Possible positive lookbehind: 
$_ = "fox comes and fox goes into forest";
#s/(.+)(fox)/$1 the $2/;
#s/(?<=and)(?:\s+fox)/ the/;
s/(?<=fox)(.+?)(fox)/$1 the $2/;

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In reply to Re: regexp find last word by sh1tn
in thread regexp find last word by Murcia

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