# Dates and Times

date followed by + and a pattern prints a date in the shape you need, such as date +%F for 2026-11-09; date -d works out other days, such as 7 days ago; date +%s counts seconds, for timing a job; and a Mac's date uses -v instead of -d.

Journeyman · Unix · Linux · Updated November 10, 2026

## After this lesson you can

- Print a date in the format you need with date +%F and other % codes, and put it in a file name
- Work out other dates with date -d, such as 7 days ago, and time a job with date +%s

## Key takeaways

- date +%F prints the date as year-month-day, which also sorts in date order. %Y, %m, %d, %A and %B give its parts.
- "notes-$(date +%F).txt" puts the date in a file name, so every day gets its own file.
- date -d '7 days ago' +%F works out another day. -d understands yesterday, next friday and a date such as 2026-12-24.
- A Mac's date has no -d: date -v-7d +%F is a week ago there. Or install coreutils with Homebrew and use gdate.
- date +%s is the number of seconds since 1970. Take one reading from another to time a job.

A weather report should say which day it's for. A notes file you save every evening needs a name that says which evening. A cleanup script should delete only the backups more than a week old. Each of those starts with "what's the date?", and a script has to ask the computer, because nobody is there to type it. Administrators put the date on every backup and log they make, and data analysts on every export. *Values from Commands: $( ) and $(( ))* met `date +%F`; this lesson goes further: other shapes, other days, and counting seconds.

## Today, in the shape you need

`date`, then `+` and a pattern, prints the parts of the date you ask for. Each `%` and a letter (read "percent F" and so on) stands for one part, and everything else is printed as written. A pattern with spaces goes in quotes:

```bash
date +%F
date '+%A, %B %d, %Y'
date +%d/%m/%Y
```

```text
2026-11-09
Monday, November 09, 2026
09/11/2026
```

Yours will show the day you run it. These codes cover most jobs:

| Code | Means | Example |
|---|---|---|
| `%F` | the full date, the same as `%Y-%m-%d` | 2026-11-09 |
| `%Y` | the year | 2026 |
| `%m` | the month's number | 11 |
| `%d` | the day of the month | 09 |
| `%A` | the day's name | Monday |
| `%B` | the month's name | November |
| `%H`, `%M`, `%S` | the hour (00 to 23), the minute and the second | 07, 45, 00 |

`%F` is the one to choose for anything a computer sorts. Year first, then month, then day means that sorting the dates as text puts them in date order, which is why it's the international standard way to write a date (ISO 8601).

## A date in a file name

`$( )` puts the output of `date` into another command. These lines save tonight's notes under today's date:

```bash
mkdir -p ~/terminal-practice/dates && cd ~/terminal-practice/dates
echo "Fixed the bike's back tire" > notes.txt
cp notes.txt "notes-$(date +%F).txt"
ls
```

```text
notes-2026-11-09.txt  notes.txt
```

Run the `cp` line again tomorrow and you get a second dated file, instead of replacing this one. For a job that runs more than once a day, add the hour and minute, `date +%F_%H%M`, for names such as `notes-2026-11-09_0745.txt`.

## Other days: date -d

`-d` (read "date of") tells `date` which day to describe, in plain words or as a date:

```bash
date -d yesterday +%F
date -d '7 days ago' +%F
date -d 'next friday' +%F
date -d 2026-12-24 +%A
```

```text
2026-11-08
2026-11-02
2026-11-13
Thursday
```

It also understands `tomorrow`, `3 months ago`, `2 weeks` (from today) and `'2026-12-24 + 7 days'`. A phrase it can't read stops with an *invalid date* error. Ubuntu 26.04's `date` is a newer rewrite of the classic tool: it understands the same phrases, though a message can be worded a little differently on other Linux systems.

**On a Mac, `date` has no `-d`.** Its `-v` moves the date instead: `date -v-7d +%F` is a week ago, and `date -v+1d +%A` is tomorrow's name. Or install Homebrew's coreutils (`brew install coreutils`) and use `gdate`, which works exactly as this lesson shows. The `+` patterns are the same on both.

Dates written as `%F` compare correctly as text, so a cleanup script can ask whether a dated file is more than a week old. Inside `[[ ]]`, `<` (read "comes before") compares text:

```bash
cutoff=$(date -d '7 days ago' +%F)
[[ 2026-10-30 < $cutoff ]] && echo "2026-10-30 is more than a week ago"
```

```text
2026-10-30 is more than a week ago
```

Outside `[[ ]]`, `<` still means "from a file", so keep this test inside the double brackets.

## Seconds since 1970: timing a job

Computers keep time as one big number: the seconds since the first moment of 1970. It's called **Unix time**, or a *timestamp*, and `date +%s` prints it. It's hard to read, but arithmetic works on it directly, so it's how a script times itself:

```bash
start=$(date +%s)
sleep 3
end=$(date +%s)
echo "That took $((end - start)) seconds"
```

```text
That took 3 seconds
```

`sleep 3` waits three seconds and stands in for a real job, such as a backup. The clock counts whole seconds, so now and then you'll see 4. A backup script can write that line to its log every night, and the day it says 400 instead of 40, you know to look.

## Check yourself

2 questions to try on the lesson page.

## So what

A date in a file name, today's date at the top of a report, "older than a week" and "how long did that take" are each one `date` command away: the pieces every scheduled script needs.

## Key terms

- [date](https://www.ask-codey.com/glossary/date)
- [Unix Time](https://www.ask-codey.com/glossary/unix-time)
- [Command Substitution](https://www.ask-codey.com/glossary/command-substitution)

## Cheat sheets

- [Dates and Times](https://www.ask-codey.com/cheat-sheets/bash-dates-cheat-sheet)

## Related

- [Values from Commands: $( ) and $(( ))](https://www.ask-codey.com/lessons/bash-command-substitution)
- [Talking to the Web: curl](https://www.ask-codey.com/lessons/bash-curl)
- [Exercise: Today's Weather Report](https://www.ask-codey.com/lessons/exercise-bash-todays-weather-report)

Source: https://www.ask-codey.com/lessons/bash-dates