Pattern Matching - Characters

Literal Characters

• will match the exact character in the string
• includes:
  • digits (0-9)
  • Uppercase and lowercase letters (A-Z, a-z)
  • escaped characters

Escaped Characters

• there are few character the require escaping to use literally
• backlash () turns off the special meaning of a character
• Characters required to be preceded with a backslash()
  • ^$+?*()\

Literal Examples

'Hello!'
'Goodbye\.' # escape the dot
'End of the line\.\n' # escape the dot, white space new line
'\$100\.00' # escape the dollar sign
'24\+36=60' # escape the + sign
'\\t means tab'

Character Classes

• Contains a range or series of characters
• Correspond to matching a single character
• Surrounded by square brackets

Defining Character Classes

• within square brackets []:
  • we place one or more literal characters in it
  • we can also place a character range using a start character, a dash and an ending character by specifying a starting character, a dash and an ending character Caret (^) [invert he character class by placing] at the beginning of indicates inverse matching

Character Classes Examples

[ABCD] # match only A, B, C or D
[aeiou] # match only a,e,i,o,u
[B-E] # match only B, C, D or E
[^B-E] # match anything but B, C, D or E
[a-z0-5] # match letter from a-z(lowercase) or number 0-5.
[^A-z] # match only non alphabet characters

Character Class Matching

screenshots

Character Classes Shorthand

• Shorthand to frequently used character classes:
  • Alphanumeric, numeric and whitespace ranges
  • Inverse of the above ranges
  • The dot (.) character matches any character

Shorthand Character Classes

Shorthand	Equivalent	Description
.	.	match any single character except newline
\w	[A-z0-9_]	alphanumeric and _
\W	[^A-z0-9_]	non - alphanumerics
\d	[0-9]	digits
\D	[^0-9]	non digits
\s	[ \b\f\n\r\t\v]	whitespace
\S	[^ \b\f\n\r\t\v]	non whitespace

Shorthand Examples

Pattern	Description
...	match any three characters
\d\d	match any two digits
\w\w\w	match any three alphanumeric characters
\S	match a single - non whitespace character
[A-z]\W	match one alphabet followed by a non white space
\d\d\D\D	match two digits followed by two non-digits
\s\w\s	match one alphanumeric characters surrounded by whitespace

Shorthand Matching Examples

• three consecutive digits match

Pattern	String
[0-9][0-9][0-9]	510
\d\d\d	510
\d\d\d	94704
\d\d\d	x300
\d\d\d	42 [no match]