Reputation: 35734

Repeat command automatically in Linux

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.

Upvotes: 349

Answers (13)

Andrew

Reputation: 3969

I created a shell alias that will watch the commands passed to it every x number of seconds. The commands can be separate arguments or separated by semicolons.

# execute commands at a specified interval of seconds
function watch.command {
  # USAGE: watch.commands [seconds] [commands...]
  # EXAMPLE: watch.command 5 date
  # EXAMPLE: watch.command 5 date echo 'ls -l' echo 'ps | grep "kubectl\\\|node\\\|npm\\\|puma"'
  # EXAMPLE: watch.command 5 'date; echo; ls -l; echo; ps | grep "kubectl\\\|node\\\|npm\\\|puma"' echo date 'echo; ls -1'
  local cmds=()
  for arg in "${@:2}"; do
    echo $arg | sed 's/; /;/g' | tr \; \\n | while read cmd; do
      cmds+=($cmd)
    done
  done
  while true; do
    clear
    for cmd in $cmds; do
      eval $cmd
    done
    sleep $1
  done
}

https://gist.github.com/Gerst20051/99c1cf570a2d0d59f09339a806732fd3

Upvotes: 0

arsdragonfly

Reputation: 76

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

Upvotes: 4

Sebastian Wagner

Reputation: 2516

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.

Upvotes: 52

Valentin Bajrami

Reputation: 229

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.

Upvotes: 4

HeadAndTail

Reputation: 812

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

Upvotes: 1

math

Reputation: 169

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.

Upvotes: 2

Ranjithkumar T

Reputation: 1956

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 & ]

Example:

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.

# ./while_check.sh &

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 &

Upvotes: 16

Eduardo

Reputation: 91

watch is good but will clean the screen.

watch -n 1 'ps aux | grep php'

Upvotes: 9

jonathanzh

Reputation: 1454

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"'

Upvotes: 21

mcote

Reputation: 644

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.

Upvotes: 6

mikhail

Reputation: 5179

"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

Upvotes: 106

Rawkode

Reputation: 22592

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

Upvotes: 602

Oleksandr Kravchuk

Reputation: 6319

while true; do
    sleep 5
    ls -l
done

Upvotes: 143

Repeat command automatically in Linux

Answers (13)

Output :-

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