Method to GREEDILY select an optional text using regular expressions?

I'm trying to pick out the name of some folders in a directory, and each have slightly variable names. The names of the folders are:

UD_epoch
UD_Epoch
epoch
Epoch
UD_epoch1
UD_Epoch2

Right now the regular expression I'm using to pick out these folders is:

regexp(nfolders, '(UD.?(e|E)poch\d?)','match')

This picks out the first four folders successfully, but returns the last two as 'UD_epoch' & 'UD_Epoch.' How do I specify that I want the optional element to be included?

Thanks!

Answer 1

[per isakson]

Try

%%
nfolders = {
            'UD_epoch'
            'UD_Epoch'
            'epoch'
            'Epoch'
            'UD_epoch1'
            'UD_Epoch2'
            };
%%
cac = regexp( nfolders, '^(UD_)?(e|E)poch\d?$', 'match' );

it returns

>> cac{:}
ans =
  1×1 cell array
    {'UD_epoch'}
ans =
  1×1 cell array
    {'UD_Epoch'}
ans =
  1×1 cell array
    {'epoch'}
ans =
  1×1 cell array
    {'Epoch'}
ans =
  1×1 cell array
    {'UD_epoch1'}
ans =
  1×1 cell array
    {'UD_Epoch2'}
>> 

/R2018b

[Stephen23]

+1 With the 'once' option makes the outputs easier to work with (no nested cell arrays):

>> regexp( nfolders, '(UD_)?[eE]poch\d*', 'match' ,'once')
ans = 
    'UD_epoch'
    'UD_Epoch'
    'epoch'
    'Epoch'
    'UD_epoch1'
    'UD_Epoch2'

[per isakson]

+1, I'll try to remember that.