How to extract strings with varied length by regular expression?

As the title, I'm trying to extract substrings from strings. But the substrings have different lengths. For example,

str1 = '2018_a_myid_the_here'; 
str2 = '2018_b_yourid_t_here';

What I want are 'myid' and 'yourid', which are of different length. So I used following code:

expression = '_(\w+)+_';
match = regexp(file_name, expression, 'match');

And I got the result as '_a_myid_the_' and '_b_yourid_t_'. Is there a better way to extract out 'myid' and 'yourid' directly without any further slicing?

Thank you!

Answer 1

[Stephen23]

>> regexp('2018_a_myid_the_here','(?<=^\d+_[a-z]_)[a-z]+','match')
ans = 
    'myid'
>> regexp('2018_b_yourid_t_here','(?<=^\d+_[a-z]_)[a-z]+','match')
ans = 
    'yourid'

For developing and experimenting with regular expressions you might like to download my Interactive Regular Expression tool:

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

[Yujian Wu]

Thank you!