Another way to avoid the warning is to locally disable warnings within a block. Maybe more Perlish: 
use strict;
use warnings;

my $s = 'fred';;
{
    no warnings;
    substr $s, 1,2,undef;;
}
print $s;;

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Update: BrowserUk is correct ... I am not licensed to assess if one solution is more Perlish than another. The judge will instruct the jury to ignore that remark :)

In reply to Re: Use of uninitialized value in substr by toolic
in thread Use of uninitialized value in substr by BrowserUk

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