Literal Characters ...


• \0 zero   NULL
• \t lowercase t   TAB
• \n lowercase n   New Line
• \v lowercase v   Vertical tab
• \f lowercase f   Form Feed
• \r lowercase r   Carriage Return
• \xnn lowercase x   Hexadecimal character represented by nn
• \d lowercase d   matches any digit 0-9
• \D uppercase D   matches what is not a digit
• \w lowercase w   matches any alphanumeric, a-zA-Z0-9_
• \W uppercase W   matches what is not alphanumeric
• \c lowercase c   matches any alphabetic, a-zA-Z
• \C uppercase C   matches what is not alphabetic, a-zA-Z
• \s lowercase s   matches any whitespace character
• \S uppercase S   matches any non-whitespace character

Punctuation Characters ...


• ^ carat   match the beginning of a string or line
• $ dollar sign   match the end of a string or line
• . stop   wildcard - matches any character
• * asterisk   zero or more matches
• + plus   one or more matches
• ? question mark   the match is optional, may or may not match
• | vertical bar   alternative (or)
• \ back slash   escape character, the following character has a specific meaning
• ( ) round brackets   subexpression
• { } braces   number of occurrences to match
• [ ] square brackets   sequence or range of characters to match

Examples ...

text='alpha'
expression='qwe'
     will not find a match,
     and so return a -1.

text='alpha'
expression='h'
     will find a match starting in position 4,
     and so return a 4.

text='alpha'
expression='\w'
     will find a match starting in position 1,
     and so return a 1.

text='alpha'
expression='\W'
     will not find a match,
     and so return a -1.

text='alp25a'
expression='\d'
     will find a match starting in position 4,
     and so return a 4.

text='myname@emailaddress.zx'
expression='\w+@\w+\.\w{2,3}$'
     will find a match starting in position 1,
     and so return a 1.

text='myname@emailaddress.zxy'
expression='\w+@\w+\.\w{2,3}$'
     will find a match starting in position 1
     and so return a 1.

text='myname@emailaddress.zxywv'
expression='\w+@\w+\.\w{2,3}$'
     will not find a match,
     and so return a -1.

text='myname@emailaddress.zx'
expression='\w+@\w+\.\w{2,3}'
     will find a match starting in position 1,
     and so return a 1.

text='myname@emailaddress.zxy'
expression='\w+@\w+\.\w{2,3}'
     will find a match starting in position 1,
     and so return a 1.

text='myname@emailaddress.zxywv'
expression='\w+@\w+\.\w{2,3}'
     will find a match starting in position 1,
     and so return a 1.

text='alph123'
expression='^\w+\d'
     will find a match starting in position 1,
     and so return a 1.

text='alph123'
expression='^\w\d'
     will not find a match,
     and so return a -1.