How to get the pdf of a compiled table only

try this

\documentclass[varwidth]{standalone}[2011/12/21]

One additional step, but might be of interest anyway:

Add \pagestyle{empty} to the preamble, so you have

pdflatex '\documentclass{article}\pagestyle{empty}\begin{document}\input{tab1}\end{document}'

and then run

pdfcrop article.pdf

where article.pdf is the file made by pdflatex. This produces a file article-crop.pdf. pdfcrop is a command line tool included in TeX Live and MikTeX. Without arguments it will crop away the outer whitespace from a PDF.