While the procedure detailed in part 1 is straight forward, it could be easier. I don't like looking for and typing out URLs. Writing loops takes time too. Less experienced people like it even less. Dan Swank wrote a nice wrapper to download data for the North American Regional Reanalysis (NARR). It worked so well that he did get-httpsubset.pl. During May 2006, 95% of the NCDC-NOMADS downloads were done using cURL.

At NCEP, we wanted people to (1) get forecasts using partial-http transfers rather than ftp2u and (2) move off the nomad servers to the more reliable NCO servers. So get_gfs.pl was born. Wanted the script to be easy to use, easy to reconfigure, easier to install and work with Windows.

1. get_gfs.pl.
2. perl
3. cURL

1. The cURL executable needs to be downloaded and put in a directory on your $PATH.
2. The first line of get_gfs.pl should point to the location of the local perl interpreter.
3. Non-windows users can set the $windows flag to "thankfully no" in get_gfs.pl for more efficiency.

      get_gfs.pl data DATE HR0 HR1 DHR VARS LEVS DIRECTORY

Note: some Windows setups will need to type: 

      perl get_gfs.pl data DATE HR0 HR1 DHR DIRECTORY

DATE = start time of the forecast YYYYMMDDHH
       note: HH should be 00 06 12 or 18

HR0 = first forecast hour wanted
HR1 = last forecast hour wanted
DHR = forecast hour increment (forecast every 3, 6, 12, or 24 hours)
VARS = list of variables or "all"
        ex. HGT:TMP:OZONE
        ex. all
LEVS = list of levels, blanks replaced by an underscore, or "all"
        ex. 500_mb:200_mb:sfc
        ex. all
DIRECTORY = directory in which to put the output

example:  perl get_gfs.pl data 2006101800 0 12 6 UGRD:VGRD 200_mb .
example:  perl get_gfs.pl data 2006101800 0 12 12 all sfc .

A user asked if it were possible to mix the variables and levels. For example, TMP @ 500 mb, HGT @ (250 and 700 mb). Of course you could run get-gfs.pl twice but that wouldn't be efficient.

It is possible because get-gfs.pl uses regular expressions and regular expressions are very powerful. All you need to remember is that get-gfs.pl converts the colon and underscore to a vertical bar and space, respectively for the VAR/LEV arguments.

Unix/Linux:

       get-gfs.pl data 2006111500 0 12 12 all 'TMP.500 mb|HGT.(200 mb|700 mb)'  data_dir

Windows:

       get-gfs.pl data 2006111500 0 12 12 all "TMP.500 mb|HGT.(200 mb|700 mb)"  C:\unix\