Description of the problem

Running grdimage with the -x (cores) option fails on GMT 6.4.0 and GMT 6.5.0.dev9+0776994. It seems to think the -x option is being passed in more than once? Noticed at GenericMappingTools/pygmt#2945 (comment)

Full script that generated the error

gmt grdimage @earth_relief_01d_g -RGL -Cgeo -x2 -png map

Full error message

grdimage [ERROR]: Option -x given more than once
grdimage [ERROR]: Option -x parsing failure. Correct syntax:

   [-x[[-]<n>]] .
     Limit the number of cores used in multi-threaded algorithms [Default uses all 16 cores]. If <n> is negative then we select (16 - <n>) cores (or at least 1).
grdimage [ERROR]: Offending option -x2

Actual outcome

grdimage errors

Expected outcome

A map like this should be produced:

System information

• Operating system: Linux
• GMT version (gmt --version): 6.4.0