extract first 4 letters from a string in matlab

As trolle3000 and b3 mentioned, you use brackets containing indices to extract subsets of the string.

To answer the additional question of how you work on the string, I suggest that you split the string at each space, and convert from hexadecimal to decimal numbers.

s = '01 ED 01 F9 81 C6';
hex2dec(regexp(s, ' ', 'split'))

ans =   
     1
   237
     1
   249
   129
   198