how to replace a specific line in a text file with user data?

Question

taimour sadiq 2023-10-30

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2040551-how-to-replace-a-specific-line-in-a-text-file-with-user-data

评论： taimour sadiq 2023-11-2

采纳的回答： Voss

clear

Messege = 'Hello';

fileID = fopen('SampleFile.txt', 'rt');

textLine = fgetl(fileID);

lineCounter = 1;

while ischar(textLine)

fprintf('%s\n', textLine)

if startsWith(textLine, 'second line')

textLine = Messege % i want to replace this line with messege

disp('Done')

break

end

textLine = fgetl(fileID);

lineCounter = lineCounter + 1;

end

fclose(fileID);

my sample file contains three line data only "first line" "second line" "third line"... i want to replace my hello messge with line starts with string "second line".. code is running fine and display msg 'done' but gives error on messge line

>> Unable to perform assignmentbecause brace indexing is not supported for variable of this type <<

2 个评论
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Les Beckham 2023-10-30

在 MATLAB Online 中打开

SampleFile.txt

When I run your code I see no errors. It is not clear what you are really trying to do. Do you wish to change the contents of the file on disk?

Messege = 'Hello';
fileID = fopen('SampleFile.txt', 'rt');
textLine = fgetl(fileID);
lineCounter = 1;
while ischar(textLine)
    fprintf('%s\n', textLine)
    if startsWith(textLine, 'second line')
        textLine = Messege    % i want to replace this line with messege
        disp('Done')
        break
    end
    textLine = fgetl(fileID);
    lineCounter = lineCounter + 1;
end
first line
second line
textLine = 'Hello'
Done
fclose(fileID);

taimour sadiq 2023-10-30

yes i wish to change the contents of the file on disk... Voss Code Works Fine

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Answer 1

Voss 2023-10-30

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2040551-how-to-replace-a-specific-line-in-a-text-file-with-user-data#answer_1343546

在 MATLAB Online 中打开

SampleFile.txt

input_file = 'SampleFile.txt';
output_file = 'SampleFile_modified.txt';
dbtype(input_file)
1     first line
2     second line
3     third line
Messege = 'Hello';
old_messege = 'second line';
L = readlines(input_file);
L(startsWith(L,old_messege)) = Messege;
writelines(L,output_file);
dbtype(output_file)
1     first line
2     Hello
3     third line

3 个评论
显示 1更早的评论隐藏 1更早的评论

Walter Roberson 2023-11-2

在 MATLAB Online 中打开

SampleFile.txt

input_file = 'SampleFile.txt';
output_file = 'SampleFile_modified.txt';
dbtype(input_file)
1     first line
2     second line
3     third line
Messege = 'Hello';
old_messege = 'second line';
L = string(regexp(fileread(input_file), '\r?\n', 'split'));
L(startsWith(L,old_messege)) = Messege;
[fid, msg] = fopen(output_file, 'w');
if fid < 0
    error('failed to open output file "%s" because "%s"', output_file, msg);
end
fwrite(fid, strjoin(L, newline));
fclose(fid)
ans = 0
dbtype(output_file)
1     first line
2     Hello
3     third line