set logscale <axes> <base> unset logscale <axes> show logscale
where 4#4axes5#5 may be any combination of x, x2, y, y2, z, and cb in any order, and where 4#4base5#5 is the base of the log scaling. If 4#4base5#5 is not given, then 10 is assumed. If 4#4axes5#5 is not given, then all axes are assumed. unset logscale turns off log scaling for the specified axes.
Examples:
To enable log scaling in both x and z axes:
set logscale xz
To enable scaling log base 2 of the y axis:
set logscale y 2
To enable z and color log axes for a pm3d plot:
set logscale zcb
To disable z axis log scaling:
unset logscale z