Shell: is it possible to delay a command without using `sleep`?












20















Are there any substitutes, alternatives or bash tricks for delaying commands without using sleep? For example, performing the below command without actually using sleep:



$ sleep 10 && echo "This is a test"





linux bash shell-script shell sleep







share|improve this question




















  • 41





    What's wrong with sleep?

    – muru
    Nov 19 '18 at 10:55






  • 5





    There's no real reason other than curiosity. I thought it would be interesting to learn some alternative solutions. I think at might be one, but I couldn't find any usage examples.

    – user321697
    Nov 19 '18 at 11:11






  • 1





    @user321697 “at” is to schedule single jobs. they are executed by the atd service, so they won’t pause your shell script. one use case for at would be to have it do something at a specified time (async) and create a marker file when it’s finished, while your script is waiting for that file to appear in a while loop. you could achieve a similar effect by scheduling a job to send your script a SIGCONT and then freezing your script by sending yourself a SIGSTOP.

    – Grega Bremec
    Nov 19 '18 at 11:13








  • 1





    I came here expecting everyone to suggest a spinlock. I'm pleasantly surprised by all the answers.

    – Daan van Hoek
    Nov 19 '18 at 15:59






  • 3





    Re: "Curiosity" -- in unix.stackexchange.com/help/dont-ask, note the requirement that "You should only ask practical, answerable questions based on actual problems that you face." -- that this has been well-received despite controvening that guideline makes it a rather rare exception.

    – Charles Duffy
    Nov 21 '18 at 1:02


















20















Are there any substitutes, alternatives or bash tricks for delaying commands without using sleep? For example, performing the below command without actually using sleep:



$ sleep 10 && echo "This is a test"





linux bash shell-script shell sleep







share|improve this question




















  • 41





    What's wrong with sleep?

    – muru
    Nov 19 '18 at 10:55






  • 5





    There's no real reason other than curiosity. I thought it would be interesting to learn some alternative solutions. I think at might be one, but I couldn't find any usage examples.

    – user321697
    Nov 19 '18 at 11:11






  • 1





    @user321697 “at” is to schedule single jobs. they are executed by the atd service, so they won’t pause your shell script. one use case for at would be to have it do something at a specified time (async) and create a marker file when it’s finished, while your script is waiting for that file to appear in a while loop. you could achieve a similar effect by scheduling a job to send your script a SIGCONT and then freezing your script by sending yourself a SIGSTOP.

    – Grega Bremec
    Nov 19 '18 at 11:13








  • 1





    I came here expecting everyone to suggest a spinlock. I'm pleasantly surprised by all the answers.

    – Daan van Hoek
    Nov 19 '18 at 15:59






  • 3





    Re: "Curiosity" -- in unix.stackexchange.com/help/dont-ask, note the requirement that "You should only ask practical, answerable questions based on actual problems that you face." -- that this has been well-received despite controvening that guideline makes it a rather rare exception.

    – Charles Duffy
    Nov 21 '18 at 1:02
















20












20








20


4






Are there any substitutes, alternatives or bash tricks for delaying commands without using sleep? For example, performing the below command without actually using sleep:



$ sleep 10 && echo "This is a test"





linux bash shell-script shell sleep







share|improve this question
















Are there any substitutes, alternatives or bash tricks for delaying commands without using sleep? For example, performing the below command without actually using sleep:



$ sleep 10 && echo "This is a test"





linux bash shell-script shell sleep




linux bash shell-script shell sleep






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 19 '18 at 11:36









Fabby

3,86811229




3,86811229










asked Nov 19 '18 at 10:52









user321697user321697

11414




11414








  • 41





    What's wrong with sleep?

    – muru
    Nov 19 '18 at 10:55






  • 5





    There's no real reason other than curiosity. I thought it would be interesting to learn some alternative solutions. I think at might be one, but I couldn't find any usage examples.

    – user321697
    Nov 19 '18 at 11:11






  • 1





    @user321697 “at” is to schedule single jobs. they are executed by the atd service, so they won’t pause your shell script. one use case for at would be to have it do something at a specified time (async) and create a marker file when it’s finished, while your script is waiting for that file to appear in a while loop. you could achieve a similar effect by scheduling a job to send your script a SIGCONT and then freezing your script by sending yourself a SIGSTOP.

    – Grega Bremec
    Nov 19 '18 at 11:13








  • 1





    I came here expecting everyone to suggest a spinlock. I'm pleasantly surprised by all the answers.

    – Daan van Hoek
    Nov 19 '18 at 15:59






  • 3





    Re: "Curiosity" -- in unix.stackexchange.com/help/dont-ask, note the requirement that "You should only ask practical, answerable questions based on actual problems that you face." -- that this has been well-received despite controvening that guideline makes it a rather rare exception.

    – Charles Duffy
    Nov 21 '18 at 1:02
















  • 41





    What's wrong with sleep?

    – muru
    Nov 19 '18 at 10:55






  • 5





    There's no real reason other than curiosity. I thought it would be interesting to learn some alternative solutions. I think at might be one, but I couldn't find any usage examples.

    – user321697
    Nov 19 '18 at 11:11






  • 1





    @user321697 “at” is to schedule single jobs. they are executed by the atd service, so they won’t pause your shell script. one use case for at would be to have it do something at a specified time (async) and create a marker file when it’s finished, while your script is waiting for that file to appear in a while loop. you could achieve a similar effect by scheduling a job to send your script a SIGCONT and then freezing your script by sending yourself a SIGSTOP.

    – Grega Bremec
    Nov 19 '18 at 11:13








  • 1





    I came here expecting everyone to suggest a spinlock. I'm pleasantly surprised by all the answers.

    – Daan van Hoek
    Nov 19 '18 at 15:59






  • 3





    Re: "Curiosity" -- in unix.stackexchange.com/help/dont-ask, note the requirement that "You should only ask practical, answerable questions based on actual problems that you face." -- that this has been well-received despite controvening that guideline makes it a rather rare exception.

    – Charles Duffy
    Nov 21 '18 at 1:02










41




41





What's wrong with sleep?

– muru
Nov 19 '18 at 10:55





What's wrong with sleep?

– muru
Nov 19 '18 at 10:55




5




5





There's no real reason other than curiosity. I thought it would be interesting to learn some alternative solutions. I think at might be one, but I couldn't find any usage examples.

– user321697
Nov 19 '18 at 11:11





There's no real reason other than curiosity. I thought it would be interesting to learn some alternative solutions. I think at might be one, but I couldn't find any usage examples.

– user321697
Nov 19 '18 at 11:11




1




1





@user321697 “at” is to schedule single jobs. they are executed by the atd service, so they won’t pause your shell script. one use case for at would be to have it do something at a specified time (async) and create a marker file when it’s finished, while your script is waiting for that file to appear in a while loop. you could achieve a similar effect by scheduling a job to send your script a SIGCONT and then freezing your script by sending yourself a SIGSTOP.

– Grega Bremec
Nov 19 '18 at 11:13







@user321697 “at” is to schedule single jobs. they are executed by the atd service, so they won’t pause your shell script. one use case for at would be to have it do something at a specified time (async) and create a marker file when it’s finished, while your script is waiting for that file to appear in a while loop. you could achieve a similar effect by scheduling a job to send your script a SIGCONT and then freezing your script by sending yourself a SIGSTOP.

– Grega Bremec
Nov 19 '18 at 11:13






1




1





I came here expecting everyone to suggest a spinlock. I'm pleasantly surprised by all the answers.

– Daan van Hoek
Nov 19 '18 at 15:59





I came here expecting everyone to suggest a spinlock. I'm pleasantly surprised by all the answers.

– Daan van Hoek
Nov 19 '18 at 15:59




3




3





Re: "Curiosity" -- in unix.stackexchange.com/help/dont-ask, note the requirement that "You should only ask practical, answerable questions based on actual problems that you face." -- that this has been well-received despite controvening that guideline makes it a rather rare exception.

– Charles Duffy
Nov 21 '18 at 1:02







Re: "Curiosity" -- in unix.stackexchange.com/help/dont-ask, note the requirement that "You should only ask practical, answerable questions based on actual problems that you face." -- that this has been well-received despite controvening that guideline makes it a rather rare exception.

– Charles Duffy
Nov 21 '18 at 1:02












10 Answers
10






active

oldest

votes


















16














You have alternatives to sleep: They are at and cron. Contrary to sleep these need you to provide the time at which you need them to run.




  • Make sure the atd service is running by executing service atd status.

    Now let's say the date is 11:17 am UTC; if you need to execute a command at 11:25 UTC, the syntax is: echo "This is a test" | at 11:25.

    Now keep in mind that atd by default will not be logging the completion of the jobs. For more refer this link. It's better that your application has its own logging.


  • You can schedule jobs in cron, for more refer : man cron to see its options or crontab -e to add new jobs. /var/log/cron can be checked for the info on execution on jobs.



