Read and Write text file ( .txt )

file = fopen('ficheiro.txt', 'r+');

text = fgets(file);
contains_abc = 0;

while ischar(text)
    disp(text);
    if strfind(text,'abc')
        contains_abc = 1;
    end
    text = fgets(file);
end

if contains_abc == 1
    fprintf(file, '\r\n%s', 'xyz');
end

fclose(file);