DESCRIPTION
Compare GRIB messages contained in two files. If some differences are found it fails returning an error code. Floating-point values are compared exactly by default, different tolerance can be defined see -P -A -R. Default behaviour: absolute error=0, bit-by-bit compare, same order in files.
USAGE
grib_compare [options] grib_file1 grib_file2
OPTIONS
-r
Compare files in which the messages are not in the same order. This option is time expensive.
-b key,key,...
All the keys in this list are skipped in the comparison. Bit-by-bit compare on.
-e
Edition independent compare. It is used to compare GRIB edition 1 and 2.
-2
Enable two-way comparison.
-c key[:i|d|s|n],key[:i|d|s|n],...
Only the listed keys or namespaces (:n) are compared. The optional letter after the colon is used to force the type in the comparison: i->integer, d->float, s->string, n->namespace. See -a option. Incompatible with -H option.
-S start
First field to be processed.
-E end
Last field to be processed.
-a
-c option modifier. The keys listed with the option -c will be added to the list of keys compared without -c.
-H
Compare only message headers (everything except data and bitmap). Bit-by-bit compare on. Incompatible with -c option.
-R key1=relative_error1,key2=relative_error2,...
Compare floating-point values using the relative error as tolerance. key1=relative_error1 will compare key1 using relative_error1. all=relative_error will compare all the floating-point keys using relative_error. Default all=0.
-A absolute error
Compare floating-point values using the absolute error as tolerance. Default is absolute error=0
-P
Compare data values using the packing error as tolerance.
-T factor
Compare data values using factor multiplied by the tolerance specified in options -P -R -A.
-w key[:{s|d|i}]{=|!=}value,key[:{s|d|i}]{=|!=}value,...
Where clause. Messages are processed only if they match all the key/value constraints. A valid constraint is of type key=value or key!=value. For each key a string (key:s), a double (key:d) or an integer (key:i) type can be specified. Default type is string. In the value you can also use the forward-slash character '/' to specify an OR condition (i.e. a logical disjunction) Note: only one -w clause is allowed.
-f
Force. Force the execution not to fail on error.
-V
Version.
-7
Does not fail when the message has wrong length
-v
Verbose.
grib_compare examples
The default behaviour for grib_compare without any option is to perform a bit by bit comparison of the two messages. If the messages are found to be bitwise different then grib_compare switches to a "key based" mode to find out which coded keys are different. To see how grib_compare works we first set the shortName=2d (2 metre dew point temperature) in the file regular_latlon_surface.grib1
> grib_set -s shortName=2d regular_latlon_surface.grib1 2d.grib1