FYI sleep system call suspends the current execution and schedules it w.r.t. the argument passed to it.



EDIT:



As @Gaius mentioned , you can also add minutes time to at command.But lets say time is 12:30:30 and now you ran the scheduler with now +1 minutes. Even though 1 minute, which translates to 60 seconds was specified , the at doesn't really wait till 12:31:30 to execute the job, rather it executes the job at 12:31:00. The time-units can be minutes, hours, days, or weeks. For more refer man at



e.g: echo "ls" | at now +1 minutes






share|improve this answer





















  • 6





    This is not true, you can schedule an at job for say now +1 minute, to run in a minutes time

    – Gaius
    Nov 19 '18 at 16:48



















28














With bash builtins, you can do:



coproc read -t 10 && wait "$!" || true


To sleep for 10 seconds without using sleep. The coproc is to make so that read's stdin is a pipe where nothing will ever come out from. || true is because wait's exit status will reflect a SIGALRM delivery which would cause the shell to exit if the errexit option is set.



In other shells:



mksh and ksh93 have sleep built-in, no point in using anything else there (though they both also support read -t).



zsh also supports read -t, but also has a builtin wrapper around select(), so you can also use:



zmodload zsh/zselect

zselect -t 1000 # centiseconds


If what you want is schedule things to be run from an interactive shell session, see also the zsh/sched module in zsh.






share|improve this answer


























  • Would you consider read -t 10 < /dev/zero || true ?

    – Jeff Schaller
    Nov 19 '18 at 14:22








  • 5





    @JeffSchaller I would avoid it as that's a busy loop.

    – Stéphane Chazelas
    Nov 19 '18 at 14:23











  • @StéphaneChazelas I wouldn't expect that to be a busy loop – I'd expect any shell's read to be implemented using select(2) or something similar (implying that read-with-timeout would be a good answer to this question). I'm expressing surprise rather than contradicting you, but can you point to further discussion of this?

    – Norman Gray
    Nov 19 '18 at 15:41






  • 5





    @NormanGray, /dev/zero is a file that contains an infinite amount of data (NUL bytes). So read will read as much as it can during those 10 seconds. Thankfully, in the case of bash which doesn't support storing NUL bytes in its variables, that won't use up any memory, but that will still hog CPU resources.

    – Stéphane Chazelas
    Nov 19 '18 at 15:44






  • 1





    @NormanGray, if run from a terminal, /dev/stdout would be the tty device, so it would have side effects (like stopping the script if run in background) and would return if the user presses enter for instance. read -t 10 /dev/stdout | : would work on Linux, but on Linux only, while coproc should work regardless of the OS.

    – Stéphane Chazelas
    Nov 19 '18 at 16:10





















6














Since there are answers which are suggesting to use the non-standard -t delay option of read, here is a way to do a timed-out read in a standard shell:



{ ss=`stty -g`; stty -icanon min 0 time 20; read foo; stty "$ss"; }


The argument to stty time is in tenths of second.






share|improve this answer































    5














    Using the bash built-in variable $SECONDS and a busy-loop:



    for((target=$((SECONDS + 10)); SECONDS < target; true)); do :; done





    share|improve this answer



















    • 2





      That would in effect pause for a duration ranging somewhere in between 9 and 10 seconds though (due to a bug in bash; zsh and mksh had similar issues but have been fixed since)

      – Stéphane Chazelas
      Nov 19 '18 at 14:05








    • 7





      A good way to make heat.

      – ctrl-alt-delor
      Nov 19 '18 at 14:50






    • 6





      won't be the first time I'm accused of being full of hot air! :)

      – Jeff Schaller
      Nov 19 '18 at 14:51



















    5














    Some other ideas.



    top -d10 -n2 >/dev/null
    

    
vmstat 10 2 >/dev/null
    

    
sar 10 1 >/dev/null
    

    
timeout 10s tail -f /dev/null





    share|improve this answer



















    • 1





      You "stole" my idea of timelimit/timeout.... +1

      – Rui F Ribeiro
      Nov 20 '18 at 11:36





















    4














    Back in the days of microcomputers running BASIC, delays were usually accomplished with an empty loop:



    FOR I = 1 TO 10000:NEXT



    The same principle could be used to insert a delay in a shell script:



    COUNTER=0; while [ $COUNTER -lt 10000 ]; do :; let COUNTER=COUNTER+1; done



    Of course, the problem with this approach is that the length of the delay will vary from machine to machine according to its processor speed (or even on the same machine under different loads). Unlike sleep, it will probably also max out your CPU (or one of its cores).






    share|improve this answer



















    • 2





      A good way to make heat.

      – ctrl-alt-delor
      Nov 19 '18 at 14:50






    • 2





      Delay-loops are a terrible idea for anything except the very shortest of sleeps (a couple nanoseconds or clock cycles in a device driver) on any modern CPU that can run a Unix-like OS. i.e. a sleep so short you can't usefully have the CPU do anything else while waiting, like schedule another process or enter a low-power sleep state before waking on a timer interrupt. Dynamic CPU-frequency makes it impossible to even calibrate a delay loop for counts per second, except as a minimum delay potentially sleeping a lot longer at low clock speeds before ramping up.

      – Peter Cordes
      Nov 19 '18 at 22:43











    • Ancient computers had a power consumption that was much less dependent on workload. Modern CPUs need to dynamically power down different parts of the chip as much as possible to not melt (e.g. power down parts of the FPU or SIMD execution units while only integer code is running, or at least gate the clock signal to parts of the chip that don't need to be switching). And entering a low-power sleep state when idle (instead of spinning in an infinite loop waiting for timer interrupts) is also more recent than the ancient computers you mention.

      – Peter Cordes
      Nov 19 '18 at 22:46











    • For more about CPU history, see Modern Microprocessors A 90-Minute Guide! - lighterra.com/papers/modernmicroprocessors.

      – Peter Cordes
      Nov 19 '18 at 22:47



















    3














    the oldest trick in the book:



    read && echo "This is a test"


    Just hit Enter and it'll continue!






    share|improve this answer
























    • This wont if the process needs to be run interaction free or in the background right?

      – sai sasanka
      Nov 19 '18 at 11:30











    • Correct: But that was not one of the OP's requirements as per the original question, so still a valid answer... ;-) >:-)

      – Fabby
      Nov 20 '18 at 11:30






    • 1





      OP specifically gives an example (with sleep) and asks for an equivalent alternative without. So read doesn't parse, sorry. ;)

      – AnoE
      Nov 20 '18 at 12:58











    • @AnoE Stéphane's answer is of course the best, mine is just the oldest --- press «enter» to continue --- ;-)

      – Fabby
      Nov 20 '18 at 18:00



















    3














    There is no built-in, that does the same as sleep (unless sleep is built-in). However there are some other commands that will wait.



    A few include.




    • at and cron: used to schedule tasks at a specific time.


    • inotifywait: used to wait for a file, or files to be modified/removed/added/etc







    share|improve this answer


























    • Thanks for this. Could you provide an example for performing a scheduled task (10 seconds from now) with at?

      – user321697
      Nov 19 '18 at 11:23






    • 1





      an edit and an upvote! ;-)

      – Fabby
      Nov 19 '18 at 11:23











    • cron store tasks in crontab, right? Where does at store the scheduled data?

      – user321697
      Nov 19 '18 at 11:25











    • @user321697 Already answered here

      – Fabby
      Nov 19 '18 at 11:26











    • Sorry for reverting back your edit to the Q: you changed the OPs question's main purpose which would invalidate the simplest answer of all... ¯_(ツ)_/¯

      – Fabby
      Nov 19 '18 at 11:38





















    3














    A classic from the Land of Windows and Batches:



    ping -c 11 localhost >/dev/null && echo "This is a test"





    share|improve this answer
























    • Firewall or name system misconfiguration might introduce a significant additional delay tough.

      – spectras
      Nov 20 '18 at 12:21






    • 1





      127.0.0.1 ... @spectras

      – AnoE
      Nov 20 '18 at 12:59






    • 1





      Thankfully no longer needed, as Windows now supports sleep natively.

      – Baldrickk
      Nov 20 '18 at 13:26






    • 1





      @AnoE> solves the name system part, not the firewall part. Though not common, it can be configured to silently drop pings on local interface. That will cause ping to wait much longer.

      – spectras
      Nov 21 '18 at 1:42











    • +1 for the "fond" memories

      – A C
      Nov 21 '18 at 6:26



















    0














    If you want to interactively wait for a new line in a file, then 


    tail -f
    .

    Waiting for a change on a filesystem? Then use e.g. 


    inotify / inoticoming
    .

