Repeat command automatically in Linux


Linux Problem Overview

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.

Linux Solutions

Solution 1 - Linux

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

Solution 2 - Linux

while true; do
    sleep 5
    ls -l

Solution 3 - Linux

"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

Solution 4 - Linux

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.

Solution 5 - Linux

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"'

Solution 6 - Linux

Running commands periodically without cron is possible when we go with while.

As a command:

while true ; do command ; sleep 100 ; done &
[ ex: # while true;  do echo `date` ; sleep 2 ; done & ]


while true
do echo "Hello World"
sleep 100
done &

Do not forget the last & 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 '&' when you running the script.

# ./ &

Here is the same loop as a script. Create file "" and put this in it:

while true; do 
    echo "Hello World" # Substitute this line for whatever command you want.
    sleep 100

Then run it by typing bash ./ &

Solution 7 - Linux

watch is good but will clean the screen.

watch -n 1 'ps aux | grep php'

Solution 8 - Linux

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):


while [ 1 ]
    let lastup=`date +%s`
    # do command
    let diff=`date +%s`-$lastup
    if [ "$diff" -lt "$PERIOD" ]
        sleep $(($PERIOD-$diff))
    elif [ "$diff" -gt "$PERIOD" ]
        echo "Command took longer than iteration period of $PERIOD seconds!"

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.

Solution 9 - Linux

If you want to do something a specific number of times you can always do this:

repeat 300 do my first command here && sleep 1.5

Solution 10 - Linux

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.

Solution 11 - Linux

To minimize drift more easily, use:

while :; do sleep 1m & 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.

Solution 12 - Linux

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

Solution 13 - Linux

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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Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionMarty WallaceView Question on Stackoverflow
Solution 1 - LinuxRawkodeView Answer on Stackoverflow
Solution 2 - LinuxOleksandr KravchukView Answer on Stackoverflow
Solution 3 - LinuxmikhailView Answer on Stackoverflow
Solution 4 - LinuxSebastian WagnerView Answer on Stackoverflow
Solution 5 - LinuxjonathanzhView Answer on Stackoverflow
Solution 6 - LinuxRanjithkumar TView Answer on Stackoverflow
Solution 7 - LinuxEduardoView Answer on Stackoverflow
Solution 8 - LinuxmcoteView Answer on Stackoverflow
Solution 9 - LinuxbrightballView Answer on Stackoverflow
Solution 10 - LinuxValentin BajramiView Answer on Stackoverflow
Solution 11 - LinuxmathView Answer on Stackoverflow
Solution 12 - LinuxarsdragonflyView Answer on Stackoverflow
Solution 13 - LinuxHeadAndTailView Answer on Stackoverflow