Minecraft fill command using slabs

The problem here is that the command /fill x1 y1 z1 x2 y2 z2 minecraft:stone_slab automatically means /fill x1 y1 z1 x2 y2 z2 minecraft:stone_slab 0, the 0 is added. If you change this 0 to another value, the slab will change it's position; 8 is for the upper stone slabs:

/fill x1 y1 z1 x2 y2 z2 minecraft:stone_slab 8

Note: This technique works only for Minecraft versions 1.12.2 and older. For newer versions, check out the other answer on this question.

In the 1.13 snapshot, use /fill x1 y1 z1 x2 y2 z2 minecraft:oak_slab[type=top].

Yes, the way that you would do this is by using a square bracket at the end of your block type. If you want top slabs, it would be executed as /fill x1 y1 z1 x2 y2 z2 minecraft:stone_slab[type=top]. If you want to find out some more things about /fill, this video will hopefully help:

None of the answers posted here work for me (Minecraft Bedrock 1.16+). I was searching forever to get this to work for me. I finally figured it out, and is kind of tricky. The various "original" stone slabs(stonebrick, andesite, cobble, etc.) are broken down into 4 groups(stone_slab, stone_slab2, etc.). There is an additional data value you need to get more specific(top, double)

This will give you mossy stone brick bottom slabs - /fill x1 y1 z1 x2 y2 z2 stone_slab4 Where as this will give you regular stone top slabs - /fill x1 y1 z1 x2 y2 z2 stone_slab4 10

Use the various information in the slab article wiki to help build your command. Took me a lot of tries to ge the regular stone upper slabs. The "Double Upper" used in the artivle is kind of a bad label as it seems to refer to the single upper slabs instead of 2 slabs together.