Repeat command automatically in Linux

Question

Is it possible in Linux command line to have a command repeat every n seconds   Say  I have an import running  and I am doing  ls -l   to check if the file size is increasing  I would like to have a command to have this repeat automatically

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If you want to avoid  drifting   meaning you want the command to execute every N seconds regardless of how long the command takes  assuming it takes less than N seconds   here s some bash that will repeat a command every 5 seconds with one-second accuracy  and will print out a warning if it can t keep up    PERIOD 5  while   1   do     let lastup  date   s        do command     let diff  date   s - lastup     if     diff  -lt   PERIOD        then         sleep     PERIOD- diff       elif     diff  -gt   PERIOD        then         echo  Command took longer than iteration period of  PERIOD seconds       fi done   It may still drift a little since the sleep is only accurate to one second   You could improve this accuracy by creative use of the date command

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watch -n 5  ls -l   Will Runls -l command after every 5s Output  - Every 5 0s  ls -l                                                                                                      Fri Nov 17 16 28 25 2017  total 169548 -rw-rw-r--  1 sachin sachin     4292 Oct 18 12 16 About us Admission doc -rw-rw-r--  1 sachin sachin      865 Oct 13 15 26 About us At glance doc -rw-rw-r--  1 sachin sachin     1816 Oct 13 16 11 About us Principle doc -rw-rw-r--  1 sachin sachin     1775 Oct 13 15 59 About us Vission mission doc -rw-rw-r--  1 sachin sachin     1970 Oct 13 16 41 Academic Middle school doc -rw-rw-r--  1 sachin sachin      772 Oct 16 16 07 academics High School doc -rw-rw-r--  1 sachin sachin      648 Oct 16 13 34 academics pre primary doc -rw-rw-r--  1 sachin sachin      708 Oct 16 13 39 academics primary doc -rwxrwxr-x  1 sachin sachin     8816 Nov  1 12 10 a out -rw-rw-r--  1 sachin sachin    23956 Oct 23 18 14 Ass1 c   -rw-rw-r--  1 sachin sachin      342 Oct 23 22 13 Ass2 doc drwxrwxr-x  2 sachin sachin     4096 Oct 19 10 45 Backtracking drwxrwxr-x  3 sachin sachin     4096 Sep 23 20 09 BeautifulSoup drwxrwxr-x  2 sachin sachin     4096 Nov  2 00 18 CL 1 drwxrwxr-x  2 sachin sachin     4096 Oct 23 20 16 Code drwxr-xr-x  2 sachin sachin     4096 Nov 15 12 05 Desktop -rw-rw-r--  1 sachin sachin        0 Oct 13 23 12 doc drwxr-xr-x  4 sachin sachin     4096 Nov  6 21 18 Documents drwxr-xr-x 27 sachin sachin    12288 Nov 17 13 23 Downloads -rw-r--r--  1 sachin sachin     8980 Sep 19 23 58 examples desktop

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while true  do     sleep 5     ls -l done

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Running commands periodically without cron is possible when we go with while   As a command   while true   do command   sleep 100   done  amp    ex    while true   do echo  date    sleep 2   done  amp      Example    while true do echo  Hello World  sleep 100 done  amp    Do not forget the last  amp  as it will put your loop in the background  But you need to find the process id with command  ps -ef   grep your script  then you need to kill it  So kindly add the   amp   when you running the script       while check sh  amp    Here is the same loop as a script  Create file  while check sh  and put this in it      bin bash while true  do      echo  Hello World    Substitute this line for whatever command you want      sleep 100 done   Then run it by typing bash   while check sh  amp

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If you want to do something a specific number of times you can always do this   repeat 300 do my first command here  amp  amp  sleep 1 5

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You can run the following and filter the size only  If your file was called  somefilename you can do the following  while    do ls -lh   awk   some   print  5    sleep 5  done  One of the many ideas

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Watch every 5 seconds      watch -n 5 ls -l  If you wish to have visual confirmation of changes  append --differences prior to the ls command   According to the OSX man page  there s also     The --cumulative option makes highlighting  sticky   presenting a   running display of  all  positions  that  have  ever changed   The -t   or --no-title option turns off the header showing the interval    command  and current time at the top of the display  as well as the   following blank line    Linux Unix man page can be found here

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If the command contains some special characters such as pipes and quotes  the command needs to be padded with quotes  For example  to repeat ls -l   grep  txt   the watch command should be   watch -n 5  ls -l   grep  txt

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sleep already returns 0  As such  I m using   while sleep 3   do ls -l   done   This is a tiny bit shorter than mikhail s solution  A minor drawback is that it sleeps before running the target command for the first time

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To minimize drift more easily  use   while    do sleep 1m  amp  some-command  wait  done   there will still be a tiny amount of drift due to bash s time to run the loop structure and the sleep command to actually execute   hint      evals to 0 ie true

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watch  does not allow fractions of a second in Busybox  while  sleep  does  If that matters to you  try this   while true  do ls -l  sleep  5  done

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watch is good but will clean the screen   watch -n 1  ps aux   grep php

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A concise solution  which is particularly useful if you want to run the command repeatedly until it fails  and lets you see all output   while ls -l  do     sleep 5 done

[linux] Repeat command automatically in Linux

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