MATLAB Programming Fundamentals - MathWorks

Dynamic Expressions

Dynamic expressions allow you to execute a MATLAB command or a regular expression to

determine the text to match.

The parentheses that enclose dynamic expressions do not create a capturing group.

Operator Description Example

(??expr) Parse expr and include the resulting

term in the match expression.

When parsed, expr must correspond

to a complete, valid regular

expression. Dynamic expressions that

use the backslash escape character (\)

require two backslashes: one for the

initial parsing of expr, and one for the

complete match.

'^(\d+)((??\\w{$1}))'

determines how many characters to

match by reading a digit at the

beginning of the match. The dynamic

expression is enclosed in a second set

of parentheses so that the resulting

match is captured in a token. For

instance, matching '5XXXXX'

captures tokens for '5' and

'XXXXX'.

(??@cmd) Execute the MATLAB command

represented by cmd, and include the

output returned by the command in

the match expression.

'(.{2,}).?(??@fliplr($1))'

finds palindromes that are at least

four characters long, such as 'abba'.

(?@cmd) Execute the MATLAB command

represented by cmd, but discard any

output the command returns. (Helpful

for diagnosing regular expressions.)

'\w*?(\w)(?@disp($1))\1\w*'

matches words that include double

letters (such as pp), and displays

intermediate results.

Within dynamic expressions, use the following operators to define replacement terms.

Replacement OperatorDescription

$& or $0 Portion of the input text that is currently a match

$` Portion of the input text that precedes the current match

$' Portion of the input text that follows the current match (use $'' to

represent $')

$N Nth token

$<name> Named token

${cmd} Output returned when MATLAB executes the command, cmd

2 Program Components