exporting ascii files with the execute command
 

I need to know how can I export an ascii file from the execute command? (it's a transient simulation) I'm trying with the next line, but I'm getting an error, it say that the command is wrong,

file/export/ascii/File_grid-%t x-velocity y-velocity z-velocity pressure velocity-magnitude dp-dx dp-dy () Can someone tell me the right command? Thanks in advance