wgrib2: -if
Introduction
The -if option returns true or false. If true, then
the next "output" option is executed otherwise it isn't. In order to write
headers into the output file, "inv_output" options are conditionally executed
depending on the flag.
Note, the effects of nesting of -if are not defined
and the flag is reset after processing the record.
The -if option was written so that you can process
the file once and create several output files. For example,
old: wgrib2 -match_inv gribfile >inv
egrep ":(UGRD|VGRD):" inv | wgrib2 -i gribfile -grib winds.grb
grep ":TMP:" inv | wgrib2 -i gribfile -grib tmp.grb
In the above example, the UGRD/VGRD fields are written into winds.grb and
the TMP is written into the tmp.grb file. The above 3 lines can be
rewritten as
new:
wgrib2 gribfile -if ":(UGRD|VGRD):" -grib winds.grb -if ":TMP:" -grib tmp.grb
In the above example, the UGRD/VGRD fields are written into winds.grb and the TMP is written
into the tmp.grb file. Note that you can use any number of
-if options and they use the same output file.
wgrib2 gribfile -if ":(UGRD|VGRD):" -grib save.grb -if ":TMP:" -grib save.grb
The maximum number of -if options on a command
line is limited by (1) system limit of open files
(2) maximum length of a command line,
(3) maximum number of regular expressions allowed MAX_MATCH (wgrib.h),
and (4) maximum number of parsed arguments N_ARGLIST9 (wgrib.h).
Usage
-if X
X is a regular expression
See also: -not,
-end,
-match.
-i.
-not_if.
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