my $var = "thought test tot 1 2 3 tesset";

##</code><code>##

test 1 2 3

##</code><code>##

$var =~ s/((t.*?t)([\w ]*test[\w ]*)(t.*?t))/$3/g;

##</code><code>##

test tot 1 2 3

##</code><code>##

$var =~ s/(t.*?t) but not (test)//g;