binmode STDIN;
binmode STDOUT;

# Could read in the entire file,
# but read in chunks ending with
# 00h to save memory.
$/ = "\x00"; 

while (<>) {
    s/(\x31\x33\x39\x37.*?\x00)/"\x00" x length($1)/e;

    # Or the following if you don't want
    # to replace the start and the end:
    #s/(\x31\x33\x39\x37)(.*?)(\x00)/
    #   $1 . ("\x00" x length($2)) . $3
    #/e;

    print;
}

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In reply to Re: Searching a file for an undetermined hexadecimal string by ikegami
in thread Searching a file for an undetermined hexadecimal string by Anonymous Monk

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