ans =
'i18n'
regexprep('globalization', match_expr, replace_expr)
ans =
'g11n'
When parsed, a dynamic expression must correspond to a complete, valid regular expression. In
addition, dynamic match expressions that use the backslash escape character (\) require two
backslashes: one for the initial parsing of the expression, and one for the complete match. The
parentheses that enclose dynamic expressions do not create a capturing group.
There are three forms of dynamic expressions that you can use in match expressions, and one form
for replacement expressions, as described in the following sections
Dynamic Match Expressions — (??expr)
The (??expr) operator parses expression expr, and inserts the results back into the match
expression. MATLAB then evaluates the modified match expression.
Here is an example of the type of expression that you can use with this operator:
chr = {'5XXXXX', '8XXXXXXXX', '1X'};
regexp(chr, '^(\d+)(??X{$1})$', 'match', 'once');
The purpose of this particular command is to locate a series of X characters in each of the character
vectors stored in the input cell array. Note however that the number of Xs varies in each character
vector. If the count did not vary, you could use the expression X{n} to indicate that you want to match
n of these characters. But, a constant value of n does not work in this case.
The solution used here is to capture the leading count number (e.g., the 5 in the first character vector
of the cell array) in a token, and then to use that count in a dynamic expression. The dynamic
expression in this example is (??X{$1}), where $1 is the value captured by the token \d+. The
operator {$1} makes a quantifier of that token value. Because the expression is dynamic, the same
pattern works on all three of the input vectors in the cell array. With the first input character vector,
regexp looks for five X characters; with the second, it looks for eight, and with the third, it looks for
just one:
regexp(chr, '^(\d+)(??X{$1})$', 'match', 'once')
ans =
1×3 cell array
{'5XXXXX'}
{'8XXXXXXXX'}
{'1X'}
Commands That Modify the Match Expression — (??@cmd)
MATLAB uses the (??@cmd) operator to include the results of a MATLAB command in the match
expression. This command must return a term that can be used within the match expression.
For example, use the dynamic expression (??@flilplr($1)) to locate a palindrome, “Never Odd or
Even”, that has been embedded into a larger character vector.
Dynamic Regular Expressions
2-73
'i18n'
regexprep('globalization', match_expr, replace_expr)
ans =
'g11n'
When parsed, a dynamic expression must correspond to a complete, valid regular expression. In
addition, dynamic match expressions that use the backslash escape character (\) require two
backslashes: one for the initial parsing of the expression, and one for the complete match. The
parentheses that enclose dynamic expressions do not create a capturing group.
There are three forms of dynamic expressions that you can use in match expressions, and one form
for replacement expressions, as described in the following sections
Dynamic Match Expressions — (??expr)
The (??expr) operator parses expression expr, and inserts the results back into the match
expression. MATLAB then evaluates the modified match expression.
Here is an example of the type of expression that you can use with this operator:
chr = {'5XXXXX', '8XXXXXXXX', '1X'};
regexp(chr, '^(\d+)(??X{$1})$', 'match', 'once');
The purpose of this particular command is to locate a series of X characters in each of the character
vectors stored in the input cell array. Note however that the number of Xs varies in each character
vector. If the count did not vary, you could use the expression X{n} to indicate that you want to match
n of these characters. But, a constant value of n does not work in this case.
The solution used here is to capture the leading count number (e.g., the 5 in the first character vector
of the cell array) in a token, and then to use that count in a dynamic expression. The dynamic
expression in this example is (??X{$1}), where $1 is the value captured by the token \d+. The
operator {$1} makes a quantifier of that token value. Because the expression is dynamic, the same
pattern works on all three of the input vectors in the cell array. With the first input character vector,
regexp looks for five X characters; with the second, it looks for eight, and with the third, it looks for
just one:
regexp(chr, '^(\d+)(??X{$1})$', 'match', 'once')
ans =
1×3 cell array
{'5XXXXX'}
{'8XXXXXXXX'}
{'1X'}
Commands That Modify the Match Expression — (??@cmd)
MATLAB uses the (??@cmd) operator to include the results of a MATLAB command in the match
expression. This command must return a term that can be used within the match expression.
For example, use the dynamic expression (??@flilplr($1)) to locate a palindrome, “Never Odd or
Even”, that has been embedded into a larger character vector.
Dynamic Regular Expressions
2-73