If one of the tags overlaps the record boundary with the fixed length read, you can do the substitition on two blocks at a time. Pseudocode: 
use constant BLOCKLENGTH => 32768; # > length of any tag
$\ = \BLOCKLENGTH;
my $buffer = '';
while (!eof()) {
   $buffer .= <>;
   s/tag1/\n/g;
   s/tag2/\t/g;
   # leave BLOCKLENGTH chars in $buffer,
   # print however much comes before that
   print substr($buffer, 0, -BLOCKLENGTH, '');
};
# print whatever's left
print $buffer;

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Alternatively, just do a while(<>) loop with the substitution and print inside, but run it twice with two different record lengths such that no multiples (less than the file size) of the two come within a distance of each other less than the length of the longest tag. Don't know quite how to go about calculating such numbers, though. Any number theoreticians here?

In reply to Re: Re: search/replace very large file w/o linebreaks by ysth
in thread search/replace very large file w/o linebreaks by Anonymous Monk

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