egrep - Extended Regular Expressions

Purpose of Document

This page defines how to specify patterns for some of my search engines.

Summary

An item is selected if there is a line in it that contains a substring that matches the pattern. The search is carried out by a PHP function and that uses the POSIX campatible syntax. This is very close to the traditional UNIX egrep form. expression(RE).

Example Patterns

• An item which has the string "Compiler" in it.

   Compiler

• Items with various spellings of "Dijkstra" with the j replaced by any character

   Di.kstra

• Items with various spellings of "Dijkstra" with the "ijk" replaced by any number of characters

   D.*stra

• An item with either "Compiler" or "compiler" in it.

   [cC]ompiler

• String like bananas, banananas, bananananas etc.

   bana(na)+s

• Items with the strings "regular" and "expression" on the same line withanything or nothing between them

   regular.*expression

• Items with either regular or expression (or both).

   regular|expression

• Items with either OO or "Object Oriented" on one line.

   OO|([oO]bject( |\-)[oO]riented)

• To search for characters other than letters or digits put a "\" in front of them.

   S\/SL

Formal Definition

1. Item::=@Line. Each Item is essentially a set of Lines -- because the order is not important to the search.

2. Line::=#char. A given line either matches or does not match a pattern... the set of matching Lines is written M: M:: pattern->@Line. The lines that match a given pattern

   An item is selected by a pattern, if any of its lines matches the pattern:

3. For Item I, pattern p, selected(I,p)::= for some L:I(L in M(p) ).

   Typically M(p) is any string that contains a string that matches P:pattern where pattern is defined by

4. pattern::= See http://csci.csusb.edu/dick/samples/regular_expressions.html

   Lexemes

5. char::=the set of ASCII characters.
6. empty::@#char= {""}.

   Glossary

7. egrep::UNIX_command=Extended Global Regular Expression Print.

8. RE::="Regular Expression(s)". -- an expression constructed out of sequences+selectios+iterations.

. . . . . . . . . ( end of section Lookup) <<Contents | End>>