How to make the Perl script work only in one copy


It is sometimes necessary to write a Perl script that runs only if this same script is not working. I.e., to guarantee that at one point of time only one instance of this script.

For example, this problem may occur if the script is run for the crown every minute and sometimes it can run more than a minute.

Here we are talking about the case when the script works on one server and you want to ensure execution is not more than one instance of the script on the same machine.

The decision

The easiest way to solve this problem is to use the Perl library Sys::RunAlone.

The library comes with Perl, it needs to be installed additionally.

To make a script that only works in one instance, you need to add in the existing script use Sys::RunAlone; and __END__.

Here is an example of a script that works only in one instance:


use Sys::RunAlone;

print "working\n";

sleep 10;


If you run this script, it displays the text working and 10 seconds to hang and wait, and then exits.

If you open another console and while the script is running to try to run it one more time this run will fail, and no code from the script will not be executed:

$ perl
A copy of '' is already running

Unit __END__ in the script is mandatory. Library Sys::RunAlone uses this the unit in order to take Locke. And if this block is not, and the library Sys::RunAloneconnected the script will not work, the screen will display error Add __END__ to end of script '' to be able use the features of Sys::RunALone.

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