That works if the replacement is character for character. You may be surprised by the results if the replacements are shorter than the original value.

open (A, '+<', "somefile.html") or die $!;
s/a/b/g for my @records = <A>;
seek(A, 0, 0);
###
truncate (A, 0) or die "can not truncate file to zero length\n";
###
print A @records;
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