How can I repeat a command every interval of time , so that it will allow me to run commands for checking or monitoring directories ?

There is no need for a script, i need just a simple command to be executed in terminal.


10 Answers 10


You can use watch command, watch is used to run any designated command at regular intervals.

Open Terminal and type:

watch -n x <your command>

change x to be the time in seconds you want.

For more help using the watch command and its options, run man watch or visit this Link.

For example : the following will list, every 60s, on the same Terminal, the contents of the Desktop directory so that you can know if any changes took place:

watch -n 60 ls -l ~/Desktop
  • 37
    +1 but be careful when using expansions. For example, try the difference between watch -n 1 'echo $COLUMNS' and watch -n 1 echo $COLUMNS when resizing your terminal - the former is expanded every second, but the latter is expanded only once before watch starts. – l0b0 Mar 6 '14 at 16:06
  • Problem I have with this solution is that you can't run watch as a process and just leave it running in the background (for example with &disown) – Cestarian May 13 '15 at 2:06
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    Is there any way to use watch with "history enabled" type command? I love using watch, but sometimes I'd prefer to see a log of previous executions as well, instead of just the last one. And yes, I know I can use scripting (while true) to accomplish this, but using the watch utilitiy is so much cleaner! – rinogo Sep 14 '15 at 18:44
  • this worked for simpler commands but with pipelined commands chaining this didn't work for me.. following was the command I tried =>cat api.log | grep 'calling' | wc -l – Sudip Bhandari Sep 29 '16 at 7:43
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    -bash: watch: command not found, macOS 10.14.1 – Abhijit Sarkar Nov 27 '18 at 4:22

You can also use this command in terminal, apart from nux's answer :

while true; do <your_command>; sleep <interval_in_seconds>; done


while true; do ls; sleep 2; done

This command will print output of ls at an interval of 2 sec.

Use Ctrl+C to stop the process.

There is few drawbacks of watch

  • It can not use any aliased commands.
  • If the output of any command is quite long, scrolling does not work properly.
  • There is some trouble to set maximum time interval beyond certain value.
  • watch will interpret ANSI color sequences passing escape characters using -c or --color option. For example output of pygmentize will work but it will fail for ls --color=auto.

In the above circumstances this may appear as a better option.

  • watch exists for that, this is a bit useless I would say – Bruno Pereira Mar 6 '14 at 16:36
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    I am not claiming this answer is to be used at first place. watch is good in most cases. That is why I mentioned "apart from nux's answer" at the beginning. But there are few problems with watch for example One can not use any aliased commands with watch. Take for example ll which is aliased to ls -laF but can not be used with watch. Also in case if the output of any command is quite long you will be in trouble in scrolling using watch. In these few special cases this answer may appear a better option. – sourav c. Mar 6 '14 at 17:25
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    while sleep x is better - it's easier to kill. – d33tah Mar 8 '14 at 15:43
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    This is a nice alternative and, unlike watch, it keeps the command history. – adelriosantiago Feb 14 '17 at 18:31
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    Another weirdness with watch is that if I resize my terminal window, it runs the command again. – Jesse Buchanan Sep 25 '19 at 20:14

Just wanted to pitch in to souravc and nux's answers:

  1. While watch will work perfectly on Ubuntu, you might want to avoid that if you want your "Unix-fu" to be pure - on FreeBSD for example, watch is a command to "snoop on another tty line".
  2. while true; do command; sleep SECONDS; done also has a caveat - your command might be harder to kill using CTR+C. You might want to prefer while sleep SECONDS; do command; done - it's not only shorter, but also easier to interrupt. The caveat is that it will first sleep, then run your command, so you'll need to wait some SECONDS before the first occurrence of the command will happen.
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    Hopefully it's acceptable as an answer instead of a comment - I wanted to show another solution here and commenting would actually give me less attention. – d33tah Mar 8 '14 at 15:52
  • Why exactly does it matter where you put sleep in the while loop? I couldn't find any difference, Ctrl+C broke the loop instantly no matter what. – dessert Nov 17 '17 at 8:03
  • @dessert: depends on what you're trying to break out from I guess. Normally, ctrl+c would just kill your command and sleep and only break if you kill true. – d33tah Dec 11 '17 at 17:08

Sounds like the ideal task for the cron daemon which allows for running periodic commands. Run the crontab -e command to start editing your user's cron configuration. Its format is documented in crontab(5). Basically you have five time-related, space-separated fields followed by a command:

The time and date fields are:

       field          allowed values
       -----          --------------
       minute         0-59
       hour           0-23
       day of month   1-31
       month          1-12 (or names, see below)
       day of week    0-7 (0 or 7 is Sunday, or use names)

For example, if you would like to run a Python script on every Tuesday, 11 AM:

0 11 * * 1 python ~/yourscript.py

There are also some special names that replace the time, like @reboot. Very helpful if you need to create a temporary directory. From my crontab (listed with crontab -l):

# Creates a temporary directory for ~/.distcc at boot
@reboot ln -sfn "$(mktemp -d "/tmp/distcc.XXXXXXXX")" "$HOME/.distcc"
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    The question asks how to run something periodically in the terminal. cron runs behind the scenes rather than in the terminal – northern-bradley Dec 15 '14 at 19:22

If you are monitoring the file system, then inotifywait is brilliant and certainly adds less load on your system.

