$var =~ s[\bt(?!est).*?t\b\s*][]g;

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Update: sauoq's right. I omitted a \b. 

perl> $var = "thought testament test tot 1 2 3 tesset";
perl> $var =~ s[\bt(?!est\b).*?t\b\s*][]g; print $var;
test 1 2 3

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Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail
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In reply to Re: A regex that does this, but not that? by BrowserUk
in thread A regex that does this, but not that? by bradcathey

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