How can I remove non-printable invisible characters from string?

Question

How can I remove non-printable invisible characters from string?

Ruby version: 2.4.1

2.4.1 :209 > product.name.gsub(/[^[:print:]]/,'.')
 => "Kanha‬" 
2.4.1 :210 > product.name.gsub(/[^[:print:]]/,'.').length
 => 6 

2.4.1 :212 > product.name.gsub(/[\u0080-\u00ff]/, '').length
 => 6 

2.4.1 :214 > product.name.chars.reject { |char| char.ascii_only? and (char.ord < 32 or char.ord == 127) }.join.length
 => 6 

2.4.1 :216 > product.name.gsub(/[^[:print:]]/i, '').length
 => 6 

The word "Kanha" has 5 letters. However there is a 6th character that is not printable. How can I remove it?

By googling and SOing I have already tried few approaches, but as you can see none of those are helpful.

It is causing problems when I try to integrate out data with other systems.

Answer 1

First, let's figure out what the offending character is:

str = "Kanha‬"
p str.codepoints
# => [75, 97, 110, 104, 97, 8236]

The first five codepoints are between 0 and 127, meaning they're ASCII characters. It's safe to assume they're the letters K-a-n-h-a, although this is easy to verify if you want:

p [75, 97, 110, 104, 97].map(&:ord)
# => ["K", "a", "n", "h", "a"]

That means the offending character is the last one, codepoint 8236. That's a decimal (base 10) number, though, and Unicode characters are usually listed by their hexadecimal (base 16) number. 8236 in hexadecimal is 202C (8236.to_s(16) # => "202c"), so we just have to google for U+202C.

Google very quickly tells us that the offending character is U+202C POP DIRECTIONAL FORMATTING and that it's a member of the "Other, Format" category of Unicode characters. Wikipedia says of this category:

Includes the soft hyphen, joining control characters (zwnj and zwj), control characters to support bi-directional text, and language tag characters

It also tells us that the "value" or code for the category is "Cf". If these sound like characters you want to remove from your string along with U+202C, you can use the \p{Cf} property in a Ruby regular expression. You can also use \P{Print} (note the capital P) as an equivalent to [^[:print]]:

str = "Kanha‬"
p str.length # => 6

p str.gsub(/\P{Print}|\p{Cf}/, '') # => "Kahna"
p str.gsub(/\P{Print}|\p{Cf}/, '').length # => 5

See it on repl.it: https://repl.it/@jrunning/DutifulRashTag