(date +%Y%m%d)
tar -czf "backup_${today}.tar.gz" /var/www/html/
echo "Backup complete: backup_${today}.tar.gz"

bash backup.sh
Backup complete: backup_20260306.tar.gz

Define a function that prepends a timestamp to log messages. The following is written as a shell script.

log_sample.sh

log() {
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*"
}
log "Process started"
log "Data retrieval complete"

bash log_sample.sh
[2026-03-06 12:00:00] Process started
[2026-03-06 12:00:03] Data retrieval complete

You can also enter a function definition directly in the terminal. After pressing Enter following the {, a > prompt appears — this means input is still expected. Enter } to complete the definition.

log() {
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*"
}
log "Process started"
[2026-03-06 12:00:00] Process started
log "Data retrieval complete"
[2026-03-06 12:00:03] Data retrieval complete

Measure elapsed time using Unix timestamps. The following is written as a shell script.

timer.sh

start=$(date +%s)
sleep 2
end=$(date +%s)
echo "Elapsed time: $((end - start)) seconds"

bash timer.sh
Elapsed time: 2 seconds

Calculate relative dates with GNU date (Linux). The following is written as a shell script.

date_calc.sh

# Date 7 days from now (Linux)
date -d "7 days" +%Y-%m-%d

# Date 7 days ago (Linux)
date -d "7 days ago" +%Y-%m-%d

bash date_calc.sh
2026-03-13
2026-02-27

On macOS (BSD date), use the -v option instead.

date_calc.sh

# Date 7 days from now (macOS)
date -v+7d +%Y-%m-%d

# Date 7 days ago (macOS)
date -v-7d +%Y-%m-%d

bash date_calc.sh
2026-03-13
2026-02-27

Display a calendar.

cal 3 2026
     March 2026
Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31

For naming backups in scripts, $(date +%Y%m%d) and $(date +%Y%m%d_%H%M%S) are the standard conventions. For log output, wrapping $(date '+%Y-%m-%d %H:%M:%S') in a function keeps your code clean and reusable.

Relative date calculation with date -d is a GNU date (Linux) feature. On macOS (BSD date), write it as date -v+7d instead. For portable scripts, you can also use python3 -c "from datetime import..." as an alternative.