CodeBlocksPortable/WATCOM/eddat/regexp.hlp

Search And Replace Summary
==========================

Search Strings
--------------
regular-exp : {branch}|{branch}|...
branch :      {piece}{piece}...
piece :       {atom{* or + or ?}}{atom{* or + or ?}}...
	      * - match 0 or more of the atom
	      + - match 1 or more of the atom
	      ? - match a match of the atom, or the null string
atom :        (regexp) or range or ~ or @ or ^ or $ or \char or char
range :       [ {^} char and/or charlo-charhi ]  '^' causes negation of range
. :           match any character
^ :           match start of line
$ :           match end of line
@ :           what follows is to be searched with case sensitivity
~ :           what follows is to be searched without case sensitivity
! :           if it occurs as the FIRST CHARACTER in a regular expression,
	      it causes the ignoring of the NoMagic variable; that is,
	      all magic characters are treated as magical.  ! is treated
	      as a regular character if it occurs anywhere but at
	      the very start.
char :        any character
\char :       forces \char to be accepted as char (no special meaning)
	      execept for 
	      \t - match a tab (if RealTabs is set)

Replace Strings
---------------
& -     Each instance of `&' in the replacement string is replaced by the 
	entire string of matched characters
\\ -    Used to enter a '\' in the replacement string
\n -    Replaced with a new line
\t -	Replaced with a tab (if RealTabs is set)
\<n> -  Each instance of <n>, where n is a digit, is replaced by the
	n'th substring in the previous regular expression
\u -    Next item in replacement string is changed to upper case
\l -    Next item in replacement string is changed to lower case
\U -    All items following '\U' in the replacement string are changed to 
	upper case, until a '\E' or '\e' is encountered
\L -    All items following '\U' in the replacement string are changed to 
	lower case, until a '\E' or '\e' is encountered
\e,\E - Terminate \U or \L
\|<n> - substitutes spaces up to column <n>, so that the item that follows
	occurs at column <n>
\#    - substitutes current line number


Regular Expression Search Strings
=================================
A regular expression is zero or more branches, separated by `|'.
It matches anything that matches one of the branches.

A branch is zero or more pieces, concatenated.
It matches a match for the first, followed by a match for the second, etc.

A piece is an atom possibly followed by `*', `+', or `?'.
An atom followed by `*' matches a sequence of 0 or more matches of the atom.
An atom followed by `+' matches a sequence of 1 or more matches of the atom.
An atom followed by `?' matches a match of the atom, or the null string.

An atom is a regular expression in parentheses (matching a match for the
regular expression), a range (see below), 
`.' (matching any single character), `^' (matching the null string at the
beginning of the input string), `$' (matching the null string at the
end of the input string), a `\' followed by a single character (matching
that character), '~' (causing next stuff to be case sensitive), '@' 
(causing next stuff to be case insensitive), or a single character 
with no other significance (matching that character).

A range is a sequence of characters enclosed in `[]'.
It normally matches any single character from the sequence.
If the sequence begins with `^',
it matches any single character not from the rest of the sequence.
If two characters in the sequence are separated by `-', this is shorthand
for the full list of ASCII characters between them
(e.g. `[0-9]' matches any decimal digit).
To include a literal `]' in the sequence, make it the first character
(following a possible `^').
To include a literal `-', make it the first or last character.

If a regular expression could match two different parts of the line,
it will match the one which begins earliest.
If both begin in the same place but match different lengths, or match
the same length in different ways, life gets messier, as follows.

In general, the possibilities in a list of branches are considered in
left-to-right order, the possibilities for `*', `+', and `?' are
considered longest-first, nested constructs are considered from the
outermost in, and concatenated constructs are considered leftmost-first.
The match that will be chosen is the one that uses the earliest
possibility in the first choice that has to be made.
If there is more than one choice, the next will be made in the same manner
(earliest possibility) subject to the decision on the first choice.
And so forth.

For example, `(ab|a)b*c' could match `abc' in one of two ways.
The first choice is between `ab' and `a'; since `ab' is earlier, and does
lead to a successful overall match, it is chosen.
Since the `b' is already spoken for,
the `b*' must match its last possibility _the empty string_ since
it must respect the earlier choice.

In the particular case where no `|'s are present and there is only one
`*', `+', or `?', the net effect is that the longest possible
match will be chosen.
So `ab*', presented with `xabbbby', will match `abbbb'.
Note that if `ab*' is tried against `xabyabbbz', it
will match `ab' just after `x', due to the begins-earliest rule.
(In effect, the decision on where to start the match is the first choice
to be made, hence subsequent choices must respect it even if this leads them
to less-preferred alternatives.)