Boxwidth

The set boxwidth command is used to set the default width of boxes in the boxes and boxerrorbars styles.

Syntax: 

     set boxwidth {<width>}
     show boxwidth

If a data file is plotted without the width being specified in the third, fourth, or fifth column (or using entry), or if a function is plotted, the width of each box is set by the set boxwidth command. (If a width is given both in the file and by the set boxwidth command, the one in the file is used.) If the width is not specified in one of these ways, the width of each box will be calculated automatically so that it touches the adjacent boxes. In a four-column data set, the fourth column will be interpreted as the box width unless the width is set to -2.0, in which case the width will be calculated automatically. See set style boxerrorbars for more details.

To set the box width to automatic use the command 

     set boxwidth
or, for four-column data, 
     set boxwidth -2

The same effect can be achieved with the using keyword in plot: 

     plot 'file' using 1:2:3:4:(-2)