What is wrong in this command about grepping and pandocing?
If you get a blank line from pandoc then something is quite amiss.

My guess is you've got several `pandoc or the tex file is encoded oddly or throwing some error that the version I downloaded from dropbox isn't the same as the one you are using.

$ pandoc test_dummy.tex -f markdown -t html | wc 
     311    1349   11676
$ pandoc test_dummy.tex -f markdown -t html | head

&lt;p&gt;everything - etiology, symptoms, diagnostic tests, grades of aortic valve stenosis&lt;/p&gt;
&lt;p&gt;Aortic regurgitation. The murmur of aortic regurgitation occurs during diastole as the aortic valve fails to lose completely and blood regurgitates from the aorta back into the LV. Murmur - high-pitched decrescendo murmur heard best along left lower sternal border.&lt;/p&gt;
&lt;table&gt;
&lt;caption&gt;Common causes of Aortic Stenosis Among Patients requiring Surgery. % http://emedicine.medscape.com/article/150638-overview#aw2aab6b2b4aa&lt;/caption&gt;
&lt;colgroup&gt;
&lt;col width="38%" /&gt;
&lt;col width="38%" /&gt;
&lt;/colgroup&gt;
&lt;thead&gt;
$ which pandoc
/usr/local/bin/pandoc
$ wc test_dummy.tex 
     210    1049    8801 test_dummy.tex


The troubleshooting would be to check the path to be sure you are using the tools you expect. Then break apart the chain of commands and inspect the beginnings of each output file using things like wc, head or more so you can make sure each link in the chain is working. The post you linked to is an exceptional answer by Kurt in that it explains exactly what the command line tools are doing with grep and why.