Execute command after seconds (without sleep)

command lineshellsleep

How can I run a command after X seconds without sleep. Or with sleep but without the shell just wait for the response of that command?

I used this but it didn't work

sleep 5 ; ls > a.txt

I need to run it in background. I try not to have to run it in a script
I try to run ls after 5 seconds, and shell does not just wait for the end of the sleep

Best Answer

A more concise way of writing what Hennes suggested is

(sleep 5; echo foo) &

Alternatively, if you need more than a few seconds, you could use at. There are three ways of giving a command to at:

  1. Pipe it:

    $ echo "ls > a.txt" | at now + 1 min
warning: commands will be executed using /bin/sh
job 3 at Thu Apr  4 20:16:00 2013

  2. Save the command you want to run in a text file, and then pass that file to at:

    $ echo "ls > a.txt" > cmd.txt
$ at now + 1 min < cmd.txt
warning: commands will be executed using /bin/sh
job 3 at Thu Apr  4 20:16:00 2013

  3. You can also pass at commands from STDIN:

    $ at now + 1 min
warning: commands will be executed using /bin/sh
at> ls

    Then, press CtrlD to exit the at shell. The ls command will be run in one minute.

You can give very precise times in the format of [[CC]YY]MMDDhhmm[.ss], as in 

$ at -t 201412182134.12 < script.sh

This will run the script script.sh at 21:34 and 12 seconds on the 18th of December 2014. So, in theory, you could use at to run something five seconds in the future. However, that is kinda like using a tank to swat a fly, and Hennes's suggestion is better.

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