I/O string

I'm having a difficulty on replacing the tag with the given replacement word on the given text file for the 3rd subfunction.

here is what I have done so far

function [] = ()
clc;clear
readstring = read_form('form.txt');
[tag,replacement]  = read_sub_tag();
newstring = replace_tags(readstring,tag,replacement);
create_output('Tongue_Twister.txt',newstring)
end
function readstring = read_form(textfile)
readstring = []; %empty readstring
text=fopen(textfile,'r');
if text==-1  %Check if the file opened correctly
    sprintf('File not correctly open')
else
    while ~ feof(text) %to read until the end
        txt=fgets(text); %read every single line
        readstring=sprintf('%s\r',readstring,txt);
        readstring=strcat(readstring);%concatenate the lines into string
    end
end
fclose(text);
return
end
function [tag,replacement]  = read_sub_tag()
tag = []; %empty tag
replacement = []; %empty replacement
sub_tag=fopen('sub.txt','r');
if sub_tag==-1 %check if the file opened correctly
    sprintf('File not correctly opened')
else
    while feof(sub_tag)==0
        sub=fgetl(sub_tag);
        [tag,replacement]=strtok(sub); %to create separate arrays for the tag and replacement
        tag=lower(tag); 
        replacement=strtrim(replacement);
        
    end
    
end
fclose(sub_tag);
return
end
function newstring = replace_tags(readstring,tag,replacement)
newstring = "";
r_s=lower(readstring);
i= strfind(r_s,tag);
tg=i+length(tag);
splitlines(readstring);
for final=readstring(i:tg)
newstring=replace(readstring,final,replacement);
end
return
end
function create_output('Tongue_Twister.txt';newstring)
name=fopen('Tongue_Twister.txt,''wt');
fprintf(name,newstring);
fclose(name);
end

[Walter Roberson]

    while feof(sub_tag)==0
        sub=fgetl(sub_tag);
        [tag,replacement]=strtok(sub); %to create separate arrays for the tag and replacement
        tag=lower(tag); 
        replacement=strtrim(replacement);
        
    end
    

That code is throwing away all of the tags and replacement information, except for the very last one. Even then, in some circumstances you throw away the last one as well, as feof() is not guaranteed to be true when you have just positioned after the last newline in the file; in traditional POSIX file semantics, feof() would not be true in that situation, leading to an empty fget() result.