>It looks like you pass it a file name and it returns the full current path plus the file name. So SYS(2027,'test.txt') will return 'c:\vfp\test.txt' assuming that the current directory is c:\vfp. It doesn't seem that useful because you could just use SET('DEFAULT')+SYS(2003)+'test.txt' and get the same thing. Maybe there's some additional functionality there that I don't see. Also, it works in VFP 6.0, but it's still not documented in the VFP 6.0 help.
>
>In general, I wouldn't use any undocumented functions, especially if there's a pretty easy alternative. You never know if it might disappear in a future version.
>
>>Hi Everybody!
>>
>>I found an undocumented Sys() function in utility.vcx.(filelib class)
>>Does somebody know, what it does?

Then it seems to be an alias to FullPath() function. I've found some undocumented sys() functions back in 2.0 or 2.6, and decided they're probably used internally or are aliases to existing functions. If anyone ever finds a really hidden function which does something useful that can't be achieved otherwise, I'd really be surprised.