Using Tr To Remove Certain Characters And Keep Oth

tr -dc ‘[:alnum:]\n\r’ | tr ‘[:upper:]’ ‘[:lower:]’

• tr deletes special characters.
• d is delete.
• c is complement (invert the character set).
• dc is therefore, delete all characters, except those specified.
• Can preserve certain characters, such as \n and \r above.
• The second line translates uppercase characters to lowercase.