Answer:
[0-9]* matches strings of any length (including zero), composed entirely of digits.
[^0-9]* matches strings of any length (including zero), composed entirely of NON-digits.
[0-9]* matches strings of any length (including zero), composed entirely of digits.
[^0-9]* matches strings of any length (including zero), composed entirely of NON-digits.
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Regular Expression (Delimit with quotes) |
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String (Delimit with quotes) |
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Some character classes are so useful that short-cuts have been defined for them.
Digits: \d means the same as
[0-9].
Whitespace: \s matches
space, tab, newline, vertical tab, formfeed, and carriage return.
This is useful because it matches more than just space, and prevents the problems of spaces in an RE.
Non-Whitespace: \S matches
everything but whitespace.
To match more than one of these, use *,
+, and
{n,m}. For example
\d*
matches digit strings of any length.
Notice that the * applies to the entire \d, not just the d character.
The table shows several additional shortcuts.
| Short Cut | Equivalent | Description |
|---|---|---|
\d | [0-9] | A digit |
\D | [^0-9] | A non-digit |
\s | [ \t\n\x0B\f\r] | A whitespace character |
\S | [^\s] | A non-whitespace character |
\w | [a-zA-Z_0-9] | A word character |
\W | [^\w] | A non-word character |
Write a regular expression that matches strings consisting of one or more digits, but not starting with digit 0, surrounded by any amount of whitespace on either or both sides. For example:
" 123" "1023 " "4" " 7" "2210"
But not:
"0" "0123 " " 0 "