Regular expressions can take quite an effort to get right, but at the same time can be very powerful. VOPP supports most of the standard POSIX regex. A summary of regular expression terms and their meanings is included below. For a more detailed discussion please read
http://www.delorie.com/gnu/docs/regex/regex_toc.html
Match any character
n . (single)
e.g. d.g matches a string starting with d, ending with g, with any one character in between: dog will match, dg will not
Repetition operators
n * (zero or more)
e.g. do*g matches a string made up of zero or more "o" characters: dooog, doog, dog, dg all match
n + (one or more)
e.g. do+g matches a string made up of one or more "o" characters: dooog, doog, dog match, but dg doesn't
n ? (zero or one)
e.g. do?g matches zero or more "o" characters: dooog, doog don't match, but dog, dg do match
n {} (interval expression)
n {n} matches n occurrences of the preceding expression
n {n,} matches n or more occurrences of the preceding expression
n {n,m} matches at least n, but not more than m occurrences of the preceding expression
Anchoring
n ^ match beginning of line
Escape
n \ Escape character - use next character as is
Alternation
n | (or)
e.g. dog|cat will match dog or cat
Lists
n [] (set of one or more items)
n [ab] matches any a or b
n [^ab] matches any character except a or b
n [a-z] matches any alphabetic character
n [a-z0-9] matches any alphabetic or digit character
Grouping
n () (parentheses signify a regular expression group)
Replace
n & insert the original string found
n #0, #1, etc Each parentheses set, (), in the search expression denotes a group. Group numbering starts at zero. Specifying #n in the replace will insert the string that was matched by group n.
NOTE 1: spaces within regular expression _are_ significant
NOTE 2: see dimension example for important concept regarding matching
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Regular Expressions
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