regex pater for only 4 or 6 digits
^([0-9]{4}|[0-9]{6})$regex match any number of digits
For matching an integer number of one single char/digit, specify:
[0-9]
But for matching any number of more than one char/digit; add "+":
[0-9]+
Example for matching hour with minutes of HH:MM format in a file:
grep "[0-9]+:[0-9]+" file.txtCopyright © 2021 Codeinu
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