nodemcu-firmware/docs/modules/cron.md

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# Cron Module
| Since | Origin / Contributor | Maintainer | Source |
| :----- | :-------------------- | :---------- | :------ |
| 2016-12-18 | [PhoeniX](https://github.com/djphoenix) | [PhoeniX](https://github.com/djphoenix) | [cron.c](../../app/modules/cron.c)|
[Cron](https://en.wikipedia.org/wiki/Cron)-like scheduler module.
!!! important
This module needs RTC time to operate correctly. Do not forget to include the [`rtctime`](rtctime.md) module **and** initialize it properly.
!!! important
The cron expression has to be in GMT/UTC!
## cron.schedule()
Creates a new schedule entry.
#### Syntax
`cron.schedule(mask, callback)`
#### Parameters
- `mask` - [crontab](https://en.wikipedia.org/wiki/Cron#Overview)-like string mask for schedule
- `callback` - callback `function(entry)` that is executed at the scheduled time
#### Returns
`cron.entry` sub module
#### Example
```lua
cron.schedule("* * * * *", function(e)
print("Every minute")
end)
cron.schedule("*/5 * * * *", function(e)
print("Every 5 minutes")
end)
cron.schedule("0 */2 * * *", function(e)
print("Every 2 hours")
end)
```
## cron.reset()
Removes all scheduled entries.
#### Syntax
`cron.reset()`
#### Parameters
none
#### Returns
nil
# cron.entry Module
## cron.entry:handler()
Sets a new handler for entry.
#### Syntax
`handler(callback)`
#### Parameters
- `callback` - callback `function(entry)` that is executed at the scheduled time
#### Returns
nil
#### Example
```lua
ent = cron.schedule("* * * * *", function(e)
print("Every minute")
end)
ent:handler(function(e)
print("New handler: Every minute")
end)
```
## cron.entry:schedule()
Sets a new schedule mask.
#### Syntax
`schedule(mask)`
#### Parameters
- `mask` - [crontab](https://en.wikipedia.org/wiki/Cron#Overview)-like string mask for schedule
#### Returns
none
#### Example
```lua
ent = cron.schedule("* * * * *", function(e)
print("Tick")
end)
-- Every 5 minutes is really better!
ent:schedule("*/5 * * * *")
```
## cron.entry:unschedule()
Disables schedule.
Disabled schedules may be enabled again by calling [`:schedule(mask)`](cron.md#cronentryschedule).
#### Syntax
`unschedule()`
#### Parameters
none
#### Returns
nil
#### Example
```lua
ent = cron.schedule("* * * * *", function(e)
print("Tick")
end)
-- We don't need this anymore
ent:unschedule()
```