Metacharacter Represents
^ Matches at the beginning of a line
$ Matches at the end of a line
a.c Matches an 'a', any single character, and a 'c'
[abc] Matches an 'a' or 'b' or 'c'
[^abc] Matches a character that is not an 'a' or 'b' or 'c'
[0-9] Matches one digit between '0' and '9'
ab*c Matches an 'a', followed by zero or more 'b's and a 'c'
ab+c Matches an 'a', followed by one or more 'b's and a 'c'
ab?c Matches an 'a', followed by zero or one 'b' and a 'c'
(ab)+c Matches one or more occurrences of 'ab' followed by a 'c'
(ab)(c) Captures 'ab' and assigns it to $1, captures 'c' and assigns it to $2.