Mask certain file paths in binary files - binary

Question

I have a binary file containing some file paths. If the path starts with a certain string, the rest of the file path [\x20-\x7f]+ should be masked, leaving the general structure and size of the file intact!
So with a list of paths to search for is this:
/usr/local/bin/
/home/joe/
Then an occurrence like this in the binary data:
^#^#^#^#/home/joe/documents/hello.docx^#^#^#^#
Should be changed to this:
^#^#^#^#/home/joe/********************^#^#^#^#
What is the best way to do this? Do sed, perl or awk have a way? Or do I have to write a C or PHP program where I find the string and write strlen() number of mask characters in its place?

Answer 1

perl is a good choice for working on binary data. For sed and awk, only the GNU implementations can generally cope with binary data, the other ones would choke on the NUL byte or on long sequences between two newline characters, or on non-terminated lines.
perl -pi.back -e 's{(/usr/local/bin|/home/joe)/\K[\x20-\x7f]+}{
$& =~ s/./*/rg}ge' binary-file
You'd need not too old a version of perl for the /r flag (returns the result of the substitution instead of applying it on the variable) and \K (reset the start of the matched string).
By default, perl -p works on one line at a time, since the newline character is not part of [\x20-\x7f], that's fine.

Answer 2

Here is some perl code that works, though I'm sure it can be optimised. It is a filter, so it reads all of stdin into $data, then for each string in the array #dirs it does a substitute for the pattern. The replacement however is not a fixed string but a function call replace($dir,$1) which is evaluated because of the e modifier to the substitute command.
#!/usr/bin/perl
use strict;
sub replace{
my ($dir,$rest) = #_;
$rest =~ s/./*/g;
return $dir.$rest;
}
my #dirs = ('/usr/local/bin/','/home/joe/');
my $data = join("",<STDIN>);
foreach my $dir (#dirs){
$data =~ s|$dir([\x20-\x7f]+)|replace($dir,$1)|ge;
}
print $data;
The function is given 2 arguments, the directory and the captured part of the pattern. It returns these concatenated after replacing each character in the captured string.