    And there are other options, depending on what you mean with "wait".






    share|improve this answer























      Your Answer








      StackExchange.ready(function() {
      var channelOptions = {
      tags: "".split(" "),
      id: "106"
      };
      initTagRenderer("".split(" "), "".split(" "), channelOptions);

      StackExchange.using("externalEditor", function() {
      // Have to fire editor after snippets, if snippets enabled
      if (StackExchange.settings.snippets.snippetsEnabled) {
      StackExchange.using("snippets", function() {
      createEditor();
      });
      }
      else {
      createEditor();
      }
      });

      function createEditor() {
      StackExchange.prepareEditor({
      heartbeatType: 'answer',
      autoActivateHeartbeat: false,
      convertImagesToLinks: false,
      noModals: true,
      showLowRepImageUploadWarning: true,
      reputationToPostImages: null,
      bindNavPrevention: true,
      postfix: "",
      imageUploader: {
      brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
      contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
      allowUrls: true
      },
      onDemand: true,
      discardSelector: ".discard-answer"
      ,immediatelyShowMarkdownHelp:true
      });


      }
      });














      draft saved

      draft discarded


















      StackExchange.ready(
      function () {
      StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f482725%2fshell-is-it-possible-to-delay-a-command-without-using-sleep%23new-answer', 'question_page');
      }
      );

      Post as a guest















      Required, but never shown

























      10 Answers
      10






      active

      oldest

      votes








      10 Answers
      10






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      16














      You have alternatives to sleep: They are at and cron. Contrary to sleep these need you to provide the time at which you need them to run.




      • Make sure the atd service is running by executing service atd status.

        Now let's say the date is 11:17 am UTC; if you need to execute a command at 11:25 UTC, the syntax is: echo "This is a test" | at 11:25.

        Now keep in mind that atd by default will not be logging the completion of the jobs. For more refer this link. It's better that your application has its own logging.


      • You can schedule jobs in cron, for more refer : man cron to see its options or crontab -e to add new jobs. /var/log/cron can be checked for the info on execution on jobs.



      FYI sleep system call suspends the current execution and schedules it w.r.t. the argument passed to it.



      EDIT:



      As @Gaius mentioned , you can also add minutes time to at command.But lets say time is 12:30:30 and now you ran the scheduler with now +1 minutes. Even though 1 minute, which translates to 60 seconds was specified , the at doesn't really wait till 12:31:30 to execute the job, rather it executes the job at 12:31:00. The time-units can be minutes, hours, days, or weeks. For more refer man at



      e.g: echo "ls" | at now +1 minutes






      share|improve this answer





















      • 6





        This is not true, you can schedule an at job for say now +1 minute, to run in a minutes time

        – Gaius
        Nov 19 '18 at 16:48
















      16














      You have alternatives to sleep: They are at and cron. Contrary to sleep these need you to provide the time at which you need them to run.




      • Make sure the atd service is running by executing service atd status.

        Now let's say the date is 11:17 am UTC; if you need to execute a command at 11:25 UTC, the syntax is: echo "This is a test" | at 11:25.

        Now keep in mind that atd by default will not be logging the completion of the jobs. For more refer this link. It's better that your application has its own logging.


      • You can schedule jobs in cron, for more refer : man cron to see its options or crontab -e to add new jobs. /var/log/cron can be checked for the info on execution on jobs.



      FYI sleep system call suspends the current execution and schedules it w.r.t. the argument passed to it.



      EDIT:



      As @Gaius mentioned , you can also add minutes time to at command.But lets say time is 12:30:30 and now you ran the scheduler with now +1 minutes. Even though 1 minute, which translates to 60 seconds was specified , the at doesn't really wait till 12:31:30 to execute the job, rather it executes the job at 12:31:00. The time-units can be minutes, hours, days, or weeks. For more refer man at



      e.g: echo "ls" | at now +1 minutes






      share|improve this answer





















      • 6





        This is not true, you can schedule an at job for say now +1 minute, to run in a minutes time

        – Gaius
        Nov 19 '18 at 16:48














      16












      16








      16







      You have alternatives to sleep: They are at and cron. Contrary to sleep these need you to provide the time at which you need them to run.




      • Make sure the atd service is running by executing service atd status.

        Now let's say the date is 11:17 am UTC; if you need to execute a command at 11:25 UTC, the syntax is: echo "This is a test" | at 11:25.

        Now keep in mind that atd by default will not be logging the completion of the jobs. For more refer this link. It's better that your application has its own logging.


      • You can schedule jobs in cron, for more refer : man cron to see its options or crontab -e to add new jobs. /var/log/cron can be checked for the info on execution on jobs.



      FYI sleep system call suspends the current execution and schedules it w.r.t. the argument passed to it.



      EDIT:



      As @Gaius mentioned , you can also add minutes time to at command.But lets say time is 12:30:30 and now you ran the scheduler with now +1 minutes. Even though 1 minute, which translates to 60 seconds was specified , the at doesn't really wait till 12:31:30 to execute the job, rather it executes the job at 12:31:00. The time-units can be minutes, hours, days, or weeks. For more refer man at



      e.g: echo "ls" | at now +1 minutes






      share|improve this answer















      You have alternatives to sleep: They are at and cron. Contrary to sleep these need you to provide the time at which you need them to run.




      • Make sure the atd service is running by executing service atd status.

        Now let's say the date is 11:17 am UTC; if you need to execute a command at 11:25 UTC, the syntax is: echo "This is a test" | at 11:25.

        Now keep in mind that atd by default will not be logging the completion of the jobs. For more refer this link. It's better that your application has its own logging.


      • You can schedule jobs in cron, for more refer : man cron to see its options or crontab -e to add new jobs. /var/log/cron can be checked for the info on execution on jobs.



      FYI sleep system call suspends the current execution and schedules it w.r.t. the argument passed to it.



      EDIT:



      As @Gaius mentioned , you can also add minutes time to at command.But lets say time is 12:30:30 and now you ran the scheduler with now +1 minutes. Even though 1 minute, which translates to 60 seconds was specified , the at doesn't really wait till 12:31:30 to execute the job, rather it executes the job at 12:31:00. The time-units can be minutes, hours, days, or weeks. For more refer man at



      e.g: echo "ls" | at now +1 minutes







      share|improve this answer














      share|improve this answer



      share|improve this answer








      edited Nov 19 '18 at 17:22

























      answered Nov 19 '18 at 11:28









      sai sasankasai sasanka

      754110




      754110








      • 6





        This is not true, you can schedule an at job for say now +1 minute, to run in a minutes time

        – Gaius
        Nov 19 '18 at 16:48














      • 6





        This is not true, you can schedule an at job for say now +1 minute, to run in a minutes time

        – Gaius
        Nov 19 '18 at 16:48








      6




      6





      This is not true, you can schedule an at job for say now +1 minute, to run in a minutes time

      – Gaius
      Nov 19 '18 at 16:48





      This is not true, you can schedule an at job for say now +1 minute, to run in a minutes time

      – Gaius
      Nov 19 '18 at 16:48













      28














      With bash builtins, you can do:



      coproc read -t 10 && wait "$!" || true


      To sleep for 10 seconds without using sleep. The coproc is to make so that read's stdin is a pipe where nothing will ever come out from. || true is because wait's exit status will reflect a SIGALRM delivery which would cause the shell to exit if the errexit option is set.



      In other shells:



      mksh and ksh93 have sleep built-in, no point in using anything else there (though they both also support read -t).



      zsh also supports read -t, but also has a builtin wrapper around select(), so you can also use:



      zmodload zsh/zselect
      
zselect -t 1000 # centiseconds


      If what you want is schedule things to be run from an interactive shell session, see also the zsh/sched module in zsh.






      share|improve this answer


























      • Would you consider read -t 10 < /dev/zero || true ?

        – Jeff Schaller
        Nov 19 '18 at 14:22








      • 5





        @JeffSchaller I would avoid it as that's a busy loop.

        – Stéphane Chazelas
        Nov 19 '18 at 14:23











      • @StéphaneChazelas I wouldn't expect that to be a busy loop – I'd expect any shell's read to be implemented using select(2) or something similar (implying that read-with-timeout would be a good answer to this question). I'm expressing surprise rather than contradicting you, but can you point to further discussion of this?

        – Norman Gray
        Nov 19 '18 at 15:41






      • 5





        @NormanGray, /dev/zero is a file that contains an infinite amount of data (NUL bytes). So read will read as much as it can during those 10 seconds. Thankfully, in the case of bash which doesn't support storing NUL bytes in its variables, that won't use up any memory, but that will still hog CPU resources.

        – Stéphane Chazelas
        Nov 19 '18 at 15:44






      • 1





        @NormanGray, if run from a terminal, /dev/stdout would be the tty device, so it would have side effects (like stopping the script if run in background) and would return if the user presses enter for instance. read -t 10 /dev/stdout | : would work on Linux, but on Linux only, while coproc should work regardless of the OS.

        – Stéphane Chazelas
        Nov 19 '18 at 16:10


















      28














      With bash builtins, you can do:



      coproc read -t 10 && wait "$!" || true


      To sleep for 10 seconds without using sleep. The coproc is to make so that read's stdin is a pipe where nothing will ever come out from. || true is because wait's exit status will reflect a SIGALRM delivery which would cause the shell to exit if the errexit option is set.



