Week 15 - Pattern Matching

Pattern Matching

Regular Expressions

Keyword search:

will only match the given value not any other (e.g. matt but not mat or mathew)

Metacharacters:

. = any one character, except new line
[a-z] = Any one of the enclosed characters
* = Zero or more of proceeding characters
? = Zero or one of the preceding character
+ = one or more of the preceding character
^ = Beginning of line
$ = End of line
\char = Escape meaning of char following it
[^] = One character not in the set

\d = Digit (0-9)
\D = Not a Digit (0-9)
\w = Word Character (a-z,A-Z,0-9,_)
\W = Not a Word Character
\s = Whitespace (Space, Tab, New Line)
\S = Not Whitespace
\b = Word Boundary
\B = Not a Word Boundary

Shorthand Classes:

[:alnum:] = Any Alphanumeric character
[:alpha:] = Any Alphabetic character
[:lower:] = Any Lowercase Character
[:upper:] = Any Uppercase Character
[:digit:] = Any Digits
[:space:] = Any Spaces

Examples:

[A-H] = [ABCDEFGH]
[A-Z] = Any Uppercase Alphabetic
[0-9] = Any Digit
[[a] = [ or a
[0-9\-] = Any digit or hyphen
[^AB] = Any Character except A or B
[A-Za-z] = Any Alphabetic
[^0-9] = Any Character except a digit
[]a] = ] or a
[^\^] = Anything except ^

Operators:

Sequence = None
Alternation = |
Repetition = \{m,n\}
Group = (...)
Save = \(...\)

Sequence Examples:

dog = matches the pattern "dog"
a..b = matches "a",any two characters, and "b"
[2-4][0-9] = Matches a number between 20 and 49
[0-9][0-9] = Matches any two digits
^$ = Matches a blank line
^.$ = Matches a one-character line
[0-9]-[0-9] = Matches two digites seperated by a "-"

Alternation Examples:

UNIX|unix = Matches "UNIX" or "unix"
Ms|Miss|Mrs = Matches "Ms" or "Miss" or "Mrs"

Repetition Examples:

Formats:

{m} = Matches previous atom exactly m times
{m, } = Matches previous atom m times or more
{ ,n} = Matches previous atom n times or less
{m,n} = Matches previous atom m times to n times

Examples:

CA{5} = Matches "CAAAAA"
CA{3,} = Matches "CAAA", "CAAAA", "CAAAAA", ...
CA{,2} = Matches "C", "CA", or "CAA"
A{3,5} = Matches "AAA","AAAA", or "AAAAA"
BA{3,6} = Matches "BAAA","BAAAA","BAAAAA", or "BAAAAAA"

Short Form Repetition Operators:

Formats:

* = Special case: Matches previous atom zero or more times
+ = Special case: Matches previous atome one or more times
? = Special case: Matches previous atom 0 or one time only

Examples:

BA* = Matches "B", "BA", "BAA", "BAAA", "BAAAA", ...
B.* = Matches "B","BA" ... "BZ","BAA" ... "BZZ","BAAA" ... "BZZZ", ...
.* = Zero or more characters
.+ = One or more characters
[0-9]? = Zero or one digit

Group Operator Examples:

A(BC){3} = Matches "ABCBCBC"
(F(BC){2}G){2} = Matches "FBCBCGFBCBCG"