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In regular expressions, what is the difference between ^[a-zA-Z]+$ and ^[a-zA-Z]*$. Also would I be able to not include it at all, either with ^[a-zA-Z]$ or ^[a-zA-Z].
I looked online and it says that + matches the preceding character one or more times and * matches the preceding character zero or one times, but I have no idea what this means in this context, or at all.
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[] denotes a character class. () denotes a capturing group. [a-z0-9] -- One character that is in the range of a-z OR 0-9. (a-z0-9) -- Explicit capture of a-z0-9 .
*? is non-greedy. * will match nothing, but then will try to match extra characters until it matches 1 , eventually matching 101 . All quantifiers have a non-greedy mode: . *? , .
Regular expressions are useful in any scenario that benefits from full or partial pattern matches on strings. These are some common use cases: verify the structure of strings. extract substrings form structured strings.
+ means 1 or more
* means 0 or more
So an empty string is found by ^[a-zA-Z]*$, but not by ^[a-zA-Z]+$
^[a-zA-Z]$ means EXACTLY one letter in the ranges a-z and A-Z.
a+ is a, aa, aaa, ..., aaa...aaa, etc
a* is an empty string, a, aa, aaa, ..., aaa...aaa, etc
^a$ is only a
EDIT: you can also use ^a?$ to find 0 or 1 occurence of a, so either an empty string or a
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