Extract the coordinates of the gaps between peaks.

[iramai]

Hi everybody, i'm new in SeQanswers.
I have some sequencing data from GEO repository it is written like this:

chr1 1 2001 int
chr1 1001 3001 int
chr1 2001 4001 int
chr1 3001 5001 int
chr1 4001 6001 int


I would like to extract the gap coordinates that are not written, as:

chr1 1 1001
chr1 1001 2001
chr1 2001 3001
chr1 3001 4001


Is it posible in command line?