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Oracle PL/SQL Tutorial » Regular Expressions Functions » Meta characters 
18. 6. 1. Meta characters

In Regrlar Expresions, there are three special characters that are used in matching patterns:

  1. "^" - a caret is called an "anchoring operator," and matches the beginning of a string. The caret may also mean "not," which is at best confusing.
  2. "$" - a dollar sign is another anchoring operator and matches only the end of a string.
  3. "." - the period matches anything and is called the "match any character" operator. Many would call this a "wildcard" match character.
  4. + matches one or more repetitions of the preceding RE
  5. * matches zero or more repetitions of the preceding RE
  6. ? matches zero or one repetition of the preceding RE
18. 6. Meta characters
18. 6. 1. Meta characters
18. 6. 2. The period may be substituted for any letter and still maintain a match
18. 6. 3. Use the caret-anchor to insist the matching start at the beginning of the string
18. 6. 4. Asking for a match for a capital 'F' followed by any character
18. 6. 5. The search string cannot be anchored at the beginning and then searched from some other position
18. 6. 6. Negating Carets
18. 6. 7. A '^' followed by something else like an 'l' (a lowercase 'L')
18. 6. 8. Match a string where 'i' is followed by any one character and followed by another 'i'
18. 6. 9. Regexp_Substr
18. 6. 10. '*' matches zero or more repetitions
18. 6. 11. '+' matches one or more repetitions
18. 6. 12. '?' matches exactly zero or one repetition
18. 6. 13. Asking to match an 'a' and zero or more 'b's:
18. 6. 14. A series of 'b's immediately following the 'a'
18. 6. 15. Matching at least one 'b'
18. 6. 16. Want an 'e' followed by any number of other characters and then another 'e'
18. 6. 17. REGEXP_SUBSTR(value,'e.*e')
18. 6. 18. Non-greedy '?'
18. 6. 19. Empty Strings and the ? Repetition Character
18. 6. 20. The '?' says to match zero or one time
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