Character classes in linux shell

Here is the list of character classes in Linux. They are used in pattern matching.
  • [:alpha:] matches letters only.
  • [:digit:] matches numbers only.
  • [:alnum:] matches letters and numbers only.
  • [:xdigit:] matches hexadecimal numbers.
  • [:lower:] matches a-z.
  • [:upper:] matches A-Z.
  • [:blank:] matches a space or a tab.
  • [:space:] matches white space and horizontal tab.
  • [:cntrl:] matches control characters.
  • [:print:] Printable characters in the range of ASCII 32 – 126.
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