If you want to delete a portion of a string using the four-arg version of substr, this works, but issues a warning: 

$s = 'fred';;
substr $s, 1,2,undef;;
Use of uninitialized value in substr at (eval 7) line 1, <STDIN> line 
+2.

print $s;;
fd

[download]

The warning is easily avoided by using '' instead of undef, but that seems a little unperlish to me?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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In the absence of evidence, opinion is indistinguishable from prejudice.
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In reply to Use of uninitialized value in substr by BrowserUk

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