Filter valid hexadecimal color codes

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# 1  
Old 04-20-2020
Filter valid hexadecimal color codes

So I have a text file containing valid and invalid hexadecimal color codes. Would I need to build a custom c program to filter the valid color codes or would a standard unix command achieve this?
# 2  
Old 04-20-2020
well... first, you'd need to define what makes the code "invalid".
Them look at your "text file" and try to determine the logical pattern how to make the "call".
# 3  
Old 04-20-2020
So I think I found out a good way of doing it by using grep and regular expression to filter out the non-valid codes but it doesn't seem to work and I don't know why

grep "^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})" colours.txt

# 4  
Old 04-20-2020
I don't know either...
Most likely because you're using Extended RegEx without telling grep to do so (-E)
could you provide a sample file and a desired output (as always)?
# 5  
Old 04-20-2020
I tried grep -E and it didn't work. I've attached the text file that I am using and I basically want to return valid codes that have a hash symbol and have 6 or 8 characters ranging from A-Z, a-z or 0-9.

grep -E "^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{8})" colours.txt

# 6  
Old 04-20-2020
how about to start with - you can enhance it to match ONLY 6 or 8 chars (not 6 though 8 including 7) - left as an exercise:
grep -iE '^#[a-f0-9]{6,8}$' colours.txt

This User Gave Thanks to vgersh99 For This Post:
# 7  
Old 04-20-2020
How about - after removing the DOS line terminators (<CR> = ^M = 0x0D = \r) that sabotage any regex -

grep -E "#[[:xdigit:]]{6}([[:xdigit:]]{2})?$" colours.txt

This User Gave Thanks to RudiC For This Post:
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