      In other shells:



      mksh and ksh93 have sleep built-in, no point in using anything else there (though they both also support read -t).



      zsh also supports read -t, but also has a builtin wrapper around select(), so you can also use:



      zmodload zsh/zselect
      
zselect -t 1000 # centiseconds


      If what you want is schedule things to be run from an interactive shell session, see also the zsh/sched module in zsh.






      share|improve this answer


























      • Would you consider read -t 10 < /dev/zero || true ?

        – Jeff Schaller
        Nov 19 '18 at 14:22








      • 5





        @JeffSchaller I would avoid it as that's a busy loop.

        – Stéphane Chazelas
        Nov 19 '18 at 14:23











      • @StéphaneChazelas I wouldn't expect that to be a busy loop – I'd expect any shell's read to be implemented using select(2) or something similar (implying that read-with-timeout would be a good answer to this question). I'm expressing surprise rather than contradicting you, but can you point to further discussion of this?

        – Norman Gray
        Nov 19 '18 at 15:41






      • 5





        @NormanGray, /dev/zero is a file that contains an infinite amount of data (NUL bytes). So read will read as much as it can during those 10 seconds. Thankfully, in the case of bash which doesn't support storing NUL bytes in its variables, that won't use up any memory, but that will still hog CPU resources.

        – Stéphane Chazelas
        Nov 19 '18 at 15:44






      • 1





        @NormanGray, if run from a terminal, /dev/stdout would be the tty device, so it would have side effects (like stopping the script if run in background) and would return if the user presses enter for instance. read -t 10 /dev/stdout | : would work on Linux, but on Linux only, while coproc should work regardless of the OS.

        – Stéphane Chazelas
        Nov 19 '18 at 16:10
















      28












      28








      28







      With bash builtins, you can do:



      coproc read -t 10 && wait "$!" || true


      To sleep for 10 seconds without using sleep. The coproc is to make so that read's stdin is a pipe where nothing will ever come out from. || true is because wait's exit status will reflect a SIGALRM delivery which would cause the shell to exit if the errexit option is set.



      In other shells:



      mksh and ksh93 have sleep built-in, no point in using anything else there (though they both also support read -t).



      zsh also supports read -t, but also has a builtin wrapper around select(), so you can also use:



      zmodload zsh/zselect
      
zselect -t 1000 # centiseconds


      If what you want is schedule things to be run from an interactive shell session, see also the zsh/sched module in zsh.






      share|improve this answer















      With bash builtins, you can do:



      coproc read -t 10 && wait "$!" || true


      To sleep for 10 seconds without using sleep. The coproc is to make so that read's stdin is a pipe where nothing will ever come out from. || true is because wait's exit status will reflect a SIGALRM delivery which would cause the shell to exit if the errexit option is set.



      In other shells:



      mksh and ksh93 have sleep built-in, no point in using anything else there (though they both also support read -t).



      zsh also supports read -t, but also has a builtin wrapper around select(), so you can also use:



      zmodload zsh/zselect
      
zselect -t 1000 # centiseconds


      If what you want is schedule things to be run from an interactive shell session, see also the zsh/sched module in zsh.







      share|improve this answer














      share|improve this answer



      share|improve this answer








      edited Nov 19 '18 at 12:28

























      answered Nov 19 '18 at 11:27









      Stéphane ChazelasStéphane Chazelas

      303k57570926




      303k57570926













      • Would you consider read -t 10 < /dev/zero || true ?

        – Jeff Schaller
        Nov 19 '18 at 14:22








      • 5





        @JeffSchaller I would avoid it as that's a busy loop.

        – Stéphane Chazelas
        Nov 19 '18 at 14:23











      • @StéphaneChazelas I wouldn't expect that to be a busy loop – I'd expect any shell's read to be implemented using select(2) or something similar (implying that read-with-timeout would be a good answer to this question). I'm expressing surprise rather than contradicting you, but can you point to further discussion of this?

        – Norman Gray
        Nov 19 '18 at 15:41






      • 5





        @NormanGray, /dev/zero is a file that contains an infinite amount of data (NUL bytes). So read will read as much as it can during those 10 seconds. Thankfully, in the case of bash which doesn't support storing NUL bytes in its variables, that won't use up any memory, but that will still hog CPU resources.

        – Stéphane Chazelas
        Nov 19 '18 at 15:44






      • 1





        @NormanGray, if run from a terminal, /dev/stdout would be the tty device, so it would have side effects (like stopping the script if run in background) and would return if the user presses enter for instance. read -t 10 /dev/stdout | : would work on Linux, but on Linux only, while coproc should work regardless of the OS.

        – Stéphane Chazelas
        Nov 19 '18 at 16:10





















      • Would you consider read -t 10 < /dev/zero || true ?

        – Jeff Schaller
        Nov 19 '18 at 14:22








      • 5





        @JeffSchaller I would avoid it as that's a busy loop.

        – Stéphane Chazelas
        Nov 19 '18 at 14:23











      • @StéphaneChazelas I wouldn't expect that to be a busy loop – I'd expect any shell's read to be implemented using select(2) or something similar (implying that read-with-timeout would be a good answer to this question). I'm expressing surprise rather than contradicting you, but can you point to further discussion of this?

        – Norman Gray
        Nov 19 '18 at 15:41






      • 5





        @NormanGray, /dev/zero is a file that contains an infinite amount of data (NUL bytes). So read will read as much as it can during those 10 seconds. Thankfully, in the case of bash which doesn't support storing NUL bytes in its variables, that won't use up any memory, but that will still hog CPU resources.

        – Stéphane Chazelas
        Nov 19 '18 at 15:44






      • 1





        @NormanGray, if run from a terminal, /dev/stdout would be the tty device, so it would have side effects (like stopping the script if run in background) and would return if the user presses enter for instance. read -t 10 /dev/stdout | : would work on Linux, but on Linux only, while coproc should work regardless of the OS.

        – Stéphane Chazelas
        Nov 19 '18 at 16:10



















      Would you consider read -t 10 < /dev/zero || true ?

      – Jeff Schaller
      Nov 19 '18 at 14:22







      Would you consider read -t 10 < /dev/zero || true ?

      – Jeff Schaller
      Nov 19 '18 at 14:22






      5




      5





      @JeffSchaller I would avoid it as that's a busy loop.

      – Stéphane Chazelas
      Nov 19 '18 at 14:23





      @JeffSchaller I would avoid it as that's a busy loop.

      – Stéphane Chazelas
      Nov 19 '18 at 14:23













      @StéphaneChazelas I wouldn't expect that to be a busy loop – I'd expect any shell's read to be implemented using select(2) or something similar (implying that read-with-timeout would be a good answer to this question). I'm expressing surprise rather than contradicting you, but can you point to further discussion of this?

      – Norman Gray
      Nov 19 '18 at 15:41





      @StéphaneChazelas I wouldn't expect that to be a busy loop – I'd expect any shell's read to be implemented using select(2) or something similar (implying that read-with-timeout would be a good answer to this question). I'm expressing surprise rather than contradicting you, but can you point to further discussion of this?

      – Norman Gray
      Nov 19 '18 at 15:41




      5




      5





      @NormanGray, /dev/zero is a file that contains an infinite amount of data (NUL bytes). So read will read as much as it can during those 10 seconds. Thankfully, in the case of bash which doesn't support storing NUL bytes in its variables, that won't use up any memory, but that will still hog CPU resources.

      – Stéphane Chazelas
      Nov 19 '18 at 15:44





      @NormanGray, /dev/zero is a file that contains an infinite amount of data (NUL bytes). So read will read as much as it can during those 10 seconds. Thankfully, in the case of bash which doesn't support storing NUL bytes in its variables, that won't use up any memory, but that will still hog CPU resources.

      – Stéphane Chazelas
      Nov 19 '18 at 15:44




      1




      1





      @NormanGray, if run from a terminal, /dev/stdout would be the tty device, so it would have side effects (like stopping the script if run in background) and would return if the user presses enter for instance. read -t 10 /dev/stdout | : would work on Linux, but on Linux only, while coproc should work regardless of the OS.

      – Stéphane Chazelas
      Nov 19 '18 at 16:10







      @NormanGray, if run from a terminal, /dev/stdout would be the tty device, so it would have side effects (like stopping the script if run in background) and would return if the user presses enter for instance. read -t 10 /dev/stdout | : would work on Linux, but on Linux only, while coproc should work regardless of the OS.

