Plotting a histogram with gmt

Hello everyone, I am using GMT 6.1.0, and I am plotting Histogram, with my code it only gave me the frame without the bar, please what can I do for it to show the bar. below is the code
“gmt pshistogram time.dat -Bxa2f1+l"year of installation” -Bya20f5+l"cummulative number of sites" -BWSne+glightblue -R1994/2015/2/145 -JX5.4i/4.4i -Gred
-L1p -Z1 -W250 >> t.ps" posscbly the data
1994 2
1995 5
1996 6
1997 8
1998 9
1999 11
2000 41
2001 43
2002 44
2003 45
2004 49
2005 51
2006 61
2007 76
2008 99
2009 104
2010 113
2011 117
2012 137
2013 141
2014 142
2015 145
thanks

In this case, due to your data set, you have to plot your data as bars with psxy.

Thank you, it actully work on bars. I think I may have to use bar instead of histogram