Using textscan makes this task easy, and also allows us to use the '%q' format specifier so that double-quoted strings are kept together (even if they contain delimiter characters).
S = ':WFMPRE:BYT_NR 2;BIT_NR 16;ENCDG ASCII;BN_FMT RI;BYT_OR MSB;WFID "Ch1; DC coupling, 50.00mV/div, 20.00us/div, 10000 points, Sample mode";NR_PT 10000;PT_FMT Y;XUNIT "s";XINCR 20.0000E-9;XZERO -80.8000E-6;PT_OFF 0;YUNIT "V";YMULT 7.8125E-6;YOFF -14.7200E+3;YZERO 0.0E+0;VSCALE 50.0000E-3;HSCALE 20.0000E-6;VPOS -2.3000;VOFFSET 0.0E+0;HDELAY 19.2000E-6;DOMAIN TIME;WFMTYPE ANALOG;CENTERFREQUENCY 0.0E+0;SPAN 0.0E+0;REFLEVEL 0.0E+0';
C = textscan(S,'%q','Delimiter',{';',' '});
C = reshape(C{1},2,[]);
C(1,:) = regexprep(C(1,:),{'^[^A-Z]+','\W'},{'','_'},'ignorecase');
out = struct(C{:})
creates this structure:
out =
WFMPRE_BYT_NR: '2'
BIT_NR: '16'
ENCDG: 'ASCII'
BN_FMT: 'RI'
BYT_OR: 'MSB'
WFID: 'Ch1; DC coupling, 50.00mV/div, 20.00us/div, 10000 points, Sample mode'
NR_PT: '10000'
PT_FMT: 'Y'
XUNIT: 's'
XINCR: '20.0000E-9'
XZERO: '-80.8000E-6'
PT_OFF: '0'
YUNIT: 'V'
YMULT: '7.8125E-6'
YOFF: '-14.7200E+3'
YZERO: '0.0E+0'
VSCALE: '50.0000E-3'
HSCALE: '20.0000E-6'
VPOS: '-2.3000'
VOFFSET: '0.0E+0'
HDELAY: '19.2000E-6'
DOMAIN: 'TIME'
WFMTYPE: 'ANALOG'
CENTERFREQUENCY: '0.0E+0'
SPAN: '0.0E+0'
REFLEVEL: '0.0E+0'
To convert the strings with number values to numeric, then replace the last line with this:
num = cellfun(@str2double,C(2,:));
idx = ~isnan(num)|strcmpi('NaN',C(2,:));
C(2,idx) = num2cell(num(idx));
out = struct(C{:})
which creates this output:
out =
WFMPRE_BYT_NR: 2
BIT_NR: 16
ENCDG: 'ASCII'
BN_FMT: 'RI'
BYT_OR: 'MSB'
... etc