      – Stéphane Chazelas
      Nov 19 '18 at 16:10













      6














      Since there are answers which are suggesting to use the non-standard -t delay option of read, here is a way to do a timed-out read in a standard shell:



      { ss=`stty -g`; stty -icanon min 0 time 20; read foo; stty "$ss"; }


      The argument to stty time is in tenths of second.






      share|improve this answer




























        6














        Since there are answers which are suggesting to use the non-standard -t delay option of read, here is a way to do a timed-out read in a standard shell:



        { ss=`stty -g`; stty -icanon min 0 time 20; read foo; stty "$ss"; }


        The argument to stty time is in tenths of second.






        share|improve this answer


























          6












          6








          6







          Since there are answers which are suggesting to use the non-standard -t delay option of read, here is a way to do a timed-out read in a standard shell:



          { ss=`stty -g`; stty -icanon min 0 time 20; read foo; stty "$ss"; }


          The argument to stty time is in tenths of second.






          share|improve this answer













          Since there are answers which are suggesting to use the non-standard -t delay option of read, here is a way to do a timed-out read in a standard shell:



          { ss=`stty -g`; stty -icanon min 0 time 20; read foo; stty "$ss"; }


          The argument to stty time is in tenths of second.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Nov 19 '18 at 17:26









          mosvymosvy

          7,1491427




          7,1491427























              5














              Using the bash built-in variable $SECONDS and a busy-loop:



              for((target=$((SECONDS + 10)); SECONDS < target; true)); do :; done





              share|improve this answer



















              • 2





                That would in effect pause for a duration ranging somewhere in between 9 and 10 seconds though (due to a bug in bash; zsh and mksh had similar issues but have been fixed since)

                – Stéphane Chazelas
                Nov 19 '18 at 14:05








              • 7





                A good way to make heat.

                – ctrl-alt-delor
                Nov 19 '18 at 14:50






              • 6





                won't be the first time I'm accused of being full of hot air! :)

                – Jeff Schaller
                Nov 19 '18 at 14:51
















              5














              Using the bash built-in variable $SECONDS and a busy-loop:



              for((target=$((SECONDS + 10)); SECONDS < target; true)); do :; done





              share|improve this answer



















              • 2





                That would in effect pause for a duration ranging somewhere in between 9 and 10 seconds though (due to a bug in bash; zsh and mksh had similar issues but have been fixed since)

                – Stéphane Chazelas
                Nov 19 '18 at 14:05








              • 7





                A good way to make heat.

                – ctrl-alt-delor
                Nov 19 '18 at 14:50






              • 6





                won't be the first time I'm accused of being full of hot air! :)

                – Jeff Schaller
                Nov 19 '18 at 14:51














              5












              5








              5







              Using the bash built-in variable $SECONDS and a busy-loop:



              for((target=$((SECONDS + 10)); SECONDS < target; true)); do :; done





              share|improve this answer













              Using the bash built-in variable $SECONDS and a busy-loop:



              for((target=$((SECONDS + 10)); SECONDS < target; true)); do :; done






              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered Nov 19 '18 at 13:33









              Jeff SchallerJeff Schaller

              40.8k1056129




              40.8k1056129








              • 2





                That would in effect pause for a duration ranging somewhere in between 9 and 10 seconds though (due to a bug in bash; zsh and mksh had similar issues but have been fixed since)

                – Stéphane Chazelas
                Nov 19 '18 at 14:05








              • 7





                A good way to make heat.

                – ctrl-alt-delor
                Nov 19 '18 at 14:50






              • 6





                won't be the first time I'm accused of being full of hot air! :)

                – Jeff Schaller
                Nov 19 '18 at 14:51














              • 2





                That would in effect pause for a duration ranging somewhere in between 9 and 10 seconds though (due to a bug in bash; zsh and mksh had similar issues but have been fixed since)

                – Stéphane Chazelas
                Nov 19 '18 at 14:05








              • 7





                A good way to make heat.

                – ctrl-alt-delor
                Nov 19 '18 at 14:50






              • 6





                won't be the first time I'm accused of being full of hot air! :)

                – Jeff Schaller
                Nov 19 '18 at 14:51








              2




              2





              That would in effect pause for a duration ranging somewhere in between 9 and 10 seconds though (due to a bug in bash; zsh and mksh had similar issues but have been fixed since)

              – Stéphane Chazelas
              Nov 19 '18 at 14:05







              That would in effect pause for a duration ranging somewhere in between 9 and 10 seconds though (due to a bug in bash; zsh and mksh had similar issues but have been fixed since)

              – Stéphane Chazelas
              Nov 19 '18 at 14:05






              7




              7





              A good way to make heat.

              – ctrl-alt-delor
              Nov 19 '18 at 14:50





              A good way to make heat.

              – ctrl-alt-delor
              Nov 19 '18 at 14:50




              6




              6





              won't be the first time I'm accused of being full of hot air! :)

              – Jeff Schaller
              Nov 19 '18 at 14:51





              won't be the first time I'm accused of being full of hot air! :)

              – Jeff Schaller
              Nov 19 '18 at 14:51











              5














              Some other ideas.



              top -d10 -n2 >/dev/null
              

              
vmstat 10 2 >/dev/null
              

              
sar 10 1 >/dev/null
              

              
timeout 10s tail -f /dev/null





              share|improve this answer



















              • 1





                You "stole" my idea of timelimit/timeout.... +1

                – Rui F Ribeiro
                Nov 20 '18 at 11:36


















              5














              Some other ideas.



              top -d10 -n2 >/dev/null
              

              
vmstat 10 2 >/dev/null
              

              
sar 10 1 >/dev/null
              

              
timeout 10s tail -f /dev/null





              share|improve this answer



















              • 1





                You "stole" my idea of timelimit/timeout.... +1

                – Rui F Ribeiro
                Nov 20 '18 at 11:36
















              5












              5








              5







              Some other ideas.



              top -d10 -n2 >/dev/null
              

              
vmstat 10 2 >/dev/null
              

              
sar 10 1 >/dev/null
              

              
timeout 10s tail -f /dev/null





              share|improve this answer













              Some other ideas.



              top -d10 -n2 >/dev/null
              

              
vmstat 10 2 >/dev/null
              

              
sar 10 1 >/dev/null
              

              
timeout 10s tail -f /dev/null






              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered Nov 19 '18 at 22:25









              stevesteve

              14k22452




              14k22452








              • 1





                You "stole" my idea of timelimit/timeout.... +1

                – Rui F Ribeiro
                Nov 20 '18 at 11:36
















              • 1





                You "stole" my idea of timelimit/timeout.... +1

                – Rui F Ribeiro
                Nov 20 '18 at 11:36










              1




              1





              You "stole" my idea of timelimit/timeout.... +1

              – Rui F Ribeiro
              Nov 20 '18 at 11:36







              You "stole" my idea of timelimit/timeout.... +1

              – Rui F Ribeiro
              Nov 20 '18 at 11:36













              4














              Back in the days of microcomputers running BASIC, delays were usually accomplished with an empty loop:



              FOR I = 1 TO 10000:NEXT



              The same principle could be used to insert a delay in a shell script:



              COUNTER=0; while [ $COUNTER -lt 10000 ]; do :; let COUNTER=COUNTER+1; done



              Of course, the problem with this approach is that the length of the delay will vary from machine to machine according to its processor speed (or even on the same machine under different loads). Unlike sleep, it will probably also max out your CPU (or one of its cores).






              share|improve this answer



















              • 2





                A good way to make heat.

                – ctrl-alt-delor
                Nov 19 '18 at 14:50






              • 2





                Delay-loops are a terrible idea for anything except the very shortest of sleeps (a couple nanoseconds or clock cycles in a device driver) on any modern CPU that can run a Unix-like OS. i.e. a sleep so short you can't usefully have the CPU do anything else while waiting, like schedule another process or enter a low-power sleep state before waking on a timer interrupt. Dynamic CPU-frequency makes it impossible to even calibrate a delay loop for counts per second, except as a minimum delay potentially sleeping a lot longer at low clock speeds before ramping up.

                – Peter Cordes
                Nov 19 '18 at 22:43











              • Ancient computers had a power consumption that was much less dependent on workload. Modern CPUs need to dynamically power down different parts of the chip as much as possible to not melt (e.g. power down parts of the FPU or SIMD execution units while only integer code is running, or at least gate the clock signal to parts of the chip that don't need to be switching). And entering a low-power sleep state when idle (instead of spinning in an infinite loop waiting for timer interrupts) is also more recent than the ancient computers you mention.

                – Peter Cordes
                Nov 19 '18 at 22:46











              • For more about CPU history, see Modern Microprocessors A 90-Minute Guide! - lighterra.com/papers/modernmicroprocessors.

                – Peter Cordes
                Nov 19 '18 at 22:47
















              4














              Back in the days of microcomputers running BASIC, delays were usually accomplished with an empty loop:



              FOR I = 1 TO 10000:NEXT



              The same principle could be used to insert a delay in a shell script:



              COUNTER=0; while [ $COUNTER -lt 10000 ]; do :; let COUNTER=COUNTER+1; done



              Of course, the problem with this approach is that the length of the delay will vary from machine to machine according to its processor speed (or even on the same machine under different loads). Unlike sleep, it will probably also max out your CPU (or one of its cores).






              share|improve this answer



















              • 2





                A good way to make heat.

