Question

I want to get rid of all invalid characters; example hexadecimal value 0x1A from an XML file using sed.
What is the regex and the command line?
EDIT
Added Perl tag hoping to get more responses. I prefer a one-liner solution.
EDIT
These are the valid XML characters

x9 | xA | xD | [x20-xD7FF] | [xE000-xFFFD] | [x10000-x10FFFF]

Answer 1

Assuming UTF-8 XML documents:

perl -CSDA -pe'
   s/[^\x9\xA\xD\x20-\x{D7FF}\x{E000}-\x{FFFD}\x{10000}-\x{10FFFF}]+//g;
' file.xml > file_fixed.xml

If you want to encode the bad bytes instead,

perl -CSDA -pe'
   s/([^\x9\xA\xD\x20-\x{D7FF}\x{E000}-\x{FFFD}\x{10000}-\x{10FFFF}])/
      "&#".ord($1).";"
   /xeg;
' file.xml > file_fixed.xml

You can call it a few different ways:

perl -CSDA     -pe'...' file.xml > file_fixed.xml
perl -CSDA -i~ -pe'...' file.xml     # Inplace with backup
perl -CSDA -i  -pe'...' file.xml     # Inplace without backup