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

Asked by Hugo
on 13 Mar 2013
Latest activity Answered by Jos (10584)
on 11 Dec 2013
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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3 Answers

Answer by Jos (10584)
on 11 Dec 2013

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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Answer by Walter Roberson
on 13 Mar 2013

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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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

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Answer by Andreas J. on 11 Dec 2013
Edited by Andreas J. on 11 Dec 2013

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);

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