after

README

after

Cronjob utility to target sub-minute times

Usage

$ crontab -l
* * * * * after <duration(s)> <command [args]>

• <duration(s)> must be comma-separated list of durations, as understood by Go, at least 1ms and shorter than one minute (1m). For durations over one minute use regular Cron spec.
  • Durations can also be of the repeating form */<duration> which will repeat every <duration> within the same minute. Example: */20s will run on seconds 0, 20, and 40 of the minute.
  • Durations can be combined in a comma separated list, like: 5s,*/20s500ms,15s
• <command [args]> must be command and optional arguments to execute.
  • <command [args]> is only executed once per concurrent durations, meaning */15,*/30 will NOT run command twice at seconds 0 and 30 although both expressions coincide in those seconds.

Quoting

If command or arguments to be executed by after require quoting, please use quotes and/or escape them, like so:

$ after \*/20s sh -c "sleep 2 && echo escape\'d \$(date)"
escape'd Sat Apr 1 07:55:29 IDT 2023
escape'd Sat Apr 1 07:55:49 IDT 2023
escape'd Sat Apr 1 07:56:09 IDT 2023

See debug for more diagnostic output, for example:

$ DEBUG=1 after \*/20s sh -c "sleep 2 && echo escape\'d \$(date)"
#2023-04-01T07:53:52.599851+03:00 $ /bin/sh -c sh -c "sleep 2 && echo escape\\'d \$(date)"
#map[0s:true 20s:true 40s:true]
>>2023-04-01T07:53:52.602151+03:00|pid: 52770|cmd: /bin/sh -c sh -c "sleep 2 && echo escape\\'d \$(date)"
escape'd Sat Apr 1 07:53:54 IDT 2023
<<2023-04-01T07:53:54.627701+03:00|pid: 52770|code: 0
>>2023-04-01T07:54:12.606055+03:00|pid: 52784|cmd: /bin/sh -c sh -c "sleep 2 && echo escape\\'d \$(date)"
escape'd Sat Apr 1 07:54:14 IDT 2023
<<2023-04-01T07:54:14.631721+03:00|pid: 52784|code: 0
>>2023-04-01T07:54:32.604656+03:00|pid: 52798|cmd: /bin/sh -c sh -c "sleep 2 && echo escape\\'d \$(date)"
escape'd Sat Apr 1 07:54:34 IDT 2023
<<2023-04-01T07:54:34.635794+03:00|pid: 52798|code: 0

Standard in, out, err

• <command [args]> receives stdin, stdout and stderr from after.

Exit codes

Exit code will be exit code of <command [args]>, in addition of these cases related to after operation:

• 1 missing duration(s). No valid duration was given either first parameter missing or none of the values given is valid (comma-separated list).
• 2 missing command. Second parameter onwards must be command to execute when duration(s) expire.

Build

Requirements

• GNU make
• Golang

Binaries are built as binary ./build/<OS>-<ARCH>/after:

$ make build

Install

With ~/go/bin in your PATH simply use:

• go install github.com/dberstein/after@latest

Or alternatively use make's build infrastructure:

• Builds binary ./build/<OS>-<ARCH>/after and installs it as binary /usr[/local]/bin/after.

  $ sudo make install

Uninstall

Uninstalls binary of make install.

$ sudo make uninstall

Debug

If environmental variable DEBUG has a non-empty and different from 0 value, debug information is sent to stderr.

Information includes full command line being executed, the schedule of execution and each execution's process (pid), timestamp and exit code.

For example compare:

$ after \*/20s date +%T
07:59:45
08:00:05
08:00:25

With, where schedule of executions (0s, 20s, 40s) and each execution and its exit code are displayed in STDERR:

$ DEBUG=1 after \*/20s date +%T
#2023-04-01T07:59:45.884795+03:00 $ /bin/sh -c date +%T
#map[0s:true 20s:true 40s:true]
>>2023-04-01T07:59:45.886871+03:00|pid: 53094|cmd: /bin/sh -c date +%T
07:59:45
<<2023-04-01T07:59:45.895521+03:00|pid: 53094|code: 0
>>2023-04-01T08:00:05.892511+03:00|pid: 53105|cmd: /bin/sh -c date +%T
08:00:05
<<2023-04-01T08:00:05.906056+03:00|pid: 53105|code: 0
>>2023-04-01T08:00:25.891189+03:00|pid: 53124|cmd: /bin/sh -c date +%T
08:00:25
<<2023-04-01T08:00:25.905354+03:00|pid: 53124|code: 0

Examples

Fixed seconds

Every 15m run and log twice "date" at seconds 20 and 45 of the minute:

*/15 * * * * after 20s,45S date >> date1.log

Repeating seconds

Every 15m run and every 5 seconds and at second 33 with 500 milliseconds log "date". Note that */... as duration for after must be quoted or escaped:

*/15 * * * * after '*/5,33s500ms' date >> date2.log