译者注：如何体现高超的技术，设计一种宏语言吧。
grib_filter 是 ecCodes 高级命令行工具。
该命令逐个处理输入文件中的所有消息，对每个消息应用由用户定义的一组规则。
这些规则由 ecCodes 提供的宏语言定义。注意该宏语言不是完整的编程语言，不能完全替代 ecCodes 提供的 C、Python、Fortran 接口。grib_filter 和 bufr_filter 的宏语言语法相同。
grib_filter 可以实现如下的功能：
if，switch）grib_filter [-o out_file] rules_file in_file1 in_file2 …
输入文件中的每个要素场都被处理，应用 rules_file 中包含的规则。
GRIB 消息仅在执行 write 指令时才写入到输出文件。请将 -o out_file 放到其他参数前。
rules_file 中的说明必须以分号 ; 结尾。
rules_file 中的语法错误会随着行号一同报告。例如对于下面的规则（第二行结尾缺少分号，比较常见的错误）：
$ cat s.filter
print "[centre:s]";
print "[paramId]"
会输出如下的错误消息：
$ grib_filter s.filter levels.grib2
ECCODES ERROR : grib_parser: syntax error at line 2 of (null)
ECCODES ERROR : ecCodes Version: 2.6.0
s.filter: error unable to create action
print "some text"; # this is a comment
print "some text [key]";
向标准输出流中打印信息。
检索中括号中 key 的键值。
如果在消息中没找到某个 key，则该 key 的值会显示为 undef。
可以设置 key 的格式：
[key] -> 原始格式[key:i] -> 整型[key:s] -> 字符串[key:d] -> 双精度浮点型[key!c%^F'S'] -> 数组：c -> columns F -> format(C Style) S -> separatorprint ("filename") "some text [key]";
print "ed = [edition] centre is [centre:s] = [centre:i]";
执行命令
$ grib_filter rule01.filter ../data/simple/levels.grib2
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
ed = 2 centre is babj = 38
# one column 3 decimal digits
print "[distinctLatitudes!1%3.f]";
执行命令
$ grib_filter rule02.filter ../data/simple/levels.grib2
90
90
89
89
89
89
88
88
88
88
87
87
...
# tree columns 5 decimal digits comma separated
print "[latLonValues!3%.5f',']";
执行命令
$ grib_filter rule03.filter ../data/simple/t.t639.grib2 | more
90.00000,0.00000,247.10527,
90.00000,0.28125,247.10527,
90.00000,0.56250,247.10527,
90.00000,0.84375,247.10527,
90.00000,1.12500,247.10527,
90.00000,1.40625,247.10527,
...
write;
将当前消息写入到输出文件中，文件名由命令行的 -o 参数定义。
grib_filter -o outfile rules_file grib_file
如果没有指定 -o 参数，则使用默认值 filter.out。
write "filename_[key]";
将当前消息写入到 filename_[key] 文件中，中括号中的 key 将被从消息中检索出来的值替换。
如果两个消息有不同的 [key] 值，那么它们会写入不同的文件中。
# Creating multiple files
write "[centre]_[typeOfLevel]_[level].grib[edition]";
执行命令
$ grib_filter rule04.filter ../data/simple/levels.grib2
$ ls *.grib*
babj_isobaricInhPa_1000.grib2
babj_isobaricInhPa_950.grib2
babj_isobaricInhPa_975.grib2
append;
将当前消息追加到输出文件中，输出文件由命令行参数 -o 指定。
grib_filter -o outfile rules_file grib_file
如果没有指定 -o 参数，则使用默认值 filter.out。
append "filename_[key]";
将当前消息追加到 filename_[key] 文件中，中括号中的 key 将被从消息中检索出来的值替换。
如果文件不存在，则创建该文件。
如果两个文件的 [key] 值不同，那么它们将被追加到不同的文件中。
append;
执行命令
$ grib_count output.grib2
5
$ grib_filter -o output.grib2 rule05.filter babj_isobaricInhPa_950.grib2
$ grib_count output.grib2
10
set key1 = key2 ; # set key1 to the value of key2
set key = {val1,val2,val3,val4} ;# set an array key
set key = "string" ;# set key to a string
set key = expression ; # set key to an expression
set key = MISSING ; # set value of key to missing
表达式操作符
==：等于!=：不等于is：字符串相等||：或&&：与!：非* / + -：算术运算( )下面的规则将实现 GRIB 2 到 GRIB 1 的转码。
set edition = 1;
write "[file][edition]";
执行命令
$ grib_filter rule06.filter t.t639.grib2
$ grib_ls t.t639.grib21
t.t639.grib21
edition centre typeOfLevel level dataDate stepRange shortName packingType gridType
1 babj isobaricInhPa 1000 20180113 0 t grid_simple regular_ll
1 of 1 messages in t.t639.grib21
1 of 1 total messages in 1 files
set values = {12.2, 14.8, 13.7, 72.3};
print "values = { [values] }";
write "[file].[edition]";
执行命令
$ grib_filter rule07.filter t.t639.grib2
values = { 12.2 14.8 13.7 72.3 }
transient key1 = key2;
定义一个新的 key1，将 key2 的值赋给 key1。
transient key1 = "string";
transient key1 = expression;
表达式操作符与 set 相同：
==：等于!=：不等于is：字符串相等||：或&&：与!：非* / + -：算术运算( )transient mystep = step + 24;
print "step = [step] mystep = [mystep]";
执行命令
$ grib_filter rule08.filter t.t639.grib2
step = 0 mystep = 24
if ( expression ) { instructions }
