Whats does this mean

Found this piece of code written in ksh. I have no ideas what do the stuff like ${SRF##*\.} do.

SUFFIX=${SRF##*\.}
if [ "$SUFFIX" = "${SRF}" ]; then
SUFFIX=""
fi

I have encountered similar expressions in other programs also. Any pointers on where to learn more about these strange expressions would be really helpful.

Thanks,
JP

from man ksh ...

Some examples:

$ SRF="/path/to/file.ext"
$ echo ${SRF##*.}
ext
$ echo ${SRF%%.*}
/path/to/file
$ echo ${SRF##*/}
file.ext
$ echo ${SRF%/*}
/path/to