How do you plot bar charts in gnuplot?

plot "data.dat" using 2: xtic(1) with histogram

Here data.dat contains data of the form

title 1
title2 3
"long title" 5

You can directly use the style histograms provide by gnuplot. This is an example if you have two file in output:

set style data histograms
 set style fill solid
 set boxwidth 0.5
 plot "file1.dat" using 5 title "Total1" lt rgb "#406090",\
      "file2.dat" using 5 title "Total2" lt rgb "#40FF00"