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The above regular expression (in Java) matches a string of alpha numeric characters of length between 5 and 10.
How can I modify the above regular expression to match with the above requirements as well as matching with an empty string?
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The bracketed characters [a-zA-Z0-9] indicate that the characters being matched are all letters (regardless of case) and numbers. The * (asterisk) following the brackets indicates that the bracketed characters occur 0 or more times.
$ means "Match the end of the string" (the position after the last character in the string). Both are called anchors and ensure that the entire string is matched instead of just a substring.
Most characters, including all letters ( a-z and A-Z ) and digits ( 0-9 ), match itself. For example, the regex x matches substring "x" ; z matches "z" ; and 9 matches "9" . Non-alphanumeric characters without special meaning in regex also matches itself. For example, = matches "=" ; @ matches "@" .
Using character sets For example, the regular expression "[ A-Za-z] " specifies to match any single uppercase or lowercase letter. In the character set, a hyphen indicates a range of characters, for example [A-Z] will match any one capital letter.
Make it optional (match exactly one or zero times)
^([a-zA-Z0-9]{5,10})?$
^(?:[a-zA-Z0-9]{5,10}|)$
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