How do I sleep for a millisecond in bash or ksh

Question

sleep is a very popular command and we can start sleep from 1 second:

# wait one second please 
sleep 1

but what the alternative if I need to wait only 0.1 second or between 0.1 to 1 second ?

• remark: on linux or OS X sleep 0.XXX works fine , but on solaris sleep 0.1 or sleep 0.01 - illegal syntax

Solution 1

Bash has a "loadable" sleep which supports fractional seconds, and eliminates overheads of an external command:

$ cd bash-3.2.48/examples/loadables
$ make sleep && mv sleep sleep.so
$ enable -f sleep.so sleep

Then:

$ which sleep
/usr/bin/sleep
$ builtin sleep
sleep: usage: sleep seconds[.fraction]
$ time (for f in `seq 1 10`; do builtin sleep 0.1; done)
real    0m1.000s
user    0m0.004s
sys     0m0.004s

The downside is that the loadables may not be provided with your bash binary, so you would need to compile them yourself as shown (though on Solaris it would not necessarily be as simple as above).

As of bash-4.4 (September 2016) all the loadables are now built and installed by default on platforms that support it, though they are built as separate shared-object files, and without a .so suffix. Unless your distro/OS has done something creative (sadly RHEL/CentOS 8 build bash-4.4 with loadable extensions deliberately removed), you should be able to do instead:

[ -z "$BASH_LOADABLES_PATH" ] &&
  BASH_LOADABLES_PATH=$(pkg-config bash --variable=loadablesdir 2>/dev/null)  
enable -f sleep sleep

(The man page implies BASH_LOADABLES_PATH is set automatically, I find this is not the case in the official distribution as of 4.4.12. If and when it is set correctly you need only enable -f filename commandname as required.)

If that's not suitable, the next easiest thing to do is build or obtain sleep from GNU coreutils, this supports the required feature. The POSIX sleep command is minimal, older Solaris versions implemented only that. Solaris 11 sleep does support fractional seconds.

As a last resort you could use perl (or any other scripting that you have to hand) with the caveat that initialising the interpreter may be comparable to the intended sleep time:

$ perl -e "select(undef,undef,undef,0.1);"
$ echo "after 100" | tclsh

Solution 2

The documentation for the sleep command from coreutils says:

Historical implementations of sleep have required that number be an integer, and only accepted a single argument without a suffix. However, GNU sleep accepts arbitrary floating point numbers. See Floating point.

Hence you can use sleep 0.1, sleep 1.0e-1 and similar arguments.

Solution 3

Sleep accepts decimal numbers so you can break it down this like:

1/2 of a second

 sleep 0.5

1/100 of a second

sleep 0.01

So for a millisecond you would want

sleep 0.001

Solution 4

Try this to determine accuracy:

    time sleep 0.5      # 500 milliseconds (1/2 of a second)
    time sleep 0.001    # 1 millisecond (1/1000 of a second)
    time sleep 1.0      # 1 second (1000 milliseconds)

Combination of mr.spuratic's solution and coles's solution.

Solution 5

You may simply use usleep. It takes microseconds (= 1e-6 seconds) as parameter, so to sleep 1 millisecond you would enter:

usleep 1000

View more solutions

Comments

[Tom O'Connor]

Can I ask why you want to sleep for 1ms?

[yael]

Yes of course , in my bash script I add "sleep 1" , in some lines , but script run very slowly , so after some conclusion I calculate that sleep 0.1 also bring good results and more faster About the delay , I need delay in order to solve the ssh problem in my bash script , I perform paralel ssh login to some machines by expect and without delay its will not work , As you know from my question the delay should fit both Linux and Solaris

[scai]

Whatever solution you choose, keep in mind that a shell script won't be very accurate in terms of timing.

[Tom O'Connor]

How about doing something that takes a very short time to execute, but does nothing.. like echo "" >/dev/null

[yael]

Good idea but how msec this command take? , I need 0.1 msec , not less then that -:)

[alanc]

Support for decimal arguments in Solaris sleep was added in Solaris 11. For older OS'es try installing GNU coreutils.

[Perette]

Beware! In macOS Sierra (at least the initial 10.12 release), ksh's built-in sleep does not work correctly for values ≤ 30. $ time sleep 5 real 0m0.00s user 0m0.00s sys 0m0.00s $ time sleep 30 real 0m0.00s user 0m0.00s sys 0m0.00s $ time sleep 31 real 0m31.01s user 0m0.00s sys 0m0.00s

[Alexander Mills]

these solutions seem overly complex, is that not a simpler way to do this? sleep -ms 50?

[yael]

see my remark about SOLARIS OS

[scai]

Did you mix up is and isn't?

[yael]

for example - I run on solaris 10 this: # sleep 0.1 sleep: bad character in argument , about linux sleep 0.1 works fine

[mr.spuratic]

Ah, since you're using expect you can probably just use "after N", where N is milliseconds, directly in your script.

[Mike Causer]

You can also drop the leading zero before the decimal point. eg. sleep .5

[kevinarpe]

Note: The built-in Bash command sleep is different from the external / separate binary sleep, which is usually installed in /bin/sleep or /usr/bin/sleep. By default, Bash will use the built-in, so use "$(which sleep)" to be very clear about using external binary.

[Ilan.K]

use usleep like @Luis Vazquez and @sebix write

[user]

You could at least change that bare usleep() call to if(argc == 1) { usleep(atoi(argv[1])); } to avoid indexing outside of the bounds of the array, which can lead to any number of unexpected behaviors.

[Luis Vazquez]

No, i mean usleep part of the initscripts package which is standard at least in all the Red Hat derived distributions; including at least RHEL, CentOS, Fedora, Mageia/Mandriva and SuSE. Here an example: `` ``

[Luis Vazquez]

Here is a sample ilustration running in CentOS 7: ``` $ which usleep /usr/bin/usleep $ rpm -qf /usr/bin/usleep initscripts-9.49.37-1.el7_3.1.x86_64 ``` To summarize: - sleep (from coreutils) works with seconds - usleep (from initscripts) works with micro-seconds

[stark]

Except for mathforum.org/library/drmath/view/52352.html

[Martin]

Talk about everyone else overcomplicating it...

[Alexander Mills]

@MikeCauser leading zeros much more readable and signal intent to the reader of the code later. also better when you actually do math.

[Déjà vu]

Also note that usleep unit is μs, so to wait 1 second, you need to provide a 1000000 argument.

[user]

@RingØ Right. Stupid mistake, good catch.

[Andrew Henle]

atoi() is a horrible choice to convert a string to an int. What does atoi( "STRING" ) return? atoi() has no way to return any error.

[roblogic]

Apple MacOS has BSD sleep, which also supports fractional seconds

[Ray Foss]

My Debian/Ubuntu based NodeJs image in CodeSandbox has sleep (GNU coreutils) 8.30 and supports this use of fractional seconds.