DESCRIPTION

Apply the rules defined in rules_file to each grib message in the grib files provided as arguments.

USAGE

grib_filter [options] rules_file grib_file grib_file ...

OPTIONS


-f

Force. Force the execution not to fail on error.


-o output_grib_file

Output grib is written to output_grib_file. If an output grib file is required and -o is not used, the output grib is written to filtered.out


-M

Multi-field support off. Turn off support for multiple fields in single grib message.


-V

Version.


-g

Copy GTS header.


-G

GRIBEX compatibility mode.


-T T | B | A

Message type. T->GTS, B->BUFR, A->Any (Experimental). The input file is interpreted according to the message type.


-7

Does not fail when the message has wrong length


-v

Verbose.

grib_filter examples

  1. The grib_filter processes sequentially all grib messages contained in the input files and applies the rules to each one of them. Input messages can be written to the output by using the "write" statement. The write statement can be parameterised so that output is sent to multiple files depending on key values used in the output file name. If we write a rules_file containing the only statement: 

    write "../data/split/[centre]_[date]_[dataType]_[levelType].grib[editionNumber]";
    Applying this rules_file to the "../data/tigge_pf_ecmwf.grib2" grib file we obtain several files in the ../data/split directory containing fields split according to their key values 
    > grib_filter rules_file ../data/tigge_pf_ecmwf.grib2
> ls ../data/split
ecmf_20060619_pf_sfc.grib2
ecmf_20060630_pf_sfc.grib2
ecmf_20070122_pf_pl.grib2
ecmf_20070122_pf_pt.grib2
ecmf_20070122_pf_pv.grib2
ecmf_20070122_pf_sfc.grib2


  2. The key values in the file name can also be obtained in a different format by indicating explicitly the type required after a colon.

    The following statement works in a slightly different way from the previous example, including in the output file name the long values for centre and dataType. 
    write "../data/split/[centre:l]_[date]_[dataType:l]_[levelType].grib[editionNumber]";
    Running the same command again we obtain a different list of files. 
    > grib_filter rules_file ../data/tigge_pf_ecmwf.grib2
> ls ../data/split
98_20060619_4_sfc.grib2
98_20060630_4_sfc.grib2
98_20070122_4_pl.grib2
98_20070122_4_pt.grib2
98_20070122_4_pv.grib2
98_20070122_4_sfc.grib2


  3. Other statements are allowed in the grib_filter syntax:

    A complex example of grib_filter rules is the following to change temperature in a grib edition 1 file. 
    # Temperature
if ( level == 850 && indicatorOfParameter == 11 ) {
    print "found indicatorOfParameter=[indicatorOfParameter] level=[level] date=[date]";
    transient oldtype = type ;
    set identificationOfOriginatingGeneratingSubCentre=98;
    set gribTablesVersionNo = 128;
    set indicatorOfParameter = 130;
    set localDefinitionNumber=1;
    set marsClass="od";
    set marsStream="kwbc";
    # Negatively/Positively Perturbed Forecast
    if ( oldtype == 2 || oldtype == 3 ) {
      set marsType="pf";
      set experimentVersionNumber="4001";
    }
    # Control Forecast
    if ( oldtype == 1 ) {
      set marsType="cf";
      set experimentVersionNumber="0001";
    }
    set numberOfForecastsInEnsemble=11;
    write;
    print "indicatorOfParameter=[indicatorOfParameter] level=[level] date=[date]";
    print;
}


  4. The switch statement is an enhanced version of the if statement. Its syntax is the following: 

    switch (key1,key2,...,keyn) {
    case val11,val12,...,val1n:
        # block of rules;
    case val21,val22,...,val2n:
        # block of rules;
    default:
        # [ block of rules ]
}
    Each value of each key given as argument to the switch statement is matched against the values specified in the case statements. If there is a match, then the block or rules corresponding to the matching case statement is executed. Otherwise, the default case is executed. The default case is mandatory, even if empty. The "~" operator can be used to match "anything". Following is an example showing the use of the switch statement: 
    processing paramId=[paramId] [shortName] [stepType]
switch (shortName,indicatorOfParameter) {
    case tp:
        set stepType=accum;
    case ~,2 :
        set typeOfLevel=surface;
    default:
}