Replace multiple lines using regular expression

How do I replace multiple lines using regular Expression?

strTxt = 'Hello! This is just a text and in new line inputParameter'; 
inputParameter = magic(5); 

strTxt = regexprep(strTxt, 'inputParameter', inputParameter); % it is showing error 

[Mathieu NOE]

hello

do it in a for loop (one iteration = one line processed)

Answer 1

[Sameer]

Hi Ravi,

From my understanding, you've encountered an issue when trying to replace a substring in a string using regular expressions. Additionally, you're seeking information on how to replace multiple lines.

The error in your code is occurring because ‘regexprep’ expects the replacement string to be a character array (or string), but ‘inputParameter’ is a matrix since it's generated by the magic(5) function. MATLAB cannot directly convert a numeric matrix into a string format suitable for inclusion in a text string without explicit formatting.

If you want to include a string representation of the ‘inputParameter’ matrix in ‘strTxt’, you need to convert it to a string first. You can use "mat2str" to convert the matrix into a string representation, and then pass that to ‘regexprep’.

www.mathworks.com/help/releases/R2021a/matlab/ref/mat2str.html

Below is the corrected code:

strTxt = 'Hello! This is just a text and in new line inputParameter'; 

inputParameter = magic(5); 

% Convert the matrix to a string representation 
inputParameterStr = mat2str(inputParameter); 

% Replace 'inputParameter' in the text with its string representation 
strTxt = regexprep(strTxt, 'inputParameter', inputParameterStr)

For a multi-line scenario, you can use similar code, as ‘regexprep’ will work regardless of whether the string is single or multi-line. The regular expression 'inputParameter' will match the placeholder text whether it is on the same line or across multiple lines.

Below is an example code:

%Multi-line text
strTxt = sprintf('Hello! This is just a text\nand in new line inputParameter\nwith some more text following it.');
inputParameter = magic(5); 
inputParameterStr = mat2str(inputParameter, 5); 
strTxt = regexprep(strTxt, 'inputParameter', inputParameterStr) 

Hope this helps!

Sameer