                – ctrl-alt-delor
                Nov 19 '18 at 14:50






              • 2





                Delay-loops are a terrible idea for anything except the very shortest of sleeps (a couple nanoseconds or clock cycles in a device driver) on any modern CPU that can run a Unix-like OS. i.e. a sleep so short you can't usefully have the CPU do anything else while waiting, like schedule another process or enter a low-power sleep state before waking on a timer interrupt. Dynamic CPU-frequency makes it impossible to even calibrate a delay loop for counts per second, except as a minimum delay potentially sleeping a lot longer at low clock speeds before ramping up.

                – Peter Cordes
                Nov 19 '18 at 22:43











              • Ancient computers had a power consumption that was much less dependent on workload. Modern CPUs need to dynamically power down different parts of the chip as much as possible to not melt (e.g. power down parts of the FPU or SIMD execution units while only integer code is running, or at least gate the clock signal to parts of the chip that don't need to be switching). And entering a low-power sleep state when idle (instead of spinning in an infinite loop waiting for timer interrupts) is also more recent than the ancient computers you mention.

                – Peter Cordes
                Nov 19 '18 at 22:46











              • For more about CPU history, see Modern Microprocessors A 90-Minute Guide! - lighterra.com/papers/modernmicroprocessors.

                – Peter Cordes
                Nov 19 '18 at 22:47














              4












              4








              4







              Back in the days of microcomputers running BASIC, delays were usually accomplished with an empty loop:



              FOR I = 1 TO 10000:NEXT



              The same principle could be used to insert a delay in a shell script:



              COUNTER=0; while [ $COUNTER -lt 10000 ]; do :; let COUNTER=COUNTER+1; done



              Of course, the problem with this approach is that the length of the delay will vary from machine to machine according to its processor speed (or even on the same machine under different loads). Unlike sleep, it will probably also max out your CPU (or one of its cores).






              share|improve this answer













              Back in the days of microcomputers running BASIC, delays were usually accomplished with an empty loop:



              FOR I = 1 TO 10000:NEXT



              The same principle could be used to insert a delay in a shell script:



              COUNTER=0; while [ $COUNTER -lt 10000 ]; do :; let COUNTER=COUNTER+1; done



              Of course, the problem with this approach is that the length of the delay will vary from machine to machine according to its processor speed (or even on the same machine under different loads). Unlike sleep, it will probably also max out your CPU (or one of its cores).







              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered Nov 19 '18 at 12:42









              PsychonautPsychonaut

              339212




              339212








              • 2





                A good way to make heat.

                – ctrl-alt-delor
                Nov 19 '18 at 14:50






              • 2





                Delay-loops are a terrible idea for anything except the very shortest of sleeps (a couple nanoseconds or clock cycles in a device driver) on any modern CPU that can run a Unix-like OS. i.e. a sleep so short you can't usefully have the CPU do anything else while waiting, like schedule another process or enter a low-power sleep state before waking on a timer interrupt. Dynamic CPU-frequency makes it impossible to even calibrate a delay loop for counts per second, except as a minimum delay potentially sleeping a lot longer at low clock speeds before ramping up.

                – Peter Cordes
                Nov 19 '18 at 22:43











              • Ancient computers had a power consumption that was much less dependent on workload. Modern CPUs need to dynamically power down different parts of the chip as much as possible to not melt (e.g. power down parts of the FPU or SIMD execution units while only integer code is running, or at least gate the clock signal to parts of the chip that don't need to be switching). And entering a low-power sleep state when idle (instead of spinning in an infinite loop waiting for timer interrupts) is also more recent than the ancient computers you mention.

                – Peter Cordes
                Nov 19 '18 at 22:46











              • For more about CPU history, see Modern Microprocessors A 90-Minute Guide! - lighterra.com/papers/modernmicroprocessors.

                – Peter Cordes
                Nov 19 '18 at 22:47














              • 2





                A good way to make heat.

                – ctrl-alt-delor
                Nov 19 '18 at 14:50






              • 2





                Delay-loops are a terrible idea for anything except the very shortest of sleeps (a couple nanoseconds or clock cycles in a device driver) on any modern CPU that can run a Unix-like OS. i.e. a sleep so short you can't usefully have the CPU do anything else while waiting, like schedule another process or enter a low-power sleep state before waking on a timer interrupt. Dynamic CPU-frequency makes it impossible to even calibrate a delay loop for counts per second, except as a minimum delay potentially sleeping a lot longer at low clock speeds before ramping up.

                – Peter Cordes
                Nov 19 '18 at 22:43











              • Ancient computers had a power consumption that was much less dependent on workload. Modern CPUs need to dynamically power down different parts of the chip as much as possible to not melt (e.g. power down parts of the FPU or SIMD execution units while only integer code is running, or at least gate the clock signal to parts of the chip that don't need to be switching). And entering a low-power sleep state when idle (instead of spinning in an infinite loop waiting for timer interrupts) is also more recent than the ancient computers you mention.

                – Peter Cordes
                Nov 19 '18 at 22:46











              • For more about CPU history, see Modern Microprocessors A 90-Minute Guide! - lighterra.com/papers/modernmicroprocessors.

                – Peter Cordes
                Nov 19 '18 at 22:47








              2




              2





              A good way to make heat.

              – ctrl-alt-delor
              Nov 19 '18 at 14:50





              A good way to make heat.

              – ctrl-alt-delor
              Nov 19 '18 at 14:50




              2




              2





              Delay-loops are a terrible idea for anything except the very shortest of sleeps (a couple nanoseconds or clock cycles in a device driver) on any modern CPU that can run a Unix-like OS. i.e. a sleep so short you can't usefully have the CPU do anything else while waiting, like schedule another process or enter a low-power sleep state before waking on a timer interrupt. Dynamic CPU-frequency makes it impossible to even calibrate a delay loop for counts per second, except as a minimum delay potentially sleeping a lot longer at low clock speeds before ramping up.

              – Peter Cordes
              Nov 19 '18 at 22:43





              Delay-loops are a terrible idea for anything except the very shortest of sleeps (a couple nanoseconds or clock cycles in a device driver) on any modern CPU that can run a Unix-like OS. i.e. a sleep so short you can't usefully have the CPU do anything else while waiting, like schedule another process or enter a low-power sleep state before waking on a timer interrupt. Dynamic CPU-frequency makes it impossible to even calibrate a delay loop for counts per second, except as a minimum delay potentially sleeping a lot longer at low clock speeds before ramping up.

              – Peter Cordes
              Nov 19 '18 at 22:43













              Ancient computers had a power consumption that was much less dependent on workload. Modern CPUs need to dynamically power down different parts of the chip as much as possible to not melt (e.g. power down parts of the FPU or SIMD execution units while only integer code is running, or at least gate the clock signal to parts of the chip that don't need to be switching). And entering a low-power sleep state when idle (instead of spinning in an infinite loop waiting for timer interrupts) is also more recent than the ancient computers you mention.

              – Peter Cordes
              Nov 19 '18 at 22:46





              Ancient computers had a power consumption that was much less dependent on workload. Modern CPUs need to dynamically power down different parts of the chip as much as possible to not melt (e.g. power down parts of the FPU or SIMD execution units while only integer code is running, or at least gate the clock signal to parts of the chip that don't need to be switching). And entering a low-power sleep state when idle (instead of spinning in an infinite loop waiting for timer interrupts) is also more recent than the ancient computers you mention.

              – Peter Cordes
              Nov 19 '18 at 22:46













              For more about CPU history, see Modern Microprocessors A 90-Minute Guide! - lighterra.com/papers/modernmicroprocessors.

              – Peter Cordes
              Nov 19 '18 at 22:47





              For more about CPU history, see Modern Microprocessors A 90-Minute Guide! - lighterra.com/papers/modernmicroprocessors.

              – Peter Cordes
              Nov 19 '18 at 22:47











              3














              the oldest trick in the book:



              read && echo "This is a test"


              Just hit Enter and it'll continue!






              share|improve this answer
























              • This wont if the process needs to be run interaction free or in the background right?

                – sai sasanka
                Nov 19 '18 at 11:30











              • Correct: But that was not one of the OP's requirements as per the original question, so still a valid answer... ;-) >:-)

                – Fabby
                Nov 20 '18 at 11:30






              • 1





                OP specifically gives an example (with sleep) and asks for an equivalent alternative without. So read doesn't parse, sorry. ;)

                – AnoE
                Nov 20 '18 at 12:58











              • @AnoE Stéphane's answer is of course the best, mine is just the oldest --- press «enter» to continue --- ;-)

                – Fabby
                Nov 20 '18 at 18:00
















              3














              the oldest trick in the book:



              read && echo "This is a test"


              Just hit Enter and it'll continue!






              share|improve this answer
























              • This wont if the process needs to be run interaction free or in the background right?