Example :

In 1st terminal type this command :

$ inotifywait .

Then in 2nd terminal, any command that affects the current directory,

$ touch newfile

Then in original terminal inotifywait will wake up and report the event

./ CREATE newfile2

Or in a loop

$ while true ; do inotifywait . ; done
Setting up watches.  
Watches established.
./ OPEN newfile2
Setting up watches.  
Watches established.
./ OPEN newfile2
Setting up watches.  
Watches established.
./ DELETE newfile
Setting up watches.  
Watches established.
./ CREATE,ISDIR newdir
Setting up watches.  
Watches established.
  • the user told you , no script , and maybe he dont want to monitor anything – nux Mar 6 '14 at 16:36
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    I didn't tell him to write a script, I suggested that if they are looping inorder to watch for particular filesystem event, then inotifywait is useful, and uses less resources than repeating a command. I often run several commands on a command line eg grep something InALogFile|less is that a script ? – X Tian Mar 6 '14 at 16:43
  • its a good answer , try to edit it to look more simple . – nux Mar 6 '14 at 16:45
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    What could be simpler than . I can't leave out the command. – X Tian Mar 6 '14 at 16:48
  • Thanks @XTian, a great command. I also now saw in the man page that you can add -m to continually monitor without a loop. – yoniLavi Jul 21 '14 at 16:06

You can create your own repeat command doing the following steps; credits here:

First, open your .bash_aliases file:

$ xdg-open ~/.bash-aliases

Second, paste these lines at the bottom of the file and save:

repeat() {
while [ $(( n -= 1 )) -ge 0 ]

Third, either close and open again your terminal, or type:

$ source ~/.bash_aliases

Et voilà ! You can now use it like this:

$ repeat 5 echo Hello World !!!


$ repeat 5 ./myscript.sh
  • there is a small typo in the line xdg-open ~/.bash-aliases. it should be: xdg-open ~/.bash_aliases (ie: underscore) – ssinfod Feb 4 '18 at 1:21

you can use crontab. run the command crontab -e and open it with your preferred text editor, then add this line

*/10 * * * *  /path-to-your-command

This will run your command every 10 minutes

* */4 * * *  /path-to-your-command

This will run your command every 4 hours

Another possible solution

$ ..some command...; for i in $(seq X); do $cmd; sleep Y; done

X number of times to repeat.

Y time to wait to repeat.

Example :

$ echo; for i in $(seq 5); do $cmd "This is echo number: $i"; sleep 1;done
  • Why is this an improvement? You just added an extra, needless, step by saving the command as a variable. The only things this does is i) make it longer to type ii) forces you to use only simple commands, no pipes or redirects etc. – terdon Jul 3 '14 at 11:52
  • Remove the extra variable – Maythux May 14 '15 at 11:24

Another concern with the "watch" approach proposed above is that it does display the result only when the process is done. "date;sleep 58;date" will display the 2 dates only after 59 seconds... If you start something running for 4 minutes, that display slowly multiple pages of content, you will not really see it.

On the other hand, the concern with the "while" approach is that it doesn't take the task duration into consideration.

while true; do script_that_take_between_10s_to_50s.sh; sleep 50; done

With this, the script will run sometime every minutes, sometime might take 1m40. So even if a cron will be able to run it every minutes, here, it will not.

So to see the output on the shell as it's generated and wait for the exact request time, you need to look at the time before, and after, and loop with the while.

Something like:

while ( true ); do
  echo Date starting `date`
  before=`date +%s`
  sleep `echo $(( ( RANDOM % 30 )  + 1 ))`
  echo Before waiting `date`
  after=`date +%s`
  DELAY=`echo "60-($after-$before)" | bc`
  sleep $DELAY
  echo Done waiting `date`

This will output this:

As you can see, the command runs every minutes:

Date starting Mon Dec 14 15:49:34 EST 2015
Before waiting Mon Dec 14 15:49:52 EST 2015
Done waiting Mon Dec 14 15:50:34 EST 2015

Date starting Mon Dec 14 15:50:34 EST 2015
Before waiting Mon Dec 14 15:50:39 EST 2015
Done waiting Mon Dec 14 15:51:34 EST 2015

So just replace the "sleep echo $(( ( RANDOM % 30 ) + 1 ))" command with what ever you want and that will be run, on the terminal/shell, exactly every minute. If you want another schedule, just change the "60" seconds with what ever you need.

Shorter version without the debug lines:

while ( true ); do
  before=`date +%s`
  sleep `echo $(( ( RANDOM % 30 )  + 1 ))` # Place you command here
  after=`date +%s`
  DELAY=`echo "60-($after-$before)" | bc`
  sleep $DELAY
  • Replying to myself... If your command takes more than the delay you configure, $DELAY will get a negative value and the sleep command will fail so the script will restart right away. Need to be aware of that. – jmspaggi Dec 14 '15 at 21:06
while true; do <your command>; sleep <time interval>;done

In this line of code, 1. the process will run continuously as we are using a while loop, 2. then do the command execution, 3. sleep for the time interval

as an example while true; do ./git.bash;sleep 20;done this line automatically push my code to GitHub after every 20 second


Even You can use this command to repeat your command 10 times or more when it done

for i in {1..10}; do your command; done

for example:

for i in {1..10}; do speedtest; done

  • 4
    ... but there would be no x interval time which question asks. – Kulfy Jan 12 at 11:46

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