Use regexp in Matlab to return the value of a variable from a text file

Question

I am reading a text file into Matlab called 'test.txt' which is structured as follows:

$variable1 = answer1; 
$variable2 = answer2;
$variable3 = answer3;

I read the text file into Matlab line by line using the following segment of code:

fid = fopen('test.txt.');
tline = fgetl(fid);
tracks = {};
while ischar(tline)
    tracks{end+1} = regexp(tline, '(?<=^.*\=\s*)(.*)(?=\s*;$)', 'match', 'once');
    tline = fgetl(fid);
end
fclose(fid);

This piece of code returns the value of each variable line by line and would output:

answer1
answer2
answer3

What I want to do is modify my regexp expression so that I can specify the name of the variable to retrieve and have Matlab output the value assigned to the variable specified.

E.g. If I specify in my code to find the value of $variable2, Matlab would return:

answer2

Regards

nrz · Accepted Answer · 2012-04-16 18:26:52Z

2

One possible solution:

function [tracks] = GetAnswer(Filename, VariableName)
fid = fopen(Filename);
tline = fgetl(fid);
tracks = {};

% prefix all $ in VariableName with \ for `regexp` and `regexprep`
VariableName = regexprep(VariableName, '\$', '\\$');

while ischar(tline)
    if (regexp(tline, [ '(', VariableName, ')', '( = )', '(.*)', '(;)' ]))
        tracks{end+1} = regexprep(tline, [ '(', VariableName, ')', '( = )', '(.*)', '(;)' ], '$3');
        % if you want all matches (not only the 1st one),
        % remove the following `break` line.
        break;
    end
    tline = fgetl(fid);
end

fclose(fid);
return

You can call it this way:

Answer = GetAnswer('test.txt', '$variable2')

Answer = 
'answer2'

answered Apr 16, 2012 at 18:26

nrz

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