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I am new to regex expressions in java. How do I check if the file name has the following format update_9_0_27 ?
Is it something like [0-9][\\_][0-9][\\_][0-100] ?
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The _ (underscore) character in the regular expression means that the zone name must have an underscore immediately following the alphanumeric string matched by the preceding brackets. The . (period) matches any character (a wildcard).
Special Regex Characters: These characters have special meaning in regex (to be discussed below): . , + , * , ? , ^ , $ , ( , ) , [ , ] , { , } , | , \ . Escape Sequences (\char): To match a character having special meaning in regex, you need to use a escape sequence prefix with a backslash ( \ ).
Variant 1: String matches() This method tells whether or not this string matches the given regular expression. An invocation of this method of the form str. matches(regex) yields exactly the same result as the expression Pattern. matches(regex, str).
Theoretically, an empty string also only consists of underscores; if that's undesirable you would need to also check whether strlen($str) is non-zero.
The following should work:
^[a-zA-Z]+_\d_\d_\d{1,2}$
The ^ and $ are beginning of string anchors so that you won't match only part of a string. Each \d will match a single digit, and the {1,2} after the final \d means "match between one and two digits (inclusive)".
If the update portion of the file name is always constant, then you should use the following:
^update_\d_\d_\d{1,2}$
Note that when creating this regex in a Java string you will need to escape each backslash, so the string will look something like "^update_\\d_\\d_\\d{1,2}$".
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