how to modify a text file replacing an existing string with an user-defined string

Question

Hugo 2013-3-13

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https://ww2.mathworks.cn/matlabcentral/answers/67052-how-to-modify-a-text-file-replacing-an-existing-string-with-an-user-defined-string

评论： Narayanan Krishnamurthi 2022-4-29

Hello,

I want to open an existing text file, modify it adding a string that I define and save the new file. The new string shall replace a string on the existing file, so I must identify it.

Any help appreciated, regards, Hugo

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Answer 1

Jos (10584) 2013-12-11

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https://ww2.mathworks.cn/matlabcentral/answers/67052-how-to-modify-a-text-file-replacing-an-existing-string-with-an-user-defined-string#answer_118064

在 MATLAB Online 中打开

fid = fopen('infile.txt','rt') ;
X = fread(fid) ;
fclose(fid) ;
X = char(X.') ;
% replace string S1 with string S2
Y = strrep(X, S1, S2) ;
fid2 = fopen('outfile.txt','wt') ;
fwrite(fid2,Y) ;
fclose (fid2) ;

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Narayanan Krishnamurthi 2022-4-29

Thank you, very helpful.

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Answer 2

Walter Roberson 2013-3-13

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You cannot do this unless the replacement string is exactly the same length as the original string. Even then it is not recommended. Instead, create an output file, copy everything from the input until you reach the place you want to modify, write the new string without copying the old string, and then copy the rest of the old file to the new one. You can rename the new file to the old name if you need to afterwards.

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Hugo 2013-3-13

How can I do: -create an output file -copy everything from the input until you reach the place you want to modify -write the new string without copying the old string -copy the rest of the old file to the new one. -Rename the new file to the old name if you need to afterwards

Can you please tell me what commands shall I use for each one of this steps?

thanks for replying, Hugo

Vishal Rane 2013-3-15

Refer Low Level File Operations

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Answer 3

Andreas Justin 2013-12-11

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https://ww2.mathworks.cn/matlabcentral/answers/67052-how-to-modify-a-text-file-replacing-an-existing-string-with-an-user-defined-string#answer_118062

编辑：Andreas Justin 2013-12-11

在 MATLAB Online 中打开

Something like this?

%%Preparing
fid = fopen(fullfile('D:\','test.txt'),'w');
fprintf(fid,['function edit(str)',char(13), 'if nargin < 1 || isempty(str)',char(13),...
    'str='''';',char(13),'end',char(13), 'rmpath(matlabroot);',char(13),...
    'edit(str);',char(13), 'addpath(matlabroot);',char(13),'Matlab_extendEditorFunctionality(true);']);
fclose(fid);
clear fid
%%Reading
fid = fopen('D:\test.txt','r');
f = textscan(fid,'%s','Delimiter','\n');
txt = f{:};
%%manipulation
txt = regexprep(txt,'^function','\<FUNCTION\>')
txt = regexprep(txt,'path','\<PATH\>')
txt = regexprep(txt,'(.*)','$1\n');
txt = [txt{:}];
fclose(fid);
%%writing
fid = fopen('D:\test.txt','w');
fprintf(fid,txt)
fclose(fid);