if ( expression ) { instructions }
else { instructions }
没有 else if，需要创建一个新的 if 代码块。
表达式操作符：
==：等于!=：不等于<：小于，<=：小于或等于>：大于，>=：大于或等于is：字符串相等（!(key is value) 表示 not is）||：或&&：与!：非* / + -：算术运算( )if (shortName is 't') {
write;
}
执行命令
$ grib_ls levels.grib2
levels.grib2
edition centre date dataType gridType stepRange typeOfLevel level shortName packingType
2 babj 20180103 an regular_ll 0 isobaricInhPa 1000 gh grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 975 gh grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 950 gh grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 1000 t grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 975 t grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 950 t grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 1000 u grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 975 u grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 950 u grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 1000 v grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 975 v grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 950 v grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 1000 wz grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 975 wz grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 950 wz grid_jpeg
15 of 15 messages in levels.grib2
15 of 15 total messages in 1 files
$ grib_filter -o out.grib2 rule09.filter levels.grib2
$ grib_ls out.grib2
out.grib2
edition centre date dataType gridType stepRange typeOfLevel level shortName packingType
2 babj 20180103 an regular_ll 0 isobaricInhPa 1000 t grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 975 t grid_jpeg
2 babj 20180103 an regular_ll 0 isobaricInhPa 950 t grid_jpeg
3 of 3 messages in out.grib2
3 of 3 total messages in 1 files
if-else 语句的替代版本。
当需要从多个选项中选择操作时，使用 switch 语句会非常方便。
switch(var) {
case val1:
# set of actions
...
case val2:
# set of actions
...
default:
# default block of actions
}
default：默认情况，在语句为空时也要写出。
print "processing [paramId] [shortName] [stepType]";
switch (shortName) {
case "gh":
print "processing gh";
case "t":
print "processing t";
default:
print "Unexpected parameter";
}
执行命令
$ grib_filter ../../eccodes-grib-tutorial-code/chap_05_grib_filter/rule10.filter levels.grib2
processing 156 gh instant
processing gh
processing 156 gh instant
processing gh
processing 156 gh instant
processing gh
processing 130 t instant
processing t
processing 130 t instant
processing t
processing 130 t instant
processing t
processing 131 u instant
Unexpected parameter
processing 131 u instant
Unexpected parameter
processing 131 u instant
Unexpected parameter
processing 132 v instant
Unexpected parameter
processing 132 v instant
Unexpected parameter
processing 132 v instant
Unexpected parameter
processing 260238 wz instant
Unexpected parameter
processing 260238 wz instant
Unexpected parameter
processing 260238 wz instant
Unexpected parameter
if(centre is "lfpw" &&
(indicatorOfParameter== 6 ||
indicatorOfParameter== 11 ||
indicatorOfParameter== 8) )
{
if(step!=0) {
set typeOfGeneratingProcess=0;
set typeOfProcessedData=0;
} else {
# Other steps
set typeOfProcessedData=1;
switch(typeOfLevel) {
case "hybrid":
set changeDecimalPrecision=1;
case "surface":
set changeDecimalPrecision=2;
case "isobaricInhPa":
if(level > 300) {
print"level > 300";
set level = level*2 + 15;
} # end if (level > 300)
default:
print"Unknown level type!";
}# end switch (typeOfLevel)
}# end if (step!=0)
write;
}# end main if
assert(condition);
如果条件为 false，filter 会出错中止。
示例：
# This filter should be run on GRIB edition 1 only;# abort otherwise
assert (edition == 1) ;
...
执行命令
> grib_filter–o out.grib2 rule.filterx.grib2
ECCODES ERROR : Assertion failure:
binop(access('edition=2'),long(2))