How to add text to existing file?

Hi all,

I have a text file data.txt given as:

abc EXECUTE
efg
GHI EXECUTE
EXECUTE
asg
EXECUTE

I want to insert text after EXECUTE (when it appears as the first word).

I want this text output for the same file name.

abc EXECUTE
efg
GHI EXECUTE
EXECUTE
Write something after Execute
asg
EXECUTE
Write something after Execute

I am trying to use MATLAB to precess this. This the code I am trying to write:

%-----------------------------------------------------------
clc
clear all
close all

fid= fopen('data.txt','r+');
line_no=0;
tline=0;
while tline ~= -1 & line_no<6 

      line_no=line_no+1
     tline=fgetl(fid)
    
      if length(findstr('EXECUTE',tline))>0 %& length(tline)<10
          fprintf(fid,'\n Write something after Execute');
          tline=fgetl(fid)
      
      end
  end
  %---------------------------------------------------------------------

However, the text output is little weird. Any help is appreciated.

Sincerely,

Mahendra.

[Mahendra]

abc EXECUTE

efg

GHI EXECUTE

EXECUTE

asg

EXECUTE

[Mahendra]

required output:

abc EXECUTE

efg

GHI EXECUTE

EXECUTE

Write something after Execute

asg

EXECUTE

Write something after Execute

Answer 1

[Walter Roberson]

You need to write the output to a different file, copying the input you want to keep, (and possibly renaming that file to the original name once you are finished the processing.) Writing to a text file "in place" is tricky and is only really possible in fairly limited circumstances.