There's actually no error - all you're seeing is a couple of warnings because you have warnings enabled.

If you really want to exit if the substr is outside of the string, then I can't think of any option significantly different to the one you've suggested.

If you're more interested in just not seeing the warnings you could disable warnings altogether or change the code to: 
use warnings;
no warnings ('uninitialized', 'substr');
my $str="name";
my $index=12;
my $s=substr($str,$index,1);
print $s;

[download]

Cheers,
Rob

In reply to Re: substr outside of string by syphilis
in thread substr outside of string by kulls

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