                – sai sasanka
                Nov 19 '18 at 11:30











              • Correct: But that was not one of the OP's requirements as per the original question, so still a valid answer... ;-) >:-)

                – Fabby
                Nov 20 '18 at 11:30






              • 1





                OP specifically gives an example (with sleep) and asks for an equivalent alternative without. So read doesn't parse, sorry. ;)

                – AnoE
                Nov 20 '18 at 12:58











              • @AnoE Stéphane's answer is of course the best, mine is just the oldest --- press «enter» to continue --- ;-)

                – Fabby
                Nov 20 '18 at 18:00














              3












              3








              3







              the oldest trick in the book:



              read && echo "This is a test"


              Just hit Enter and it'll continue!






              share|improve this answer













              the oldest trick in the book:



              read && echo "This is a test"


              Just hit Enter and it'll continue!







              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered Nov 19 '18 at 11:21









              FabbyFabby

              3,86811229




              3,86811229













              • This wont if the process needs to be run interaction free or in the background right?

                – sai sasanka
                Nov 19 '18 at 11:30











              • Correct: But that was not one of the OP's requirements as per the original question, so still a valid answer... ;-) >:-)

                – Fabby
                Nov 20 '18 at 11:30






              • 1





                OP specifically gives an example (with sleep) and asks for an equivalent alternative without. So read doesn't parse, sorry. ;)

                – AnoE
                Nov 20 '18 at 12:58











              • @AnoE Stéphane's answer is of course the best, mine is just the oldest --- press «enter» to continue --- ;-)

                – Fabby
                Nov 20 '18 at 18:00



















              • This wont if the process needs to be run interaction free or in the background right?

                – sai sasanka
                Nov 19 '18 at 11:30











              • Correct: But that was not one of the OP's requirements as per the original question, so still a valid answer... ;-) >:-)

                – Fabby
                Nov 20 '18 at 11:30






              • 1





                OP specifically gives an example (with sleep) and asks for an equivalent alternative without. So read doesn't parse, sorry. ;)

                – AnoE
                Nov 20 '18 at 12:58











              • @AnoE Stéphane's answer is of course the best, mine is just the oldest --- press «enter» to continue --- ;-)

                – Fabby
                Nov 20 '18 at 18:00

















              This wont if the process needs to be run interaction free or in the background right?

              – sai sasanka
              Nov 19 '18 at 11:30





              This wont if the process needs to be run interaction free or in the background right?

              – sai sasanka
              Nov 19 '18 at 11:30













              Correct: But that was not one of the OP's requirements as per the original question, so still a valid answer... ;-) >:-)

              – Fabby
              Nov 20 '18 at 11:30





              Correct: But that was not one of the OP's requirements as per the original question, so still a valid answer... ;-) >:-)

              – Fabby
              Nov 20 '18 at 11:30




              1




              1





              OP specifically gives an example (with sleep) and asks for an equivalent alternative without. So read doesn't parse, sorry. ;)

              – AnoE
              Nov 20 '18 at 12:58





              OP specifically gives an example (with sleep) and asks for an equivalent alternative without. So read doesn't parse, sorry. ;)

              – AnoE
              Nov 20 '18 at 12:58













              @AnoE Stéphane's answer is of course the best, mine is just the oldest --- press «enter» to continue --- ;-)

              – Fabby
              Nov 20 '18 at 18:00





              @AnoE Stéphane's answer is of course the best, mine is just the oldest --- press «enter» to continue --- ;-)

              – Fabby
              Nov 20 '18 at 18:00











              3














              There is no built-in, that does the same as sleep (unless sleep is built-in). However there are some other commands that will wait.



              A few include.




              • at and cron: used to schedule tasks at a specific time.


              • inotifywait: used to wait for a file, or files to be modified/removed/added/etc







              share|improve this answer


























              • Thanks for this. Could you provide an example for performing a scheduled task (10 seconds from now) with at?

                – user321697
                Nov 19 '18 at 11:23






              • 1





                an edit and an upvote! ;-)

                – Fabby
                Nov 19 '18 at 11:23











              • cron store tasks in crontab, right? Where does at store the scheduled data?

                – user321697
                Nov 19 '18 at 11:25











              • @user321697 Already answered here

                – Fabby
                Nov 19 '18 at 11:26











              • Sorry for reverting back your edit to the Q: you changed the OPs question's main purpose which would invalidate the simplest answer of all... ¯_(ツ)_/¯

                – Fabby
                Nov 19 '18 at 11:38


















              3














              There is no built-in, that does the same as sleep (unless sleep is built-in). However there are some other commands that will wait.



              A few include.




              • at and cron: used to schedule tasks at a specific time.


              • inotifywait: used to wait for a file, or files to be modified/removed/added/etc







              share|improve this answer


























              • Thanks for this. Could you provide an example for performing a scheduled task (10 seconds from now) with at?

                – user321697
                Nov 19 '18 at 11:23






              • 1





                an edit and an upvote! ;-)

                – Fabby
                Nov 19 '18 at 11:23











              • cron store tasks in crontab, right? Where does at store the scheduled data?

                – user321697
                Nov 19 '18 at 11:25











              • @user321697 Already answered here

                – Fabby
                Nov 19 '18 at 11:26











              • Sorry for reverting back your edit to the Q: you changed the OPs question's main purpose which would invalidate the simplest answer of all... ¯_(ツ)_/¯

                – Fabby
                Nov 19 '18 at 11:38
















              3












              3








              3







              There is no built-in, that does the same as sleep (unless sleep is built-in). However there are some other commands that will wait.



              A few include.




              • at and cron: used to schedule tasks at a specific time.


              • inotifywait: used to wait for a file, or files to be modified/removed/added/etc







              share|improve this answer















              There is no built-in, that does the same as sleep (unless sleep is built-in). However there are some other commands that will wait.



              A few include.




              • at and cron: used to schedule tasks at a specific time.


              • inotifywait: used to wait for a file, or files to be modified/removed/added/etc








              share|improve this answer














              share|improve this answer



              share|improve this answer








              edited Nov 19 '18 at 11:23









              Fabby

              3,86811229




              3,86811229










              answered Nov 19 '18 at 11:20









              ctrl-alt-delorctrl-alt-delor

              11.2k42058




              11.2k42058













              • Thanks for this. Could you provide an example for performing a scheduled task (10 seconds from now) with at?

                – user321697
                Nov 19 '18 at 11:23






              • 1





                an edit and an upvote! ;-)

                – Fabby
                Nov 19 '18 at 11:23











              • cron store tasks in crontab, right? Where does at store the scheduled data?

                – user321697
                Nov 19 '18 at 11:25











              • @user321697 Already answered here

                – Fabby
                Nov 19 '18 at 11:26











              • Sorry for reverting back your edit to the Q: you changed the OPs question's main purpose which would invalidate the simplest answer of all... ¯_(ツ)_/¯

                – Fabby
                Nov 19 '18 at 11:38





















              • Thanks for this. Could you provide an example for performing a scheduled task (10 seconds from now) with at?

                – user321697
                Nov 19 '18 at 11:23






              • 1





                an edit and an upvote! ;-)

                – Fabby
                Nov 19 '18 at 11:23











              • cron store tasks in crontab, right? Where does at store the scheduled data?

                – user321697
                Nov 19 '18 at 11:25











              • @user321697 Already answered here

                – Fabby
                Nov 19 '18 at 11:26











              • Sorry for reverting back your edit to the Q: you changed the OPs question's main purpose which would invalidate the simplest answer of all... ¯_(ツ)_/¯

                – Fabby
                Nov 19 '18 at 11:38



















              Thanks for this. Could you provide an example for performing a scheduled task (10 seconds from now) with at?

              – user321697
              Nov 19 '18 at 11:23





              Thanks for this. Could you provide an example for performing a scheduled task (10 seconds from now) with at?

              – user321697
              Nov 19 '18 at 11:23




              1




              1





              an edit and an upvote! ;-)

              – Fabby
              Nov 19 '18 at 11:23





              an edit and an upvote! ;-)

              – Fabby
              Nov 19 '18 at 11:23













              cron store tasks in crontab, right? Where does at store the scheduled data?

              – user321697
              Nov 19 '18 at 11:25





              cron store tasks in crontab, right? Where does at store the scheduled data?

              – user321697
              Nov 19 '18 at 11:25













              @user321697 Already answered here

              – Fabby
              Nov 19 '18 at 11:26





              @user321697 Already answered here

              – Fabby
              Nov 19 '18 at 11:26













              Sorry for reverting back your edit to the Q: you changed the OPs question's main purpose which would invalidate the simplest answer of all... ¯_(ツ)_/¯

              – Fabby
              Nov 19 '18 at 11:38







              Sorry for reverting back your edit to the Q: you changed the OPs question's main purpose which would invalidate the simplest answer of all... ¯_(ツ)_/¯

              – Fabby
              Nov 19 '18 at 11:38













              3














              A classic from the Land of Windows and Batches:



              ping -c 11 localhost >/dev/null && echo "This is a test"





              share|improve this answer
























              • Firewall or name system misconfiguration might introduce a significant additional delay tough.

