MATLAB Programming

3 Basic Program Components
at each iteration. This forced failure is necessary if you want to trace the steps
that MATLAB is taking to resolve the expression.
MATLAB makes a number of passes through the input string, each time
trying another combination of letters to see if a fit better than last match can
be found. On any passes in which no matches are found, the test results in
an empty string. The dynamic script (?@if(~isempty($&))) serves to omit
these strings from the matches cell array:
matches = {};
expr = ['(Euler\s)?(Cauchy\s)?(Boole)?(?@if(~isempty($&)),' ...
'matches{end+1}=$&;end)(?!)'];
regexp('Euler Cauchy Boole', expr);
matches
matches =
'Euler Cauchy Boole' 'Euler Cauchy ' 'Euler '
'Cauchy Boole' 'Cauchy ' 'Boole'
The metacharacters $& (or the equivalent $0), $`, and$' refer to that part
of the input string that is currently a match, all characters that precede the
current match, and all characters to follow the current match, respectively.
These metacharacters are sometimes useful when working with dynamic
expressions, particularly those that employ the (?@cmd) operator.
This example parses the input string looking for the letter g. At each iteration
through the string, regexp compares the current character with g, andnot
finding it, advances to the next character. The example tracks the progress of
scan through the string by marking the current location being parsed with a
^ character.
(The $` and $· metacharacters capture that part of the string that precedes
and follows the current parsing location. You need two single-quotation marks
($'') toexpressthesequence$· when it appears within a string.)
str = 'abcdefghij';
expr = '(?@disp(sprintf(''starting match: [%s^%s]'',$`,$'')))g';
regexp(str, expr, 'once');
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