MATLAB: How to replace a particular string in text file

Question

I have a problem related to efficiency, the code given below will replace the string  and  with '' an ' .' the code is working properly for small size text file ,but the main problem i am facing is that if there are approx 40,0000+ lines in text file then it is taking too much time that no one can't wait so please can anyone suggest me something different which run faster than this, Thanks in advance. 
fid  = fopen('input.txt','r');
f=fread(fid,'*char')';
fclose(fid);
f = regexprep(f,' ','');
f = regexprep(f,' ',' .');
fid  = fopen('output.txt','w');
fprintf(fid,'%s',f);
fclose(fid);

Answer 1

strrep is faster then regexprep

f = strrep(f,' ','');
f = strrep(f,' ',' .');