Help to solve a regexp problem

I'm trying to capture comment block in a string (char array). Regular expression '%.*(\n|$)' captures string from % to the end of the line.

regexp(sprintf('  %%this is a comment'),'%.*(\n|$)','match')

    ans =

      cell

        '% this is a comment'

However, what I want to do is to capture multiple incidence of comment blocks in a char array. The above expression only captures the first one, failing to match '% and this'.

regexp(sprintf('  %%this is a comment\n    %%and this\n'),'%.*(\n|$)','match')

ans =

    cell

      '% this is a comment…'

Could somebody help me about this?

[Stephen23]

To make writing regular expressions easier, you might like to try using my FEX submission that lets you interactively write and develop regular expressions:

https://www.mathworks.com/matlabcentral/fileexchange/48930-interactive-regular-expression-maker

Simply run it to open the interactive figure, then enter your data string, and start playing around with the regular expression. The figure will update and show you the regexp outputs as you change the regular expression. This makes it fast and easy to try different regular expressions, and to check how changes affect the outputs.

PS: This page is very useful too. Lots of information, but worth reading and referring to:

http://www.mathworks.com/help/matlab/matlab_prog/regular-expressions.html

[Kouichi C. Nakamura]

This looks really interesting. I'll surely give it a try. I could help me a lot. Thanks!

Answer 1

[per isakson]

Test this

>> str = sprintf('  %%this is a comment\n    %%and this\n');
>> cac = regexp( str, '[ ]*%[^\n]+', 'match' )
cac = 
    '  % this is a comment'    '    % and this'
>> whos cac
  Name      Size            Bytes  Class    Attributes
  cac       1x2               294  cell

[Kouichi C. Nakamura]

Thanks a lot. Yours included leading spaces (maybe I was not clear enough about what I want to catch), but '%[^\n]+' successfully did the job!

>> cac = regexp(str, '%[^\n]+', 'match' )

cac =

1×2 cell array

    '% this is a comment'    '% and this'

[Guillaume]

Note that your regular expression would have worked if you'd used the non-greedy *?:

regexp(sprintf('  %%this is a comment\n    %%and this\n'),'%.*?(\n|$)','match')

Nonetheless, per's expression is probably more efficient.