In regular expressions, in addition to ordinary symbols, the
following metasymbols can be used:
Beginning of line.
End of line.
Interpret next symbol literally.
Zero or more times.
One or more times.
Exactly n times.
Not less than n times.
From n to m times.
Any simbol from the set (a range is indicated by symbol -);
for example, [aeiou0-9] matches any symbol of
a, e, i, o, u,
and digit from 0 to 9; other operators and
metasymbols don't work in the brackets.
None of the set, for example, [aeiou0-9] is none
of the set a, e, i,
o, u, and none of digits from 0 to 9.
Any alpha-numeric symbol (including "_").
Any non-alphanumeric symbol.
Space symbol (space or tab).
Line delimiter (for multi-lines patterns).
Previous or next pattern, for example, fee|fie|foe
means "fee" or "fie" or "foe".
The round brackets group a subexpression, which can be used for