match any number of characters regex code example

Example 1: regex for counting characters

( *?[0-9a-zA-Z] *?){10,}

Example 2: 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.txt