                – spectras
                Nov 20 '18 at 12:21






              • 1





                127.0.0.1 ... @spectras

                – AnoE
                Nov 20 '18 at 12:59






              • 1





                Thankfully no longer needed, as Windows now supports sleep natively.

                – Baldrickk
                Nov 20 '18 at 13:26






              • 1





                @AnoE> solves the name system part, not the firewall part. Though not common, it can be configured to silently drop pings on local interface. That will cause ping to wait much longer.

                – spectras
                Nov 21 '18 at 1:42











              • +1 for the "fond" memories

                – A C
                Nov 21 '18 at 6:26
















              3














              A classic from the Land of Windows and Batches:



              ping -c 11 localhost >/dev/null && echo "This is a test"





              share|improve this answer
























              • Firewall or name system misconfiguration might introduce a significant additional delay tough.

                – spectras
                Nov 20 '18 at 12:21






              • 1





                127.0.0.1 ... @spectras

                – AnoE
                Nov 20 '18 at 12:59






              • 1





                Thankfully no longer needed, as Windows now supports sleep natively.

                – Baldrickk
                Nov 20 '18 at 13:26






              • 1





                @AnoE> solves the name system part, not the firewall part. Though not common, it can be configured to silently drop pings on local interface. That will cause ping to wait much longer.

                – spectras
                Nov 21 '18 at 1:42











              • +1 for the "fond" memories

                – A C
                Nov 21 '18 at 6:26














              3












              3








              3







              A classic from the Land of Windows and Batches:



              ping -c 11 localhost >/dev/null && echo "This is a test"





              share|improve this answer













              A classic from the Land of Windows and Batches:



              ping -c 11 localhost >/dev/null && echo "This is a test"






              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered Nov 20 '18 at 8:35









              Joker_vDJoker_vD

              1311




              1311













              • Firewall or name system misconfiguration might introduce a significant additional delay tough.

                – spectras
                Nov 20 '18 at 12:21






              • 1





                127.0.0.1 ... @spectras

                – AnoE
                Nov 20 '18 at 12:59






              • 1





                Thankfully no longer needed, as Windows now supports sleep natively.

                – Baldrickk
                Nov 20 '18 at 13:26






              • 1





                @AnoE> solves the name system part, not the firewall part. Though not common, it can be configured to silently drop pings on local interface. That will cause ping to wait much longer.

                – spectras
                Nov 21 '18 at 1:42











              • +1 for the "fond" memories

                – A C
                Nov 21 '18 at 6:26



















              • Firewall or name system misconfiguration might introduce a significant additional delay tough.

                – spectras
                Nov 20 '18 at 12:21






              • 1





                127.0.0.1 ... @spectras

                – AnoE
                Nov 20 '18 at 12:59






              • 1





                Thankfully no longer needed, as Windows now supports sleep natively.

                – Baldrickk
                Nov 20 '18 at 13:26






              • 1





                @AnoE> solves the name system part, not the firewall part. Though not common, it can be configured to silently drop pings on local interface. That will cause ping to wait much longer.

                – spectras
                Nov 21 '18 at 1:42











              • +1 for the "fond" memories

                – A C
                Nov 21 '18 at 6:26

















              Firewall or name system misconfiguration might introduce a significant additional delay tough.

              – spectras
              Nov 20 '18 at 12:21





              Firewall or name system misconfiguration might introduce a significant additional delay tough.

              – spectras
              Nov 20 '18 at 12:21




              1




              1





              127.0.0.1 ... @spectras

              – AnoE
              Nov 20 '18 at 12:59





              127.0.0.1 ... @spectras

              – AnoE
              Nov 20 '18 at 12:59




              1




              1





              Thankfully no longer needed, as Windows now supports sleep natively.

              – Baldrickk
              Nov 20 '18 at 13:26





              Thankfully no longer needed, as Windows now supports sleep natively.

              – Baldrickk
              Nov 20 '18 at 13:26




              1




              1





              @AnoE> solves the name system part, not the firewall part. Though not common, it can be configured to silently drop pings on local interface. That will cause ping to wait much longer.

              – spectras
              Nov 21 '18 at 1:42





              @AnoE> solves the name system part, not the firewall part. Though not common, it can be configured to silently drop pings on local interface. That will cause ping to wait much longer.

              – spectras
              Nov 21 '18 at 1:42













              +1 for the "fond" memories

              – A C
              Nov 21 '18 at 6:26





              +1 for the "fond" memories

              – A C
              Nov 21 '18 at 6:26











              0














              If you want to interactively wait for a new line in a file, then 


              tail -f
              .

              Waiting for a change on a filesystem? Then use e.g. 


              inotify / inoticoming
              .

              And there are other options, depending on what you mean with "wait".






              share|improve this answer




























                0














                If you want to interactively wait for a new line in a file, then 


                tail -f
                .

                Waiting for a change on a filesystem? Then use e.g. 


                inotify / inoticoming
                .

                And there are other options, depending on what you mean with "wait".






                share|improve this answer


























                  0












                  0








                  0







                  If you want to interactively wait for a new line in a file, then 


                  tail -f
                  .

                  Waiting for a change on a filesystem? Then use e.g. 


                  inotify / inoticoming
                  .

                  And there are other options, depending on what you mean with "wait".






                  share|improve this answer













                  If you want to interactively wait for a new line in a file, then 


                  tail -f
                  .

                  Waiting for a change on a filesystem? Then use e.g. 


                  inotify / inoticoming
                  .

                  And there are other options, depending on what you mean with "wait".







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Nov 21 '18 at 15:35









                  EdheldilEdheldil

                  60534




                  60534






























                      draft saved

                      draft discarded




















































                      Thanks for contributing an answer to Unix & Linux Stack Exchange!


                      • Please be sure to answer the question. Provide details and share your research!

                      But avoid …



                      • Asking for help, clarification, or responding to other answers.

                      • Making statements based on opinion; back them up with references or personal experience.


                      To learn more, see our tips on writing great answers.




                      draft saved


                      draft discarded














                      StackExchange.ready(
                      function () {
                      StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f482725%2fshell-is-it-possible-to-delay-a-command-without-using-sleep%23new-answer', 'question_page');
                      }
                      );

                      Post as a guest















                      Required, but never shown





















































                      Required, but never shown














                      Required, but never shown












                      Required, but never shown







                      Required, but never shown

































                      Required, but never shown














                      Required, but never shown












                      Required, but never shown







                      Required, but never shown







                      -

                      Popular posts from this blog

                      Guess what letter conforming each word

                      Image
                      6 $begingroup$ This is an entry in the Fortnightly Topic Challenge #41: Short and Sweet. 1 letter only could be mean anything . With an additional letter in front , could be used as medicine component and something you definitely learn or at least heard once. Add another letter in front , you would possibly hear that many times . Add an additional letter in front , you would found an independent country . With an additional letter, in the end , you would found something related to apple . Add another letter in the end , you would found something bad . Hint: Each letter is unique . word knowledge letters chemistry share | improve this question ...
                      Read more

                      Port of Spain

                      Image
                      For ports in the country of Spain, see List of ports in Spain. City in City of Port of Spain, Trinidad and Tobago Port of Spain City City of Port of Spain Top to bottom (left to right): Skyline of Port of Spain from Gulf of Paria; National Academy for the Performing Arts, Independence Square, Eric Williams Plaza; MovieTowne, Port of Port of Spain Motto(s):  "We Gather Strength As We Go Along" Port of Spain Coordinates: 10°40′N 61°31′W  /  10.667°N 61.517°W  / 10.667; -61.517 Coordinates: 10°40′N 61°31′W  /  10.667°N 61.517°W  / 10.667; -61.517 Country   Trinidad and Tobago Jurisdiction City of Port of Spain Settled 1560 Incorporated (town) 1853 Incorporated (city) 1914 Government  • Mayor Joel Martinez  • Governing body City Corporation Area [1]  • City 12 km 2 (5 sq mi) Elevation [2] 66 m (217 ft) Population (2011) [1]  • City 37,074  • Rank 3rd  • Density 3,090/km 2 (8,000/sq mi)...
                      Read more

                      Run scheduled task as local user group (not BUILTIN)

                      Image
                      0 I am trying to run a scheduled task with User Group (not a single user). This is working fine when I in the field "when running a task, use the following user account:" insert BUILTIN User Group (for example: Administrators or Users). But when I try it with the created Local User Group (example: TestGroup) it is not working. The Users in the TestGroup are the same as in the Administrators group. What could be the problem? Are there some restrictions to the Created User Group compared to BUILTINUsers? scheduled-tasks taskscheduler windowstaskschedule share | improve this question asked Nov 15 '18 at 15:36 Far...
                      Read more