Regular Expression Examples
[Overview]

Regular Expression Examples

Regular Expression Metacharacters

Meatcharactes:

{}[]()^$.|*+? : Character with a special meaning. If you want to look for these characters 
                in your text, preceed them with a backslash \ (i.e. \$)

^   : Matches the starting position within the string. In line-based tools, it matches the 
      starting position of any line.
.   : Matches any single character (many applications exclude newlines, and exactly which 
      characters are considered newlines is flavor-, character-encoding-, and platform-specific, 
      but it is safe to assume that the line feed character is included). Within POSIX bracket 
      expressions, the dot character matches a literal dot. For example, a.c matches "abc", etc., 
      but [a.c] matches only "a", ".", or "c".
[ ] : A bracket expression. Matches a single character that is contained within the brackets. 
      For example, [abc] matches "a", "b", or "c". [a-z] specifies a range which matches any 
      lowercase letter from "a" to "z". These forms can be mixed: [abcx-z] matches "a", "b", "c", 
      "x", "y", or "z", as does [a-cx-z].

      The - character is treated as a literal character if it is the last or the first (after the ^, 
      if present) character within the brackets: [abc-], [-abc]. Note that backslash escapes are not 
      allowed. The ] character can be included in a bracket expression if it is the first (after the ^) 
      character: []abc].
[^ ]: Matches a single character that is not contained within the brackets. For example, [^abc] 
      matches any character other than "a", "b", or "c". [^a-z] matches any single character that 
      is not a lowercase letter from "a" to "z". Likewise, literal characters and ranges can be mixed.
$ :   Matches the ending position of the string or the position just before a string-ending newline. 
      In line-based tools, it matches the ending position of any line.
( ) : Defines a marked subexpression. The string matched within the parentheses can be recalled 
      later (see the next entry, \n). A marked subexpression is also called a block or capturing group. BRE mode requires \( \).
\n :  Matches what the nth marked subexpression matched, where n is a digit from 1 to 9. This 
      construct is vaguely defined in the POSIX.2 standard. Some tools allow referencing more than 
      nine capturing groups. Also known as a backreference.

Quantification:

?         : The question mark indicates zero or one occurrences of the preceding element. For example, 
            colou?r matches both "color" and "colour". 
*         : The asterisk indicates zero or more occurrences of the preceding element. For example, ab*c 
            matches "ac", "abc", "abbc", "abbbc", and so on.
+         : The plus sign indicates one or more occurrences of the preceding element. For example, ab+c 
            matches "abc", "abbc", "abbbc", and so on, but not "ac".
{n}       : The preceding item is matched exactly n times.
{min,}    : The preceding item is matched min or more times.
{,max}    : The preceding item is matched up to max times.
{min,max} : The preceding item is matched at least min times, but not more than max times. 

Character classes;

[:digit:] : 0-9
[:alnum:] : A-Z,a-z,0-9
[:alpha:] : A-Z,a-z
[:blank:] :<space>, <tab>
[:punct:] : [][!"#$%&'()*+,./:;<=>?@\^_`{|}~-]
[:space:] : whitespace characters [ \t\r\n\v\f]
[:upper:] : A-Z
[:lower:] : a-Z
[:print:] : visible characters and <space>
\b        : word boundary  (zero width word boundary between a alphanumeric character and 
            a non alphanumeric character)
\w        : alphanumeric including _
\s        : whitepace character
\d        : 0-9
\W        : inverse of \w
\S        : inverse of \s
\D        : inverse of \d
for further information see the wiki page Regular expression

examples assembled by andreas schmidt for the DBKDA 2021 conference