gnuplot histogram: How to put values on top of bars

using 0 works well with xtic().

plot 'file.dat' using 2:xtic(1) with histogram, '' using 0:2:2 with labels

With this as some sample data file Data.dat:

1 10
2 20
3 15
4 16
5 19
6 5

You could run this script to display boxes and the corresponding value of that box above it:

set key off
plot 'Data.dat' with boxes fill pattern 1, '' u 1:($2 + 0.5):($2) with labels

Notice the u 1:($2 + 0.5):($2) where the 0.5 specifies how much the value is above the box.